A slow-release fertilizer and its preparation method

Abstract

The present invention discloses a slow-release fertilizer, which comprises: (1) fly ash, (2) dipotassium hydrogen phosphate and / or potassium dihydrogen phosphate and / or tripotassium phosphate, and (3) an inorganic base. The slow-release fertilizer is prepared by mixing fly ash, dipotassium hydrogen phosphate and / or potassium dihydrogen phosphate and / or tripotassium phosphate and the inorganic base, calcining at 550-850°C, adding water after cooling, and crystallizing under pressure at a temperature of 110-160°C. The prepared fertilizer P and K nutrient elements are loaded in a porous, high-specific-surface-area microporous molecular sieve, with a high loading amount, slowly released through the environment, and having a long-lasting fertilizer effect. The molecular sieve material has a high specific surface area and cation exchange capacity, and in the presence of Cd 2+ ions, Cr 6+ When used in soil environments with highly toxic heavy metal ions such as ions, it can effectively adsorb heavy metal ions in the environment, control their entry into crops, and protect food health.

Description

Technical Field

[0001] The present invention relates to a slow-release fertilizer and a preparation method thereof. Background Art

[0002] N, P, and K are the main nutrient elements for plant production and also the main components of various fertilizers at present. How to enable crops to efficiently absorb these nutrient elements is a key issue in modern agriculture. A slow-release fertilizer is one that slowly controls the release of the nutrient components in the fertilizer, prolongs the plant's fertilizer absorption time, improves fertilizer utilization rate, reduces release and increases efficiency. The most important feature is that after being applied to the soil, it can inhibit the decomposition rate, slowly release, and then be slowly absorbed by the crops. Because this can make the nutrient components of the fertilizer sufficient to meet the needs of growing crops at different levels, and one application can maintain the role of a long-term support point.

[0003] Fly ash, also known as pulverized fuel ash, is a major industrial solid waste in thermal power plants. It is a gray or gray-black solid powder collected from the tail of the boiler after pulverized coal burns in the boiler. Due to the energy structure, the annual discharge of fly ash in China is very large. The total annual stockpile of fly ash emissions exceeds 1 billion tons, and with the continuous acceleration of the economic construction speed and the continuous increase in power demand, the generation rate of fly ash will continue to increase, accounting for about one-third of the world's total emissions. With the increasing attention of the country and society to environmental issues, how to handle these wastes has always been a concern.

[0004] Fly ash not only contains elements such as Si and Al, but also contains various trace elements such as Zn, Fe, Mn, Cu, and Mo, which are all essential for the growth of crops. Therefore, fly ash has long been used as an agricultural fertilizer. The content of SiO2 in fly ash is about 50-60%, so fly ash silicon fertilizer can be produced. Using fly ash from thermal power plants and potassium salts as raw materials, potassium silicate fertilizer can be produced, which can promote crop growth, improve the drought resistance and lodging resistance of crops, reduce the toxicity of heavy metals in the soil, improve soil air permeability, and avoid soil compaction caused by long-term application of chemical fertilizers. Therefore, using fly ash to prepare chemical fertilizers can not only reduce the problem of fly ash accumulation, but also provide the technological added value of fly ash utilization, and has good development prospects.

[0005] The application of slow and controlled release fertilizers has significantly improved the fertilization effect of fertilizers, effectively ensured the efficient utilization of nutrients, protected the environment in which we live; allowed workers to relax by reducing fertilizer operations; avoided harm to seeds or seedlings due to excessive fertilization; and significantly improved the safety performance of agricultural products. Therefore, slow and controlled release fertilizers are known as high-tech green fertilizers in the 21st century, and they also represent the development direction of the chemical fertilizer industry.

[0006] Chinese Patent CN101265141A discloses a fertilizer synergist, its preparation method and application. The fertilizer synergist consists of 10 - 65 parts by weight of fly ash, 5 - 15 parts by weight of modifier, 20 - 75 parts by weight of carrier and 10 - 65 parts by weight of dispersant. The modifier is selected from sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, calcium oxide, ammonium bicarbonate, plant ash, ethylenediamine, formamide, etc. This product can not only reduce nitrogen loss, promote the absorption and utilization of activated silicon and trace elements by crops, but also improve the physical and chemical properties of acidic soil.

[0007] Chinese Patent CN 107188766 A discloses a method for preparing silicon compound fertilizer from fly ash, which includes the following steps: First, grind fly ash to 150 - 200 mesh, fully react it with dilute hydrochloric acid, and then filter to obtain silicon-containing filter residue. At the same time, evaporate and crystallize the filtrate to obtain a solid mixture containing calcium chloride and magnesium chloride crystals. Then react the silicon-containing filter residue with sodium hydroxide solution to obtain a sodium silicate liquid mixture. Finally, mix the sodium silicate liquid mixture with humic acid, nitrogen fertilizer, phosphate fertilizer, potassium fertilizer, bentonite and trace element fertilizer, etc., and granulate to produce silicon compound fertilizer. The prepared silicon compound fertilizer has a high content of soluble silicon, fully utilizes the elements in fly ash, has more comprehensive nutrients, and has the advantages of increasing crop yield, improving quality and improving soil.

[0008] CN 109232090 A discloses an environment-friendly fly ash-coated slow-release fertilizer and its preparation method. Through the above method, the present invention can slow down the release rate of water-soluble chemical fertilizers in the coating, and prolong the duration of fertilizer efficiency. It is made from the following raw materials: fly ash, sodium hydroxide, EDTA-Ca, EDTA-Na, aluminum sulfate, sodium silicate; modify fly ash to obtain environment-friendly fly ash, then add the product obtained by mixing and heating aluminum sulfate and sodium silicate to the modified fly ash for bonding, and then spray it on the fertilizer to make a chemical fertilizer with slow-release effect. The outstanding feature is that the modified detoxified fly ash used has a large porosity, which can slow down the release rate of water-soluble chemical fertilizers in the coating and prolong the duration of fertilizer efficiency. This patent uses the large porosity of the coating and modified detoxified fly ash to obtain the slow-release effect. The slow-release effect obtained by this method is limited, and the structure of fly ash is not changed.

[0009] In this field, there is an urgent need for fertilizers with excellent slow-release effect, long-lasting fertilizer efficiency and the ability to effectively adsorb heavy metal ions in the environment. Summary of the Invention

[0010] The purpose of the present invention is to solve the problems existing in the prior art and provide a slow-release fertilizer and its preparation method. [[ID=1,6]]

[0011] According to the first embodiment of the present invention, a slow-release fertilizer is provided, which comprises: (1) fly ash, (2) dipotassium hydrogen phosphate (K2HPO4) and / or potassium dihydrogen phosphate (KH2PO4) and / or tripotassium phosphate (K3PO4), (3) an inorganic base, and is prepared by the following steps: mixing the three of (1) fly ash, (2) dipotassium hydrogen phosphate and / or potassium dihydrogen phosphate and / or tripotassium phosphate, and (3) an inorganic base, calcining at 550 - 850 °C, preferably 600 - 800 °C, more preferably 650 - 750 °C (for example, 1 - 5 hours, preferably 1.5 - 3 hours, more preferably about 2 hours), and crystallizing in the presence of water after cooling.

[0012] Further, the crystallization is carried out under the conditions of adding water and pressurizing at a temperature of 110 - 160 °C, preferably 115 - 160 °C, preferably 120 - 155 °C, more preferably 120 - 150 °C, more preferably 120 - 140 °C (for example, 5 - 48 hours, further for example 12 - 36 hours, further for example 24 - 30 hours). The water is preferably deionized water, and the addition amount of water can be 40 - 200 wt% of the mixture of (1) fly ash, (2) dipotassium hydrogen phosphate and / or potassium dihydrogen phosphate and / or tripotassium phosphate, and (3) an inorganic base, for example 50 - 150 wt%, further for example 80 - 100 wt%.

[0013] Further, the mass ratio of (1) fly ash, (2) dipotassium hydrogen phosphate and / or potassium dihydrogen phosphate and / or tripotassium phosphate, and ( 3) an inorganic base is 1:(0.1 - 10.0):(0.1 - 10.0), preferably 1:(0.5 - 5.0):(0.3 - 5.0), preferably 1:(0.8 - 3.0):(0.4 - 3.0), preferably 1:(1.0 - 1.8):(0.5 - 1.5), preferably 1:(1.0 - 1.2):(0.5 - 1). Dipotassium hydrogen phosphate, potassium dihydrogen phosphate, and tripotassium phosphate can be used alone respectively, or two or three of them can be combined. When two or three of them are combined, their mixing ratio can be arbitrary. For example, in the case of using any two of the three, the ratio between the two can be 0.1 - 1:0.1 - 1. In the case of using all three, the mass ratio of dipotassium hydrogen phosphate, potassium dihydrogen phosphate, and tripotassium phosphate can be 0.1 - 1:0.1 - 1:0.1 - 1.

[0014] Further, after crystallization, the product is filtered, washed, and dried. The washing can be carried out by water washing, and the drying can be drying at 30 - 90 °C for 0.5 - 10 hours.

[0015] Further, before mixing, the fly ash is sieved through a 100 - 200 mesh sieve.

[0016] Among them, when the calcination temperature is lower than 550 °C, the amorphous phase and quartz phase of fly ash are still relatively obvious, no new phase is generated, and the slow-release effect is not significantly improved. When the calcination temperature is higher than 850 °C, glass phase appears during alkaline sintering and agglomeration occurs.

[0017] Among them, when the crystallization temperature is lower than 110 °C, no obvious characteristic diffraction peaks of NaX-type molecular sieve appear, and it may not be able to fully exchange harmful heavy metal ions in the soil. When the crystallization temperature is higher than 165 °C, especially at 160 °C, no further effect is obtained, so it is unnecessary. The pressure during crystallization is not particularly limited, as long as the temperature reaches 110 - 160 °C, preferably 120 - 160 °C, more preferably 120 - 145 °C, and more preferably 115 - 120 °C.

[0018] In the present invention, the inorganic base can be selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, ammonia water (for example, with a concentration of 20 - 30 w%, further for example 25 - 28 wt%), etc. In the present application, the base can be used to adjust the pH value and activate the fly ash.

[0019] The fly ash described in the present invention is also called fly ash, which is a main industrial solid waste of thermal power plants. It is a gray or grayish-black solid powder collected from the tail of the boiler after pulverized coal burns in the boiler. Fly ash not only contains elements such as Si and Al, but also contains various trace elements such as Zn, Fe, Mn, Cu, and Mo. The content of SiO2 in fly ash is approximately 50 - 60%.

[0020] According to the second embodiment of the present invention, a method for preparing the above slow-release fertilizer is provided, including the following steps:

[0021] Mix (1) fly ash, (2) dipotassium hydrogen phosphate and / or potassium dihydrogen phosphate and / or tripotassium phosphate, and (3) inorganic base, and calcine at 550 - 850 °C, preferably 600 - 800 °C, more preferably 650 - 750 °C (for example, for 1 - 5 hours, preferably 1.5 - 3 hours, more preferably about 2 h), and crystallize in the presence of water after cooling.

[0022] The crystallization is carried out under the conditions of adding water to the mixture under pressure at a temperature of 110 - 160 °C, preferably 120 - 160 °C, more preferably 120 - 145 °C, and more preferably 115 - 120 °C (for example, for 5 - 48 hours, further for example 12 - 36 hours, further for example 24 - 30 hours). The water is preferably deionized water, and the addition amount of water can be 40 - 200 wt% of the mixture of (1) fly ash, (2) dipotassium hydrogen phosphate and / or potassium dihydrogen phosphate and / or tripotassium phosphate, and (3) inorganic base, for example 50 - 150 wt%, further for example 80 - 100 wt%.

[0023] Further, the mass ratio of (1) fly ash, (2) dipotassium hydrogen phosphate and / or potassium dihydrogen phosphate and / or tripotassium phosphate, and (3) inorganic base is 1:(0.1 - 10.0):(0.1 - 10.0), preferably 1:(0.5 - 5.0):(0.3 - 5.0), more preferably 1:(0.8 - 3.0):(0.4 - 3.0), still more preferably 1:(1.0 - 1.8):(0.5 - 1.5), and most preferably 1:(1.0 - 1.2):(0.5 - 1).

[0024] Further, after crystallization, the product is filtered, washed, and dried. The washing can be carried out with water, and the drying can be carried out at 30 - 90 °C for 0.5 - 10 hours.

[0025] Further, before mixing, the fly ash is sieved through a 100 - 200 mesh sieve.

[0026] In the present invention, the inorganic base can be selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, ammonia water (for example, with a concentration of 20 - 30 w%, further for example 25 - 28 wt%), etc. In this application, the base can be used to adjust the pH value and activate the fly ash.

[0027] In the present invention, the calcination can be carried out in a muffle furnace, crucible, or other suitable calcination equipment. The calcination time can be 1 - 5 hours, preferably 1.5 - 3 hours, and more preferably about 2 hours.

[0028] In the present invention, the crystallization can be carried out for, for example, 5 - 48 hours, further for example 12 - 36 hours, and further for example 24 - 30 hours. There is no particular limitation on the pressure, as long as the temperature reaches 110 - 160 °C, such as 115 - 120 °C, preferably 120 - 160 °C, and more preferably 120 - 145 °C.

[0029] The slow-release fertilizer of the present invention can be used for fertilizing all crops, and can be fertilized according to the conventional methods in the art, with excellent and long-lasting fertilizer efficiency.

[0030] Advantages of the present invention:

[0031] (1) Solve the problems of a large amount of fly ash emissions and accumulation, reduce the harm of fly ash dust, and reduce environmental pollution;

[0032] (2) Improve the comprehensive utilization value of fly ash;

[0033] (3) The prepared fertilizer has P and K nutrient elements loaded in porous and high specific surface area microporous molecular sieves, with a high loading amount. The adsorption and desorption processes conform to thermodynamic and kinetic laws, and are slowly released through the environment, with long-lasting fertilizer efficiency;

[0034] (4) In addition to the additional essential nutrients P and K, fly ash itself also contains a variety of trace elements such as Cu, Fe, Ca, Zn, and Mn, which also make the nutrition of crops more comprehensive and balanced;

[0035] (5) The high specific surface area and cation exchange capacity of molecular sieve materials are unique to Cd 2+ ions, Cr 6+ When used in soil environments with highly toxic heavy metal ions such as ions, it can effectively adsorb heavy metal ions in the environment, control their entry into crops, and protect food health. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a diagram of a slow-release fertilizer leaching device.

[0037] Figure 2 is the XRD spectrum of the pre-product at different calcination temperatures.

[0038] Figure 3 These are the XRD patterns of the products at different hydrothermal crystallization temperatures.

[0039] Figure 4 This is the XRD spectrum of the optimized product.

[0040] Figure 5 is a SEM photograph of the molecular sieve formed after calcination.

[0041] Figure 6 These are the X-ray diffraction patterns of fly ash / potassium dihydrogen phosphate and pure fly ash, where the upper curve is fly ash / potassium dihydrogen phosphate and the lower curve is pure fly ash.

[0042] Figure 7 It is the cumulative release curve of element P released from the sample measured by spectrophotometry.

[0043] Figure 8 is the cumulative release curve of element K in the eluent. DETAILED DESCRIPTION

[0044] The present invention is further described below with reference to the embodiments and accompanying drawings.

[0045] Example 1

[0046] Sieve the original fly ash through a 200-mesh sieve for standby; weigh a certain mass of fly ash, potassium dihydrogen phosphate, and sodium hydroxide using an electronic balance, and mix and grind them evenly in an agate mortar. The mass ratio of fly ash: potassium dihydrogen phosphate: sodium hydroxide is 1:1.1:0.8; put the evenly ground mixture of fly ash, potassium dihydrogen phosphate, and sodium hydroxide into a crucible, and calcine it in a muffle furnace in different batches at 500 °C, 600 °C, 700 °C, and 800 °C for 2 h. After cooling, transfer it to a beaker, then add an appropriate amount of deionized water to the beaker, stir it on a magnetic stirrer at room temperature for 4 h. After standing, transfer the mixed solution to a reaction kettle lined with polyvinyl chloride, and crystallize it at 120 °C for 24 h. Filter, wash, dry, and weigh the crystallized product, and perform XRD characterization on the product.

[0047] Figure 2 The XRD spectra of the pre-products at different calcination temperatures are shown. It can be seen from the figure that the amorphous phase and quartz phase of fly ash are still relatively obvious at 500 °C. At 600 - 800 °C, silicon dioxide reacts with the alkaline substances in it, producing new phases. After reaching 700 °C, the reaction degree increases significantly.

[0048] Example 2

[0049] Sieve the original fly ash through a 200-mesh sieve for standby; weigh a certain mass of fly ash, potassium dihydrogen phosphate, and sodium hydroxide using an electronic balance, and mix and grind them evenly in an agate mortar. The mass ratio of fly ash: potassium dihydrogen phosphate: sodium hydroxide is 1:1.1:0.8; put the evenly ground mixture of fly ash, potassium dihydrogen phosphate, and sodium hydroxide into a crucible, place it in a muffle furnace and calcine it at 750 °C for 2 h. After cooling, transfer it to a container, then add deionized water accounting for 80% of the total mass of fly ash, potassium dihydrogen phosphate, and sodium hydroxide to the container, stir it at room temperature for 4 h. After standing, transfer the mixed solution to a reaction kettle lined with polyvinyl chloride, and crystallize it at 120 °C for 24 h. Filter, wash, dry, and weigh the crystallized product, and perform XRD and SEM characterization on the product. The SEM photo of the slow-release fertilizer formed after calcination is as Figure 5 shown.

[0050] Figure 4 is the X-ray diffraction pattern of the sample after calcination at 750 °C and crystallization at 120 °C. It can be seen from the figure that there is no amorphous diffuse peak, and the quartz phase and mullite phase have also changed, and the diffraction peaks have obvious X-type molecular sieve characteristics.

[0051] Example 3

[0052] Sieve the original fly ash through a 200-mesh sieve for later use; weigh a certain mass of fly ash, potassium dihydrogen phosphate, and sodium hydroxide with an electronic balance, and mix and grind the three evenly with an agate mortar, where the mass ratio of fly ash:potassium dihydrogen phosphate:sodium hydroxide = 1:1.1:0.8; transfer the mixture to a beaker, then add an appropriate amount of deionized water to the beaker, stir on a magnetic stirrer at room temperature for 4 h, after standing, transfer the mixed solution to a reaction kettle lined with polyvinyl chloride, and crystallize at a temperature of 110 - 160 °C for 24 h. Filter, wash, dry, and weigh the products crystallized at each temperature, and perform XRD characterization on the products.

[0053] Figure 3 XRD of the products at different hydrothermal crystallization temperatures is shown. From Figure 3 it can be seen that when the crystallization temperature is above 120 °C, obvious characteristic diffraction peaks of NaX-type molecular sieve will appear near 10°. However, for the samples without high-temperature calcination, although the crystallization temperature is increased to 160 °C, there are still obvious diffuse diffraction peaks of amorphous silica, and the diffraction peaks of quartz phase around 27° also still exist.

[0054] Example 4

[0055] Sieve the original fly ash through a 200-mesh sieve for later use; weigh a certain mass of fly ash, potassium dihydrogen phosphate, and sodium hydroxide with an electronic balance, and mix and grind the three evenly with an agate mortar, where the mass ratio of fly ash:potassium dihydrogen phosphate:sodium hydroxide = 1:0.5:0.5; put the evenly ground mixture of fly ash, potassium dihydrogen phosphate, and sodium hydroxide into a crucible, place it in a muffle furnace and calcine at 700 °C for 2 h. After cooling, transfer it to a beaker, then add an appropriate amount of deionized water to the beaker, stir on a magnetic stirrer at room temperature for 4 h, after standing, transfer the mixed solution to a reaction kettle lined with polyvinyl chloride, and crystallize at a temperature of 120 °C for 24 h. Filter, wash, and dry the crystallized product to obtain a slow-release fertilizer.

[0056] Example 5

[0057] Sieve the original fly ash through a 200-mesh sieve for later use; weigh a certain mass of fly ash, potassium dihydrogen phosphate, and sodium hydroxide with an electronic balance, and mix and grind the three evenly with an agate mortar, where the mass ratio of fly ash:potassium dihydrogen phosphate:sodium hydroxide = 1:3.0:3.0; put the evenly ground mixture of fly ash, potassium dihydrogen phosphate, and sodium hydroxide into a crucible, place it in a muffle furnace and calcine at 700 °C for 2 h. After cooling, transfer it to a beaker, then add an appropriate amount of deionized water to the beaker, stir on a magnetic stirrer at room temperature for 4 h, after standing, transfer the mixed solution to a reaction kettle lined with polyvinyl chloride, and crystallize at a temperature of 120 °C for 24 h. Filter, wash, and dry the crystallized product to obtain a slow-release fertilizer.

[0058] Example 6

[0059] Sieve the as-received fly ash through a 200-mesh sieve for standby use; weigh a certain mass of fly ash, dipotassium hydrogen phosphate, and sodium hydroxide with an electronic balance, and mix and grind the three evenly with an agate mortar, where the mass ratio of fly ash:dipotassium hydrogen phosphate:sodium hydroxide = 1:1.1:0.8; put the evenly ground mixture of fly ash, dipotassium hydrogen phosphate, and sodium hydroxide into a crucible, place it in a muffle furnace in different batches and calcine at 750 °C for 2 h. After cooling, transfer it to a beaker, then add an appropriate amount of deionized water to the beaker, stir on a magnetic stirrer at room temperature for 4 h. After standing, transfer the mixed solution to a reaction kettle lined with polyvinyl chloride and crystallize at 120 °C for 24 h. Filter, wash, dry, and weigh the crystallized product.

[0060] Example 7

[0061] Sieve the as-received fly ash through a 200-mesh sieve for standby use; weigh a certain mass of fly ash, potassium dihydrogen phosphate, and potassium hydroxide with an electronic balance, and mix and grind the three evenly with an agate mortar, where the mass ratio of fly ash:potassium dihydrogen phosphate:potassium hydroxide = 1:1.1:0.5; put the evenly ground mixture of fly ash, potassium dihydrogen phosphate, and potassium hydroxide into a crucible, place it in a muffle furnace and calcine at 750 °C for 2 h. After cooling, transfer it to a beaker, then add an appropriate amount of deionized water to the beaker, stir on a magnetic stirrer at room temperature for 4 h. After standing, transfer the mixed solution to a reaction kettle lined with polyvinyl chloride and crystallize at 120 °C for 24 h. Filter, wash, dry, and weigh the crystallized product.

[0062] Example 8

[0063] Sieve the as-received fly ash through a 200-mesh sieve for standby use; weigh a certain mass of fly ash, potassium dihydrogen phosphate, and 28% ammonia water with an electronic balance, mix and grind fly ash and potassium dihydrogen phosphate evenly with an agate mortar, and add ammonia water to mix, where the mass ratio of fly ash:potassium dihydrogen phosphate:28% ammonia water = 1:1.1:2; put the evenly ground mixture of fly ash, potassium dihydrogen phosphate, and ammonia water into a crucible, place it in a muffle furnace and calcine at 750 °C for 2 h. After cooling, transfer it to a beaker, then add an appropriate amount of deionized water to the beaker, stir on a magnetic stirrer at room temperature for 4 h. After standing, transfer the mixed solution to a reaction kettle lined with polyvinyl chloride and crystallize at 120 °C for 24 h. Filter, wash, dry, and weigh the crystallized product.

[0064] Comparative Example 1

[0065] Sieve the original fly ash through a 200-mesh sieve for later use; weigh a certain mass of fly ash and potassium dihydrogen phosphate with an electronic balance, and mix and grind them evenly in an agate mortar, where the mass ratio of fly ash:potassium dihydrogen phosphate = 1:1; after grinding, put the evenly ground mixture into a sealed autoclave, add appropriate amount of water, stir and disperse, control the reaction temperature at about 150 °C, and after cooling, measure its phase structure (X-ray diffraction pattern) and compare it with the pure fly ash phase. The results are as Figure 6 shown. No new phases are formed, and the XRD diffraction peaks of the obtained product do not have the characteristics of molecular sieves.

[0066] Comparative Example 2

[0067] Sieve the original fly ash through a 200-mesh sieve for later use; weigh a certain mass of fly ash, calcium phosphate, potassium chloride and sodium hydroxide with an electronic balance, and mix and grind the three of them evenly in an agate mortar, where the mass ratio of fly ash:calcium phosphate:potassium chloride:sodium hydroxide = 1:0.8:0.8:0.8; put the evenly ground mixture of fly ash, calcium phosphate, potassium chloride and sodium hydroxide into a crucible, place it in a muffle furnace and calcine at 700 °C for 2 h, transfer it to a beaker after cooling, then add appropriate amount of deionized water to the beaker, stir on a magnetic stirrer at room temperature for 4 h, after standing, transfer the mixed solution to a reaction kettle lined with polyvinyl chloride together, and crystallize at 120 °C for 24 h. Filter, wash and dry the crystallized product to obtain a slow-release fertilizer. No new phases are formed, and the XRD diffraction peaks of the obtained product do not have the characteristics of molecular sieves.

[0068] Study on the release of nutrient elements K and P in Application Example 1

[0069] The slow-release performance of the compound fertilizer in Example 2 was detected by the static leaching method in a soil column. Lay filter paper, slow-release fertilizer, fine sand and gravel in the separating funnel from bottom to top in sequence, as Figure 1 shown, add a certain amount of deionized water, and open the funnel valve to continuously collect the leaching solution for 30 days. The filter paper prevents the loss of the slow-release fertilizer at the bottom layer from interfering with the detection. The fine sand is used to simulate the presence of soil, and the gravel is used to prevent the turbulence when adding deionized water from washing away the fine sand and slow-release fertilizer.

[0070] The content of K element in the leaching solution was determined by flame atomic absorption spectrometry, and a graph was plotted with the release time corresponding to the cumulative release concentration. The content of P element in the leaching solution was determined by ammonium molybdate colorimetry, with the reagent blank as the reference. The absorbance of the sample solutions at 4 d, 7 d, 12 d, 15 d, 18 d, 23 d, and 29 d was measured three times repeatedly.

[0071] Figure 7It is the cumulative release curve of P element released from the sample measured by spectrophotometry. It can be seen from the figure that the release curve of P is relatively fast in the first 10 days, with about 7.8% released. The content of P leached out during the subsequent 20 days decreased significantly. By the end, the content of P lost by leaching was about 8.4%. The main P element remained in the soil and fertilizer.

[0072] Figure 8 It is the cumulative release curve of K element in the leaching solution. It can be seen from the figure that the cumulative release concentration of K gradually increases with the increase of time, and the overall release rate remains unchanged. Within 28 days, the concentration of K gradually increases from 4% to 25%, and the remaining about 75% of K remains in the soil system.

[0073] The slow-release fertilizers of Comparative Example 1 and Comparative Example 2 were used for the same experiment as described above. The results showed that the loss of P and K by leaching reached more than 50%, indicating that their slow-release effect was poor.

[0074] Application Example 2

[0075] The slow-release fertilizer of Example 2 was applied to a test field in Huainan. Wheat was planted in winter, and corn was planted after wheat was harvested. It was only necessary to apply 50 kg per mu once, and then supplement the application of conventional amount of nitrogen fertilizer urea. The growth of the crops was good, and the yield per mu increased by more than 15% compared with the application of similar amounts of commercially available nitrogen, phosphorus and potassium fertilizers.

[0076] Application Example 3

[0077] The slow-release fertilizer of Example 2 was applied to a test field in Huainan. Wheat was planted in winter, and corn was planted after wheat was harvested. It was only necessary to apply 50 kg per mu once, and then supplement the application of conventional amount of nitrogen fertilizer urea. In the comparative test field (adjacent to the test field with basically the same soil conditions), commercially available inorganic nitrogen, phosphorus and potassium fertilizers with equal fertilizer efficiency were used. No cadmium content was detected in the crops applying the slow-release fertilizer of the present application, while the cadmium content in the comparative test field was 0.15 mg / kg (determined by the cadmium detection method specified in the "National Food Safety Standard Determination of Cadmium in Foods" (GB 5009.15-2014)).

[0078] The above shows and describes the basic principles, main features and advantages of the present invention. The above embodiments and the description in the specification only illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements will all fall within the scope of the present invention claimed. The scope claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A slow-release fertilizer comprising: (1) fly ash, (2) dipotassium hydrogen phosphate and / or potassium dihydrogen phosphate and / or tripotassium phosphate, and (3) an inorganic base, which is prepared by the following steps: (1) fly ash, (2) dipotassium hydrogen phosphate and / or potassium dihydrogen phosphate and / or tripotassium phosphate, and (3) an inorganic base are mixed, calcined at 600-800°C, and crystallized in the presence of water after cooling; the crystallization comprises adding water and crystallizing under pressure at a temperature of 120-160°C, wherein the mass ratio of (1) fly ash, (2) dipotassium hydrogen phosphate and / or potassium dihydrogen phosphate and / or tripotassium phosphate, and (3) the inorganic base is 1:(0.1-10.0):(0.1-10.0), Wherein, the inorganic base is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, and ammonia water.

2. The slow-release fertilizer according to claim 1, wherein Calcination at 650-750℃.

3. The slow-release fertilizer according to claim 1, wherein The mass ratio of (1) fly ash, (2) dipotassium hydrogen phosphate and / or potassium dihydrogen phosphate and / or tripotassium phosphate, and (3) inorganic alkali is 1: (0.5-5.0): (0.3-5.0).

4. The slow-release fertilizer according to claim 1, wherein The mass ratio of (1) fly ash, (2) dipotassium hydrogen phosphate and / or potassium dihydrogen phosphate and / or tripotassium phosphate, and (3) inorganic alkali is 1: (0.8-3.0): (0.4-3.0).

5. The slow-release fertilizer according to claim 4, wherein The mass ratio of (1) fly ash, (2) dipotassium hydrogen phosphate and / or potassium dihydrogen phosphate and / or tripotassium phosphate, and (3) inorganic alkali is 1: (1.0-1.8): (0.5-1.5).

6. The slow-release fertilizer according to claim 5, wherein The mass ratio of (1) fly ash, (2) dipotassium hydrogen phosphate and / or potassium dihydrogen phosphate and / or tripotassium phosphate, and (3) inorganic alkali is 1: (1.0-1.2): (0.5-1).

7. The slow-release fertilizer according to any one of claims 1 to 3, wherein The crystallization comprises adding water under pressure and crystallizing at a temperature of 120-155° C.; and / or After crystallization, the product was filtered, washed and dried.

8. The slow-release fertilizer according to claim 7, wherein The crystallization comprises adding water and performing crystallization under pressure at a temperature of 120-140°C.

9. The slow-release fertilizer according to claim 1, wherein Before mixing, the fly ash was sieved through a 100-200 mesh screen.

10. A method for preparing a slow-release fertilizer, comprising the following steps: (1) fly ash, (2) dipotassium hydrogen phosphate and / or potassium dihydrogen phosphate and / or tripotassium phosphate, and (3) an inorganic base are mixed, calcined at 600-800°C, cooled, and crystallized in the presence of water; the crystallization comprises adding water and crystallizing under pressure at a temperature of 120-160°C, wherein the mass ratio of (1) fly ash, (2) dipotassium hydrogen phosphate and / or potassium dihydrogen phosphate and / or tripotassium phosphate, and (3) the inorganic base is 1:(0.1-10.0):(0.1-10.0), and the inorganic base is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, and ammonia water.

11. The preparation method according to claim 10, wherein Calcination at 650-750℃.

12. The preparation method according to claim 10, wherein The mass ratio of (1) fly ash, (2) dipotassium hydrogen phosphate and / or potassium dihydrogen phosphate and / or tripotassium phosphate, and (3) inorganic alkali is 1: (0.5-5.0): (0.3-5.0).

13. The preparation method according to claim 12, wherein The mass ratio of (1) fly ash, (2) dipotassium hydrogen phosphate and / or potassium dihydrogen phosphate and / or tripotassium phosphate, and (3) inorganic alkali is 1: (0.8-3.0): (0.4-3.0).

14. The preparation method according to claim 13, wherein The mass ratio of (1) fly ash, (2) dipotassium hydrogen phosphate and / or potassium dihydrogen phosphate and / or tripotassium phosphate, and (3) inorganic alkali is 1: (1.0-1.8): (0.5-1.5).

15. The preparation method according to claim 14, wherein The mass ratio of (1) fly ash, (2) dipotassium hydrogen phosphate and / or potassium dihydrogen phosphate and / or tripotassium phosphate, and (3) inorganic alkali is 1: (1.0-1.2): (0.5-1).

16. The preparation method according to any one of claims 10 to 15, wherein The crystallization comprises adding water under pressure and crystallizing at a temperature of 120-155° C.; and / or After crystallization, the product was filtered, washed and dried.

17. The preparation method according to claim 16, wherein The crystallization comprises adding water and performing crystallization under pressure at a temperature of 120-140°C.

18. The preparation method according to claim 10, wherein Before mixing, the fly ash was sieved through a 100-200 mesh screen.

Images