Method for preparing molecular sieve slow release fertilizer from coal gangue and product thereof

Abstract

The invention discloses a method for preparing a molecular sieve slow release fertilizer from coal gangue and a product thereof. The method comprises the following steps: firstly, calcining coal gangue, and then adopting an alkali fusion-hydrothermal synthesis method and a crystallization reconstruction process. The coal gangue roasting activation temperature is controlled, the crystallization temperature, time and other parameters are adjusted, and the synthesis conditions of the molecular sieve are optimized. In order to deeply analyze the structure and morphology of the obtained sample, the sample is characterized by using analysis technical means such as XRD (X-Ray Diffraction) and SEM (Scanning Electron Microscope). After an ideal molecular sieve sample is obtained, the composite molecular sieve slow-release phosphate fertilizer is finally prepared, and the slow-release rule of the nutrient element phosphorus in the slow-release fertilizer sample is tested through a soil column leaching method at room temperature. Nutrient substances in the fertilizer are dispersed into pore structures of the molecular sieves, and slow release of nutrient elements can be controlled in the use process, so that slow release and synergism can be achieved, the land quality can be improved, and damage to the environment is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of fertilizer and solid waste resource utilization, and in particular to a technical method for preparing slow-release fertilizer by utilizing coal-based solid waste coal gangue. Background Art

[0002] The commonly used slow-release fertilizer is prepared by wrapping a layer of coating material on the outside of traditional fertilizers. It can improve fertilizer utilization, increase crop yields, and reduce environmental pollution. It is widely used in the fields of crop, fruit and vegetable, and horticultural fertilization. Slow-release fertilizer can slowly release fertilizer according to the growth cycle of crops. One application can meet the nutrient needs of crops throughout the growth period. While improving crop quality, it nourishes the soil and preserves fertilizers, effectively solving the problems of environmental pollution and low utilization rate of chemical fertilizers.

[0003] The reason for low fertilizer utilization rate is that nitrogen, phosphorus and other elements in fertilizer exist in the form of corresponding ions. Some components are easily soluble in water and easily dissolved during rainfall or irrigation, resulting in loss and difficulty in retention. Crops have different biological characteristics for the required amount of nutrients at different growth stages, resulting in an imbalance between nutrient supply and crop demand, wasting resources, and chemical components lost in fertilizers will cause environmental pollution, affect soil fertility, reduce crop yields, pollute groundwater systems, and cause eutrophication of lakes. The use of slow-release fertilizers can effectively solve the current problem of insufficient fertilizer utilization.

[0004] my country is rich in coal resources and the mining volume is also considerable. However, as a by-product of coal mining and coal washing, the amount of coal gangue is also increasing year by year. According to statistics, the amount of coal gangue produced in 2023 reached 825 million tons, a year-on-year increase of 2.1%. Despite this, the utilization rate of coal gangue is also gradually increasing, reaching 73.6%, a year-on-year increase of 0.4 percentage points. This means that about 607 million tons of coal gangue have been effectively utilized. However, there are still a lot of coal gangue that has not been used. They are piled up like mountains, which puts a certain amount of pressure on the environment. Using coal gangue to make organic fertilizer can not only reduce waste emissions, but also make full use of resources and convert them into fertilizers that are beneficial to plant growth. Domestic and foreign scholars have studied the production of fertilizers from coal gangue, and the main research content is to select one or more of inorganic minerals, chemical fertilizers, microorganisms, manure, straw and sludge to mix with coal gangue to make fertilizers. However, there are still many problems with coal gangue fertilizer. For example, the degree of solidification of organic matter in coal gangue is relatively high, the decomposition and conversion rate is not high enough, and the effectiveness of carbon source needs to be improved. In addition to increasing crop yields, the effects of coal gangue fertilizer in improving soil and controlling the release of nutrients need to be improved. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention uses coal gangue as raw material to prepare molecular sieve carriers to construct slow-release fertilizers, disperses the nutrients in the fertilizer into the pore structure of the molecular sieve, and can control the slow release of nutrients during use, thereby achieving slow-release efficiency, improving land quality, and reducing damage to the environment.

[0006] The technical solution adopted by the present invention is: The present invention prepares a gangue-based molecular sieve carrier after structural reconstruction of the gangue, loads phosphate fertilizer, and conducts research on the controlled release of phosphorus nutrient elements; the present invention prepares a new fertilizer with the advantages of slow release and synergy, synergistic effect of mineral elements, and prevention of soil compaction.

[0007] A method for preparing molecular sieve slow-release fertilizer using coal gangue comprises the following steps: 1) After crushing and grinding the original coal gangue, sieve it with a 100-mesh screen and activate the coal gangue at high temperature; 2) After activation, the coal gangue and sodium hydroxide are mixed and ground evenly, then transferred to a crucible and placed in a muffle furnace for roasting at 500-600℃ for 2-3h; 3) Take out the powder, add deionized water, stir for 12-24 hours, let it stand for 12-24 hours, pour out the upper alkaline clear liquid after stratification, transfer the remaining precipitate to a polyvinyl chloride lined reactor, add deionized water to 60-70% of the reactor volume, place the reactor in an oven at 100-110° C. for crystallization for 12-728 hours, after cooling, pour out the alkaline solution in the reactor, retain the precipitate, wash by centrifugation until the pH of the supernatant reaches 7, and obtain the molecular sieve carrier after drying; 4) Take a certain mass of molecular sieve product and the same mass of fertilizer, transfer them to a mixer and mix them with the molecular sieve and grind them finely to obtain molecular sieve slow-release fertilizer.

[0008] Step 1) The activation temperature is 800-900°C and the activation time is 2-3h.

[0009] In step 2), the mass ratio of activated coal gangue to sodium hydroxide is 0.9-1.2:1. More preferably, the mass ratio of coal gangue to sodium hydroxide is 1.0:1.0. The molecular sieve crystal particles are uniform in size and well dispersed, and the regular octahedral structure can be clearly observed.

[0010] In step 3), the crystallization temperature is preferably 100° C., and the crystallization time is 24-48 hours, more preferably, the crystallization time is 48 hours.

[0011] Step 4) The fertilizer is a type of substance that improves soil properties and soil fertility, mainly including ammonium phosphate fertilizers, water-soluble fertilizers of large amounts of elements, fertilizers of medium amounts of elements, biological fertilizers, organic fertilizers, multi-dimensional field energy concentrated organic fertilizers, etc. Preferably, it is a combination of one or more of nitrogen fertilizer, phosphate fertilizer, potash fertilizer, and organic fertilizer. More preferably, it is a combination of phosphate fertilizer and other fertilizers, and the phosphate fertilizer is preferably potassium dihydrogen phosphate.

[0012] Step 4) The mass ratio of molecular sieve to fertilizer is 1~10:1~10.

[0013] The molecular sieve slow-release fertilizer can be added with a granulation auxiliary agent and a tableting auxiliary agent to obtain a slow-release fertilizer tablet.

[0014] The granulation auxiliary agent is starch, and the tableting auxiliary agent is magnesium stearate, and the addition amount is 1-10wt.%.

[0015] Further preferably, the added amount of starch and magnesium stearate in the slow-release fertilizer is 5wt.%.

[0016] The molecular sieve slow-release fertilizer prepared by the preparation method.

[0017] The molecular sieve slow-release fertilizer is used in improving saline-alkali soil.

[0018] The present invention prepares a gangue-based molecular sieve slow-release fertilizer, which is promising as a saline-alkali soil improver and is used for improving sea saline-alkali soil and conducting demonstrations to increase the organic matter content of saline-alkali soil. The experiment determines the leaching and dissolution rate of P in the saline-alkali soil, and can calculate the retention rate of the saline-alkali soil for the fertilizer effect of phosphate fertilizer. The experiment was followed up and monitored for one month to achieve the goal of "treating waste with waste and turning waste into treasure."

[0019] A gangue-based molecular sieve slow-release phosphate fertilizer, the preparation steps of which are as follows: Step 1: preparing molecular sieve carrier material by alkali melting hydrothermal reconstruction; Step 2: After mixing with the phosphate fertilizer, add granulation auxiliary starch and tableting auxiliary magnesium stearate to obtain slow-release fertilizer tablets.

[0020] The addition amount of starch and magnesium stearate in the slow-release fertilizer is 5wt.%.

[0021] The present invention uses pretreated coal gangue and sodium hydroxide to synthesize a molecular sieve with a specific pore size and morphology by regulating the hydrothermal synthesis conditions. Compared with the existing method of calcining and activating with sodium carbonate and then adjusting the pH value with NaOH solution, the method is simple and the types of reagents used are reduced. A slow-release phosphate fertilizer based on coal gangue molecular sieve is constructed, which is expected to improve the soil quality of poor-quality environments such as saline-alkali soil and improve land quality.

[0022] In order to gain a deeper understanding of the crystal structure and surface morphology of the prepared samples, the present invention uses characterization methods such as XRD and SEM for analysis. Through this series of experiments, the optimal conditions for preparing molecular sieves are determined. The molecular sieves prepared according to the optimal conditions obtained by characterization are then mixed and ground with potassium dihydrogen phosphate to prepare molecular sieve slow-release fertilizers, which are characterized by XRD and SEM. After leaching the sample soil column, the phosphorus content is accurately determined using an ultraviolet spectrophotometer to further explore the release law of the P element in the slow-release fertilizer. This study not only provides a new way for the efficient utilization of coal gangue, but also provides strong support for the preparation and application of slow-release fertilizers.

[0023] The coal gangue selected in the present invention has a Si / Al molar ratio of about 2.2.

[0024] In an alkaline environment, Si and Al elements in coal gangue mostly exist in the form of silicates and aluminates dissolved in the solution. After the raw materials are mixed, silicates and aluminates undergo polymerization to form an initial aluminate gel. Secondly, under the influence of specific temperature, alkalinity, and pressure, depolymerization and structural rearrangement occur, thereby generating primary structural units composed of zeolite crystals. Finally, the primary structural units are rearranged around the hydrated cations to form a polyhedral structure, followed by polymerization and connection between the polyhedrons, and finally forming zeolite molecular sieve crystals.

[0025] The chemical formula for preparing molecular sieves using sodium hydroxide as an alkali source is: Al2O3·2SiO2·2H2O+6NaOH→2Na2SiO3+2NaAlO2+5H2O The gangue is crushed as it is, put into a grinder for grinding, sieved with a 100-mesh screen, and activated at a high temperature of 800-900°C to obtain the raw materials required for molecular sieve synthesis. An electronic balance was used to weigh a certain mass of activated coal gangue and sodium hydroxide, with a mass ratio of 0.9-1.2. All the raw materials were transferred to an agate mortar, mixed and ground evenly, and then transferred to a crucible, placed in a muffle furnace at 550-600°C for calcination for 2-3 hours, the powder was taken out and transferred to a beaker, deionized water was added, and the open part of the beaker was covered with plastic wrap to prevent foreign matter from falling into the suspension. The beaker was placed on a magnetic stirrer for stirring for 24 hours and then allowed to stand for 24 hours. The upper alkaline clear liquid after stratification was poured out, and the remaining precipitate was transferred to a polyvinyl chloride lined reactor, deionized water was added to 60-70% of the volume of the reactor, and the reactor was placed in an oven at 100°C for crystallization for 48 hours. The reactor was placed in a fume hood and naturally cooled, and the alkali solution in the reactor was poured out to retain the precipitate, and the supernatant was washed by centrifugation until the pH value reached 7, and the molecular sieve carrier was obtained after drying for standby use.

[0026] Weigh a certain mass of molecular sieve product and the same mass of potassium dihydrogen phosphate, transfer to a mixer and mix with the molecular sieve and grind finely to obtain a molecular sieve slow-release fertilizer. Add 5% starch and continue to mix evenly, and add an appropriate amount of ethanol to keep the mixture evenly, place in a 60℃ oven to dry for 1 hour, take out and granulate, make tablets, and obtain tablet products.

[0027] XRD data show that the position of the high-intensity characteristic peak of slow-release phosphate fertilizer is different from the position and intensity of the characteristic peaks of molecular sieve and potassium dihydrogen phosphate. It is speculated that after the molecular sieve and potassium dihydrogen phosphate are mixed and ground, the molecular sieve exerts its adsorption function and adsorbs the phosphorus element in potassium dihydrogen phosphate. The phosphorus particles are filled in the pores of the molecular sieve, which changes the overall crystal form. The possible reason is that the phosphate group also interacts with the cations in the molecular sieve.

[0028] The slow-release phosphate fertilizer prepared by the present invention has a cumulative release rate of phosphorus element showing a gradually increasing trend and has a good slow-release effect.

[0029] Beneficial effects:

[0030] The present invention uses industrial waste coal gangue as raw material, restructures it, obtains a molecular sieve carrier with a high specific surface area, and utilizes its high adsorption to prepare compound fertilizer.

[0031] By dispersing the nutrients in the fertilizer into the pore structure of the molecular sieve, the slow release of nutrients can be controlled during use, thereby achieving slow-release efficiency, improving land quality, and reducing damage to the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a product photo of the molecular sieve slow-release fertilizer tablet prepared by the present invention; Figure 2 It is a one-month cumulative release curve of the nutrient element P of the molecular sieve slow-release fertilizer prepared by the present invention; Figure 3 Whether the molecular sieve is prepared by calcination XRD pattern; Figure 4 Ash-alkali ratio 1.0:1.0 (a), 1.0:0.6 (b) and 1.0:2.0 (c); Figure 5 SEM of crystallized molecular sieve at 100℃(a) and 120℃(b); Figure 6 SEM images of crystallization time 24h (a), 48h (b), 36h (c), and 72h (d); Figure 7 XRD patterns of slow-release fertilizer, molecular sieve and potassium dihydrogen phosphate; Figure 8 . P dissolution rate of molecular sieve phosphate fertilizer and ordinary phosphate fertilizer. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments of the present invention are provided for the purpose of illustration and description, and are not intended to be exhaustive or to limit the present invention to the disclosed forms. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments are selected and described in order to better illustrate the principles and practical applications of the present invention, and to enable those of ordinary skill in the art to understand the present invention and thereby design various embodiments with various modifications suitable for specific uses.

[0034] The following examples use coal gangue from the Xuzhou mining area, whose Si / Al molar ratio is about 2.2.

[0035] Example 1 Different ash-alkali ratios The gangue was crushed as it was, put into a grinder for grinding, sieved with a 100-mesh screen, and activated at 800°C for 2 hours to obtain the raw materials required for molecular sieve synthesis.

[0036] An electronic balance was used to weigh a certain mass of activated coal gangue and sodium hydroxide, with mass ratios of 1.0:0.6, 1.0:1.0, and 1.0:2.0, respectively. All raw materials were transferred to an agate mortar, mixed and ground evenly, and then transferred to a crucible, placed in a muffle furnace and roasted at 550°C for 2h. The powder was taken out and transferred to a beaker, deionized water was added, and a plastic wrap was covered on the open part of the beaker to prevent foreign matter from falling into the suspension. The beaker was placed on a magnetic stirrer for stirring for 24h and then allowed to stand for 24h. The upper alkaline clear liquid after stratification was poured out, and the remaining precipitate was transferred to a polyvinyl chloride-lined reactor, deionized water was added to 60-70% of the volume of the reactor, and the reactor was placed in an oven at 100°C for crystallization for 48h. The reactor was placed in a fume hood and naturally cooled, and the alkali solution in the reactor was poured out to retain the precipitate, which was washed by centrifugation until the pH of the supernatant reached 7, and the molecular sieve carrier was obtained after drying for standby use.

[0037] Figure 3 It is the XRD spectra of powder and coal gangue calcined and uncalcined at 550°C before the hydrothermal synthesis step. The molecular sieve prepared by the calcination operation has a high-intensity diffraction peak at 2Theta of 6.53°, which is detected as having the characteristic diffraction peak of NaX type molecular sieve. The molecular sieve prepared without calcination has a diffraction peak at 2Theta of 6.53°, which proves that a very small amount of NaX type molecular sieve appears. It has a high-intensity diffraction peak at 2Theta of 27.50° and is much higher than the diffraction peak intensity of the molecular sieve prepared by the calcination step. The peak position is similar to the original coal gangue, and it is speculated that part of the original sample did not participate in the reaction. It shows that when the NaX molecular sieve is formed, the crystal form and crystallinity of the synthesized molecular sieve after the calcination operation are better.

[0038] Figure 4 These are SEM photos of the products of coal gangue powder and sodium hydroxide (ash-alkali ratio) of different masses at a crystallization temperature of 100°C and a crystallization time of 48h. It can be seen from the figure that the molecular sieve particles with an ash-alkali ratio of 1.0:0.6 are uneven in size and have an unstable crystal form; the molecular sieve crystal particles with an ash-alkali ratio of 1.0:1.0 are uniform in size and have better dispersion. The regular octahedral structure can be clearly observed, and the SEM structure and XRD results can confirm each other; although the molecular sieve crystal structure with an ash-alkali ratio of 1.0:2.0 is also a regular octahedron, there are clumping morphological structures. By comparing the XRD scanning images, it is speculated to be unactivated quartz.

[0039] Example 2 Effect of different crystallization temperatures on products The gangue is crushed as it is, put into a grinder for grinding, sieved with a 100-mesh screen, and activated at 800°C to obtain the raw materials required for molecular sieve synthesis.

[0040] An electronic balance was used to weigh a certain mass of activated coal gangue and sodium hydroxide, with a mass ratio of 1.0:1.0. All raw materials were transferred to an agate mortar, mixed and ground evenly, and then transferred to a crucible, placed in a muffle furnace and calcined at 550°C for 2h, the powder was taken out and transferred to a beaker, deionized water was added, and plastic wrap was covered on the open part of the beaker to prevent foreign matter from falling into the suspension. The beaker was placed on a magnetic stirrer for stirring for 24h and then allowed to stand for aging for 24h. The upper alkaline clear liquid after stratification was poured out, and the remaining precipitate was transferred to a polyvinyl chloride-lined reactor, deionized water was added to 60-70% of the volume of the reactor, and the reactor was placed in an oven for crystallization at 100°C and 120°C for 48h, respectively. The reactor was placed in a fume hood and naturally cooled, and the alkali solution in the reactor was poured out to retain the precipitate, which was washed by centrifugation until the pH of the supernatant reached 7, and the molecular sieve carrier was obtained after drying for standby use.

[0041] Figure 5 The SEM photos of the products with different crystallization temperatures when the ash-alkali ratio is 1:1 and the crystallization time is 48h. When the crystallization temperature is 100℃, the SEM photos clearly show that the particle size is uniform and the dispersion is good. The SEM photos show that different morphological structures coexist with the octahedron. When the crystallization temperature is 120℃, the SEM photos show that different morphological structures occupy the vast majority of the proportion, and the octahedron structure is greatly reduced. According to the spectrum, it is speculated that the substance may be a NaSOD type molecular sieve. Therefore, when the synthesis crystallization temperature is 100℃, the crystal form of the NaX type molecular sieve is the best.

[0042] Example 3 Effect of different crystallization times on the product The gangue is crushed as it is, put into a grinder for grinding, sieved with a 100-mesh screen, and activated at 900°C to obtain the raw materials required for molecular sieve synthesis.

[0043] An electronic balance was used to weigh a certain mass of activated coal gangue and sodium hydroxide, with a mass ratio of 1.0:1.0. All raw materials were transferred to an agate mortar, mixed and ground evenly, and then transferred to a crucible, placed in a muffle furnace and calcined at 550°C for 2h, the powder was taken out and transferred to a beaker, deionized water was added, and plastic wrap was covered on the open part of the beaker to prevent foreign matter from falling into the suspension. The beaker was placed on a magnetic stirrer for stirring for 24h and then allowed to stand for aging for 24h. The upper alkaline clear liquid after stratification was poured out, and the remaining precipitate was transferred to a polyvinyl chloride lined reactor, deionized water was added to 60-70% of the volume of the reactor, and the reactor was placed in an oven for crystallization at 100°C for 24, 48, 36 and 72h, respectively. After the reactor was placed in a fume hood and cooled naturally, the alkali solution in the reactor was poured out, the precipitate was retained, and the supernatant was washed by centrifugation until the pH value reached 7. The molecular sieve carrier was obtained after drying and used for standby.

[0044] Figure 6 The SEM photos of the products with different crystallization times when the ash-alkali ratio is 1:1 and the crystallization temperature is 100℃. When the crystallization time is 24h, the SEM photos show irregular and poorly dispersed amorphous structures; when the crystallization time is 48h, the SEM photos show that the octahedral molecular sieve with uniform particle size and good dispersion can be clearly observed; when the crystallization time is 36h and 72h, the SEM photos show that some octahedral crystals and other morphological crystals appear. Therefore, when the synthesis crystallization time is 48h, the crystal form of NaX type molecular sieve is the best.

[0045] Example 4 Weigh a certain mass of molecular sieve product and the same mass of potassium dihydrogen phosphate, transfer to a mixer and mix with the molecular sieve and grind finely to obtain a molecular sieve slow-release fertilizer. Add 5% starch and continue to mix evenly, and add an appropriate amount of ethanol to keep the mixture evenly mixed. Place in a 60°C oven to dry for 1 hour, take out and granulate, make tablets, and obtain tablet products. The product is as follows Figure 1 shown.

[0046] Take a sand core funnel, spread filter paper at the bottom of the hole, evenly spread a layer of saline-alkali soil on the filter paper, weigh the prepared molecular sieve slow-release fertilizer sample and transfer it to the upper layer of saline-alkali soil, and then evenly spread sand and gravel on it, so that the liquid can flow down slowly and evenly during the elution of the soil column, and fully contact with the molecular sieve slow-release fertilizer to ensure effective extraction. Take a 100mL beaker and place it under the sand core funnel as a container for the elution liquid. At the same time, the elution and dissolution experiment of ordinary phosphate fertilizer (potassium dihydrogen phosphate) was compared. The comparison effect of the two is as follows: Figure 8 shown.

[0047] Prepare phosphorus standard solution and determine the P release pattern. Accurately weigh 12g, 15g, 18g, 21g, and 24g (±0.001g) of potassium dihydrogen phosphate solid particles, add a small amount of deionized water, stir and mix evenly, dissolve the solid particles completely and transfer to a 50mL volumetric flask to prepare a series of gradient concentrations of 0.24mg / L, 0.31mg / L, 0.36mg / L, 0.42mg / L, and 0.48mg / L phosphoric acid solutions.

[0048] The series of gradient solutions were transferred to 25 mL colorimetric tubes, 3 mL of ammonium molybdate mixed solution and 3 mL of ascorbic acid solution were added and mixed evenly, and color was developed at room temperature for 30 min. After the UV spectrophotometer was preheated, deionized water and an equal amount of antimony molybdenum anti-color developer were used as reference solutions, the absorbance of each concentration at 729 nm was measured, and the phosphorus concentration standard curve was drawn using Excel.

[0049] pass Figure 7 It can be seen that the XRD data of potassium dihydrogen phosphate show that a high-emphasis diffraction peak appears at 2Theta of 24.44°, which is a characteristic diffraction peak of potassium dihydrogen phosphate crystals; the XRD data of slow-release fertilizer show that a high-emphasis diffraction peak appears at 2Theta of 34.31°, and diffraction peaks appear at 6.41°, 27.02°, and 31.07°, and there is no high-intensity diffraction peak at 24.44°. The position of the high-intensity characteristic peak of the slow-release fertilizer is different from the position and intensity of the characteristic peaks of the molecular sieve and potassium dihydrogen phosphate. It is speculated that after the molecular sieve and potassium dihydrogen phosphate are mixed and ground, the molecular sieve exerts its adsorption function and adsorbs the phosphorus element in the potassium dihydrogen phosphate. The phosphorus particles are filled in the pores of the molecular sieve to change the overall crystal form. The possible reason is that the phosphate group and the remaining Na+ ions in the molecular sieve form crystalline salts. These phosphorus-containing substances can be adsorbed on the surface or pores of the molecular sieve to form a molecular sieve composite phosphate fertilizer, which can be released into the environment at a relatively slow rate during use, thereby enhancing the fertilizer efficiency cycle of the phosphate fertilizer and achieving the purpose of reducing application and increasing efficiency.

[0050] The XRD spectrum of the slow-release fertilizer is quite different from that of the molecular sieve and potassium dihydrogen phosphate. Compared with the XRD data of the molecular sieve prepared under the best conditions, the intensity of the diffraction peak at 6.41° of the slow-release fertilizer 2Theta is much lower than that of the molecular sieve at 6.41°, indicating that a small amount of molecular sieve crystal structure exists in the slow-release fertilizer. It is speculated that some molecular sieves have not reacted with potassium dihydrogen phosphate and remain in the slow-release fertilizer product. Figure 8 It can be seen that compared with the P dissolution curve of fertilizer without coal gangue as molecular sieve carrier, its release rate is obviously higher than that of phosphate fertilizer with molecular sieve carrier, and it is easily dissolved in water, reaching about 50% in about a week and 70% in 10 days.

[0051] according to Figure 2It can be seen that the cumulative release rate of phosphorus shows a gradually increasing trend. The linear fitting of the cumulative release rate of phosphorus in the first week of leaching and the release time gives a trend line y = 0.0985x - 0.0107, R² = 0.9918, and the linear fitting of the cumulative release rate of phosphorus and the release time after one week of leaching gives a trend line y = 0.0187x + 0.3055, R² = 0.9797. The release rate of P element from the prepared slow-release fertilizer is generally increasing; observing the chart and comparing the slopes of the two trend lines, the slope of the fitting curve in the first week after leaching is significantly greater than the slope of the fitting curve after one week of leaching, which can indicate that the growth rate of the slow-release fertilizer is larger in the first week after leaching, and the growth rate decreases after the first week, and the P element accumulates at a lower rate.

[0052] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field and related fields without creative work should fall within the scope of protection of the present invention. The structures, devices and operating methods not specifically described and explained in the present invention are implemented according to the conventional means in the field unless otherwise specified and limited.

Claims

1. A method for preparing molecular sieve slow-release fertilizer from coal gangue, characterized in that: The steps include: 1) After crushing and grinding the gangue as it is, sieving it and activating it at high temperature; 2) After activation, the coal gangue and sodium hydroxide are mixed and ground evenly, then transferred to a crucible and placed in a muffle furnace for roasting at 500-600℃ for 2-3h; 3) Take out the powder, add deionized water, stir for 12-24 hours, and then stand for aging for 12-24 hours. Pour out the upper alkaline clear liquid after stratification, add deionized water to the remaining precipitate, crystallize at 100-110°C for 12-72 hours, cool, pour out the alkaline solution, retain the precipitate, wash the precipitate by centrifugation until the pH of the supernatant reaches 7, and dry to obtain the molecular sieve carrier; 4) Take a certain mass of molecular sieve products and fertilizers, transfer them to a mixer and mix them with the molecular sieves to grind them finely to obtain molecular sieve slow-release fertilizers.

2. The method for preparing molecular sieve slow-release fertilizer from coal gangue according to claim 1, characterized in that: Step 1) The activation temperature is 800-900°C and the activation time is 2-3h.

3. The method for preparing molecular sieve slow-release fertilizer from coal gangue according to claim 1, characterized in that: In step 2), the mass ratio of activated coal gangue to sodium hydroxide is 0.9-1.2:

1.

4. The method for preparing molecular sieve slow-release fertilizer from coal gangue according to claim 1, characterized in that: In step 3), the crystallization temperature is 100° C. and the crystallization time is 48 hours.

5. The method for preparing molecular sieve slow-release fertilizer from coal gangue according to claim 1, characterized in that: Step 4) The fertilizer is one or a combination of nitrogen fertilizer, phosphorus fertilizer, potassium fertilizer and organic fertilizer.

6. The method for preparing molecular sieve slow-release fertilizer from coal gangue according to claim 1, characterized in that: Step 4) The mass ratio of molecular sieve to fertilizer is 1~10:1~10.

7. The method for preparing molecular sieve slow-release fertilizer from coal gangue according to claim 1, characterized in that: The molecular sieve slow-release fertilizer can be added with a granulation auxiliary agent and a tableting auxiliary agent to obtain a slow-release fertilizer tablet.

8. The method for preparing molecular sieve slow-release fertilizer from coal gangue according to claim 7, characterized in that: The amount of granulation auxiliary agent added in the slow-release fertilizer is 1-10wt.%, and the amount of tableting auxiliary agent added is 1-10wt.%.

9. The molecular sieve slow-release fertilizer prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the molecular sieve slow-release fertilizer according to claim 9 in improving saline-alkali soil.

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