Potassium ferrate bottom-oriented enriched slow-release agent as well as preparation method and application thereof

Abstract

The invention discloses a potassium ferrate bottom-oriented enrichment slow-release agent and a preparation method and application thereof, and belongs to the technical field of bottom-oriented enrichment slow-release agents, and the preparation method comprises the following steps: S1, adding polyethylene glycol into water glass, dissolving, adding lithium hydroxide, acidifying, aging, washing, drying, grinding and calcining to obtain a modified carrier; s2, adding a potassium hydroxide solid into the hypochlorous acid solution, adding ferric hydroxide, continuously adding the potassium hydroxide solid, stirring at constant temperature, reacting to obtain a black purple solution, cooling, filtering and drying to obtain a potassium ferrate crude product; s3, adding the potassium ferrate crude product in the S2 into a 3M potassium hydroxide solution for dissolving, adding the modified carrier in the S1, stirring under an ultrasonic condition, then adding a potassium hydroxide solid to be saturated, keeping the temperature, standing, carrying out suction filtration, cleaning a filter cake, and drying to obtain a composite material; s4, grinding and sieving the composite material obtained in S3, mixing with a bottom enrichment agent, and tabletting to obtain a potassium ferrate bottom enrichment slow-release agent; the pond substrate can be improved.

Description

Technical Field

[0001] This invention relates to the field of bottom-accumulating slow-release agents, and more specifically, to an aquaculture bottom sediment improver, namely a potassium ferrate bottom-accumulating slow-release agent, its preparation method, and its application. Background Technology

[0002] With the increasing demand for aquaculture and the continuous rise in stocking density, uneaten feed, feces, dead animal and plant carcasses, as well as chemicals such as pesticides, disinfectants, and antibiotics accumulate at the bottom of ponds, forming black sludge. If the sludge is not effectively treated, the concentration of organic matter in the sludge will increase, the number of anaerobic microorganisms will rise, nitrogen and phosphorus content will increase, and pH and biochemical oxygen demand will exceed normal ranges, resulting in decreased water transparency and a greenish water color. This not only severely damages the micro-ecological environment of the bottom sediment but also leads to the accumulation of toxic and harmful substances, causing the bottom sediment environment to deteriorate and ultimately endangering the health of farmed fish.

[0003] In ponds with abundant silt, the oxidative decomposition of organic matter consumes oxygen from the bottom layer, leading to an anaerobic environment. Under these anaerobic conditions, anaerobic bacteria proliferate, decomposing organic matter and producing large amounts of toxic byproducts such as NH3 and NO. 2- Anaerobic bacteria produce organic and inorganic acids from the decomposition of organic matter, such as H2S, CH4, organic acids, lower amines, and thiols. These substances are significantly toxic to farmed fish and accumulate in the water. Mild effects include impaired fish growth, while severe effects can lead to poisoning, death, or even pond collapse, resulting in substantial economic losses. Furthermore, the organic and inorganic acids produced by anaerobic bacteria decomposing organic matter acidify the substrate, significantly lowering the pH level and further affecting fish respiration, leading to a series of abnormal changes such as decreased metabolism and stunted growth.

[0004] Currently, commonly used methods for improving pond bottom sediment include physical, chemical, and biological methods. Among them, chemical methods are more widely used, with commonly used agents including potassium persulfate compound salt, potassium ferrate, calcium peroxide, and quicklime. However, chemical methods have three major drawbacks in practical applications: 1. The agents dissolve too quickly, making it difficult to achieve long-term effects; 2. After the effective components diffuse, the concentration in the bottom sediment is insufficient; 3. The agents have limited functional effects and are difficult to completely remove harmful substances from the bottom sediment.

[0005] Therefore, it is necessary to provide a new amendment that can be used to improve the bottom sediment of ponds. Summary of the Invention

[0006] In view of the problems existing in the prior art, the purpose of this invention is to provide a potassium ferrate bottom-accumulation slow-release agent, its preparation method and application. The potassium ferrate bottom-accumulation slow-release agent prepared by this method can improve the bottom sediment of ponds in a long-term and concentrated manner, thereby repairing or maintaining the stability of the pond bottom sediment environment, and thus providing a suitable living environment for farmed fish in the pond.

[0007] To solve the above problems, the present invention adopts the following technical solution.

[0008] A method for preparing a potassium ferrate bottom-enriched sustained-release agent, the preparation steps are as follows: S1: Polyethylene glycol is added to water glass solution, heated and stirred until dissolved, then lithium hydroxide is added and stirred until dissolved, acidified, and then aged at room temperature. After aging, a modified gel is obtained, which is washed, slowly heated and dried, then ground and calcined to obtain a modified carrier. S2: A certain mass of potassium hydroxide is added to sodium hypochlorite for the first dissolution, and ferric hydroxide semi-solid is added for the second dissolution. Then potassium hydroxide is added again, and the mixture is stirred at a constant temperature for the third dissolution. After cooling, filtration and drying, crude potassium ferrate is obtained. S3: Add the crude potassium ferrate obtained in step S2 to a 3M potassium hydroxide solution and stir until dissolved. Then add the modified carrier obtained in step S1 and stir twice under ultrasonic conditions. Then add potassium hydroxide solid until saturated. After keeping warm and standing, filter. Wash the filter cake with anhydrous ethanol and dry to obtain potassium ferrate composite material. S4: Grind and sieve the potassium ferrate composite material obtained in step S3 and mix it with the bottom enrichment agent. After mixing, compress the mixture into tablets to obtain the potassium ferrate bottom enrichment sustained-release agent.

[0009] Furthermore, in step S1, the concentration of the acetic acid aqueous solution is 1M-2M.

[0010] Furthermore, in step S2, the potassium hydroxide is industrial grade with a content ≥90%; the polyethylene glycol has a molecular weight of 4000-6000, preferably 6000.

[0011] Furthermore, in step S1, the modulus of the water glass is 3.0-3.2, and the mass concentration is 5-8%; the amount of lithium hydroxide added is 0.2-0.5% of the mass of sodium silicate solute in the water glass solution, and the amount of polyethylene glycol added is 1-3% of the mass of sodium silicate solute in the water glass; in step S2, the mass of potassium hydroxide added initially is 30-40% of the total mass of potassium hydroxide.

[0012] Furthermore, in step S2, the available chlorine content of the sodium hypochlorite is approximately 15-20%.

[0013] Furthermore, in step S3, the ultrasonic intensity is 0.5-2 W / cm². 2 The ultrasound time is 20-40 minutes.

[0014] Furthermore, in step S3, the mass ratio of crude potassium ferrate to 3M potassium hydroxide solution is 1:15-20; the mass ratio of crude potassium ferrate to modified carrier is 1:3-4.

[0015] Furthermore, in step S4, the bottom-oriented enriching agent is magnesium silicate fine powder with a particle size of 5-8 μm; the amount of bottom-oriented enriching agent added is 0.7-1% of the mass of the potassium ferrate composite material.

[0016] Furthermore, in step S2, the method for preparing the ferric hydroxide semi-solid is as follows: ferric chloride solution is placed in a flask, and then liquid alkali is slowly added to react. After the reaction is completed, the mixture is filtered, and the filter cake is the ferric hydroxide semi-solid. The molar ratio of ferric chloride to total potassium hydroxide is 1:6-8; the molar ratio of ferric chloride to sodium hypochlorite is 1:1.5-1.8.

[0017] Furthermore, the ferric chloride is industrial grade with a content of ≥98%.

[0018] Furthermore, the ferric chloride solution has a mass fraction of 20-30%; the liquid alkali is sodium hydroxide with a mass concentration of 30%, and the molar ratio of ferric chloride to sodium hydroxide in the liquid alkali is 1:3-3.5.

[0019] Furthermore, the liquid alkali should be added slowly under stirring conditions, at least meeting the following requirements: stirring speed 300-400 rpm, liquid alkali addition rate 5-7 mL / min.

[0020] Furthermore, in step S1, the specific operation of slow heating and drying is as follows: the washed modified gel is slowly heated to 105°C in air at a rate of 5-8°C / min to obtain a dry gel.

[0021] Furthermore, in step S1, the acidification pH is 4.5, the acidification temperature is 75-80℃, and the acidification time is 1-1.5h; the aging time is 12-16h; the calcination temperature is 200-400℃, and the calcination time is 1-2h; in step S2, the first dissolution temperature is 0-30℃, the third dissolution temperature is 40-60℃, and the dissolution time is 20-40min; the cooling temperature is -5-0℃; the drying conditions are under vacuum at 60℃ for 1-3h; and all operations in step S3 are carried out at 0-5℃.

[0022] Furthermore, in step S4, the specific steps of the tableting operation are as follows: first, pre-compression is performed at a pressure of 0.3-0.5 MPa, and then the pressure is gradually increased to 0.5-1 MPa, with a total tableting time of 15-30 seconds.

[0023] Furthermore, in step S1, the dissolution temperature for both dissolutions is 75-80℃, the stirring speed is 600-800rpm, and the dissolution time is 20-30min.

[0024] Furthermore, the acidification operation described in step S1 is specifically as follows: slowly add an aqueous acetic acid solution until the pH reaches 4.5, and then continue stirring at a constant temperature for 1-1.5 hours.

[0025] Furthermore, the acetic acid aqueous solution was added at a rate of 3-4 mL / min.

[0026] Furthermore, the washing operation described in step S1 specifically involves rinsing with pure water until the pH reaches 7, and then rinsing with anhydrous ethanol 2-3 times.

[0027] Furthermore, in step S1, the specific surface area of ​​the modified carrier BET is 500-520 m² / g.

[0028] Furthermore, in step S2, the first dissolution is carried out under temperature-controlled stirring at a stirring speed of 200-300 rpm; the second dissolution is carried out under rapid stirring at a stirring speed of 400-500 rpm; and the third dissolution is carried out under temperature-controlled rapid stirring at a stirring speed of 400-500 rpm.

[0029] Furthermore, in step S2, the filtration method is: using a No. 2 glass frit funnel for vacuum filtration.

[0030] Furthermore, all operations in step S3 are carried out under low-temperature stirring conditions, and at least the following conditions must be met: temperature 0-5℃, stirring speed 600-800rpm.

[0031] Furthermore, in step S4, the sieve used for screening is 32 mesh. Studies have found that, under this preferred condition, controlling the average particle size ensures better uniformity of the components within the compressed sustained-release tablet and more suitable tablet strength.

[0032] Furthermore, in step S4, the mixing is carried out under stirring conditions, with a stirring speed of 600-800 rpm and a stirring time of 10-20 min.

[0033] The present invention also provides a potassium ferrate bottom-enrichment sustained-release agent, which is prepared by the above-described method for preparing a potassium ferrate bottom-enrichment sustained-release agent.

[0034] This invention also provides the application of the above-mentioned potassium ferrate bottom-accumulation slow-release agent in improving the bottom sediment of ponds.

[0035] Compared with the prior art, the advantages of this invention are: I. This scheme uses readily available and inexpensive water glass as the silicon source to prepare the carrier. The sodium ion content is reduced by increasing the modulus of the water glass. Lithium hydroxide is added to react with the water glass to form a protective film on its surface, which isolates water corrosion and reduces the proportion of sodium ions. After modification, the water glass product has significantly improved moisture resistance and stability. In addition, this scheme effectively avoids the collapse of pores caused by the volume shrinkage of the gel during the heat treatment process by controlling the acidification rate and pH and using a slow gradient heating drying and then calcining stabilization treatment method. This effectively preserves the pore structure in the carrier, resulting in a three-dimensional dendritic aggregate structure, forming a stable network with a large specific surface area and strong adsorption. The assembly of the modified water glass carrier and potassium ferrate can effectively limit the direct contact between potassium ferrate and water molecules, allowing only water molecules to slowly permeate and release potassium ferrate slowly.

[0036] II. The bottom-enriching slow-release agent used in this scheme is a fine powder produced during the flash drying process in the production of magnesium silicate. This fine powder usually has no commercial value and is often disposed of in landfills. Research by this invention has found that it has a significant bottom-enrichment effect on the concentration distribution of potassium ferrate after dissolution, greatly increasing the concentration of potassium ferrate at the bottom and achieving a targeted effect. At the same time, the presence of magnesium silicate not only does not affect the stability of potassium ferrate or pollute the water quality, but also plays a synergistic role due to its own adsorption properties, thus turning waste into treasure.

[0037] Third, this invention employs a two-step method to directly synthesize potassium ferrate, avoiding the catalytic decomposition of potassium ferrate by ferric ions. Simultaneously, it directly uses potassium hydroxide, replacing the traditional process of first generating sodium ferrate with sodium hydroxide, then filtering, and finally replacing the sodium ferrate with potassium hydroxide to prepare potassium ferrate. This simplifies the operation and significantly reduces the loss of effective components caused by filtration and decomposition. Furthermore, the use of a high-concentration sodium hypochlorite solution increases the reactant concentration, accelerates the reaction rate, and promotes the forward reaction, thereby increasing the yield of potassium ferrate. Attached Figure Description

[0038] Figure 1 The figure shows the test results of the bottom enrichment effect in test example 2. Detailed Implementation

[0039] Example 1:

[0040] (1) Preparation of modified carrier: 100g of a 5% water glass solution (modulus 3.2) was added to a round-bottom flask. 0.05g of polyethylene glycol 6000 was added while stirring at 800rpm. The mixture was preheated to 75℃ and stirred at 800rpm for 20min. Then, 0.025g of lithium hydroxide was added, and the mixture was stirred at 800rpm for 25min at a constant temperature. Next, 1M acetic acid aqueous solution was added dropwise at a rate of 3mL / min until the pH reached 4.5. The addition of acetic acid aqueous solution was stopped, and the mixture was stirred at a constant temperature for 1h. The mixture was then aged at room temperature for 12h. The gel was washed with pure water until the pH reached approximately 7, and then washed twice with anhydrous ethanol to remove the water, yielding a modified gel. The modified gel was then heated in air to 105℃ at a rate of 5℃ / min and dried to obtain a dry gel. The dry gel was ground and then calcined at 300℃ for 1.5h to obtain a modified carrier.

[0041] (2) Preparation of potassium ferrate: Dissolve 100g of ferric chloride in water to prepare a 30% ferric chloride solution, transfer it to a round-bottom flask, and continue stirring at 300rpm. Then, add about 242g of liquid alkali dropwise at a rate of 5mL / min. After the addition is complete, filter the solution. The filter cake is a semi-solid ferric hydroxide.

[0042] Approximately 322g of sodium hypochlorite with 20% available chlorine was placed in a flask and stirred at 250 rpm. 68g of potassium hydroxide tablets were added and dissolved, maintaining the temperature below 30℃. After complete dissolution, the prepared ferric hydroxide semi-solid was added all at once, and the stirring speed was increased to 400 rpm. Once the mixture was homogeneous (with no obvious lumps of solid in the system), the remaining 158g of potassium hydroxide tablets was added. The stirring speed was kept constant, and the mixture was stirred at 40℃ for 20 minutes. The mixture was then cooled to 0℃ and filtered using a No. 2 sintered glass funnel to obtain a filter cake. This cake was then vacuum-dried at 60℃ for 2 hours to obtain crude potassium ferrate. The yield was 92.38%, and the content was 40.31% (the ratio of potassium ferrate in the product to the theoretical value, which has the same meaning below).

[0043] (3) Preparation of potassium ferrate composite material: The crude potassium ferrate from step (2) was added to a 3M potassium hydroxide solution and stirred at 800 rpm to dissolve. The mass ratio of the crude potassium ferrate to the 3M potassium hydroxide solution was 1:20. After dissolution, the modified carrier prepared in step (1) was added, wherein the mass ratio of the crude potassium ferrate to the modified carrier was 1:3. At 0℃, 1.2 W / cm 2 Under ultrasonic conditions, the mixture was stirred at 800 rpm for 40 min. After stirring, potassium hydroxide solid was added until saturated. The mixture was then kept at a constant temperature for 30 min and filtered. The filter cake was washed with anhydrous ethanol and then dried under vacuum at 40℃ to obtain the potassium ferrate composite material.

[0044] (4) Preparation of potassium ferrate bottom enrichment slow release agent: The potassium ferrate composite material prepared in step (3) is ground and passed through a 32-mesh sieve. After sieving, it is mixed with magnesium silicate fine powder with a particle size of 8μm at 800rpm for 10min. The mass of magnesium silicate fine powder is 0.7% of the mass of potassium ferrate bottom enrichment slow release agent. After mixing, it is first pre-compressed at a pressure of 0.4MPa, and then the pressure is gradually increased to 0.8MPa for 20s (pre-compression is gradually increased to form the product). Potassium ferrate bottom enrichment slow release agent is obtained and is denoted as L1.

[0045] Example 2:

[0046] (1) Preparation of modified carrier: 100g of 8% (3.0 modulus) water glass solution was added to a round-bottom flask. 0.16g of polyethylene glycol 6000 was added while stirring at 800rpm. The mixture was preheated to 75℃ and stirred at 800rpm for 20min. Then, 0.032g of lithium hydroxide was added, and the mixture was stirred at 800rpm for 25min at a constant temperature. Next, 1M acetic acid aqueous solution was added dropwise at a rate of 3mL / min until the pH reached 4.5. The addition of acetic acid aqueous solution was stopped, and the mixture was stirred at a constant temperature for 1h. The mixture was then aged at room temperature for 12h. The gel was washed with pure water until the pH reached approximately 7, and then washed twice with anhydrous ethanol to remove the water, yielding a modified gel. The modified gel was dried in air at a heating rate of 8℃ / min to 105℃ to obtain a dry gel. The dry gel was ground and then calcined at 300℃ for 1.5h to obtain a modified carrier.

[0047] (2) Preparation of potassium ferrate: Dissolve 100g of ferric chloride in water to prepare a 20% ferric chloride solution, transfer it to a round-bottom flask, and continue stirring at 300rpm. Then, add about 280g of liquid alkali dropwise at a rate of 5mL / min. After the addition is complete, filter the solution. The filter cake is a semi-solid ferric hydroxide.

[0048] Approximately 322g of sodium hypochlorite with 20% available chlorine was placed in a flask and stirred at 250 rpm. 84.94g of potassium hydroxide flakes were added and dissolved, maintaining the temperature below 30℃. After complete dissolution, the prepared ferric hydroxide semi-solid was added all at once, and the stirring speed was increased to 400 rpm. Once the mixture was homogeneous (with no obvious lumps of solid in the system), the remaining 191.54g of potassium hydroxide flakes was added. The stirring speed was kept constant, and the mixture was stirred at 40℃ for 20 minutes. The mixture was then cooled to 0℃ and filtered using a No. 2 sintered glass funnel to obtain a filter cake. This cake was then dried under vacuum at 60℃ for 2 hours to obtain crude potassium ferrate. The yield was 95.10%, and the content was 40.06%.

[0049] (3) Preparation of potassium ferrate composite material: The crude potassium ferrate from step (2) was added to a 3M potassium hydroxide solution and stirred at 800 rpm to dissolve. The mass ratio of the crude potassium ferrate to the 3M potassium hydroxide solution was 1:15. After dissolution, the modified carrier prepared in step (1) was added, wherein the mass ratio of the crude potassium ferrate to the modified carrier was 1:3. At 0℃, 1.2 W / cm 2 Under ultrasonic conditions, the mixture was stirred at 800 rpm for 40 min. After stirring, potassium hydroxide solid was added until saturated. The mixture was then kept at a constant temperature for 30 min and filtered. The filter cake was washed with anhydrous ethanol and then dried under vacuum at 40℃ to obtain the potassium ferrate composite material.

[0050] (4) Preparation of potassium ferrate bottom enrichment slow release agent: The potassium ferrate composite material prepared in step (3) is ground and passed through a 32-mesh sieve. After sieving, it is mixed with magnesium silicate fine powder with a particle size of 8μm at 800rpm for 10min. The mass of magnesium silicate fine powder is 0.7% of the mass of potassium ferrate bottom enrichment slow release agent. After mixing, it is first pre-compressed at a pressure of 0.3MPa, and then the pressure is gradually increased to 1MPa for 25s (pre-compression is gradually increased to form the product). Potassium ferrate bottom enrichment slow release agent is obtained and is denoted as L2.

[0051] Example 3:

[0052] The difference between this embodiment and Embodiment 1 is that in step (1), the raw materials are: 100g of water glass solution with a modulus of 3.0 and a mass fraction of 6%, 0.12g of polyethylene glycol 6000, and 0.03g of lithium hydroxide. In step (2), the raw materials are: 100g of ferric chloride prepared into a 25% ferric chloride solution, and 63.27g of potassium hydroxide added initially, for a total mass of 210.9g of potassium hydroxide. The final product is a potassium ferrate bottom-enrichment slow-release agent, designated L3. The yield of crude potassium ferrate was 91.12%, and the content was 39.92%.

[0053] Example 4:

[0054] The difference between this embodiment and embodiment 1 is that in step (3), the ultrasonic temperature is changed to 30°C, and the potassium ferrate bottom-enriched sustained-release agent is finally obtained, which is denoted as L4.

[0055] Example 5:

[0056] The difference between this embodiment and embodiment 1 is that in steps (1), (3), and (4), the stirring speed is 600 rpm; the potassium ferrate bottom-enriched slow-release agent is finally obtained and is denoted as L5.

[0057] Example 6:

[0058] The difference between this embodiment and embodiment 1 is that in step (3), the mass ratio of crude potassium ferrate to modified carrier is 1:1; the potassium ferrate bottom enrichment slow-release agent is finally obtained, which is denoted as L6.

[0059] Example 7:

[0060] The difference between this embodiment and embodiment 1 is that in step (3), the mass ratio of crude potassium ferrate to modified carrier is 1:4; the potassium ferrate bottom enrichment slow-release agent is finally obtained, which is denoted as L7.

[0061] Example 8:

[0062] The difference between this embodiment and embodiment 1 is that in step (4), 1% magnesium silicate fine powder of the same mass as the potassium ferrate bottom-enriched slow-release agent is added to finally obtain the potassium ferrate bottom-enriched slow-release agent, which is denoted as L8.

[0063] Example 9:

[0064] The difference between this embodiment and embodiment 1 is that in step (4), 0.8% of magnesium silicate fine powder with a mass equal to that of potassium ferrate bottom-enriched slow-release agent is added to finally obtain potassium ferrate bottom-enriched slow-release agent, denoted as L9.

[0065] The following is Comparative Example 1 with a water glass modulus of 2.0: The difference between this comparative example and Example 1 is that in step (1), the modulus of water glass is 2.0, and the potassium ferrate bottom-enriched slow-release agent is finally obtained, denoted as D1.

[0066] The following is Comparative Example 2 without the addition of lithium hydroxide: The difference between this comparative example and Example 1 is that lithium hydroxide is not added in step (1), and potassium ferrate bottom enrichment slow-release agent is finally obtained, which is denoted as D2.

[0067] The following is Comparative Example 3, which shows the modified gel being dried: The difference between this comparative example and Example 1 is that in step (1), the modified gel was directly placed in an oven at 105°C to dry, and the potassium ferrate bottom-enriched sustained-release agent was finally obtained, denoted as D3.

[0068] The following is Comparative Example 4, which uses traditional methods to prepare potassium ferrate: The difference between this comparative example and Example 1 is that the method for preparing the crude potassium ferrate obtained in step (2) is as follows: Sodium hypochlorite with a concentration of 1.476 mol / L and excess sodium hydroxide were mixed to form a first mixed solution. Ferric nitrate solid was slowly added to the first mixed solution while stirring slowly, and the reaction temperature was controlled at 24-30℃. After the reaction continued for more than 1.5 hours, the solution was filtered. Potassium hydroxide solid was added to the filtrate in excess while stirring slowly. Simultaneously, the ambient temperature was adjusted to 0℃. After the reaction was complete, the solution turned dark purple. The solution was filtered, and the filter cake was vacuum dried to obtain crude potassium ferrate. The yield of potassium ferrate was 45.13%, and the content was 19.16%.

[0069] The final product was potassium ferrate bottom-enriched slow-release agent, denoted as D4.

[0070] The following is Comparative Example 5 using externally purchased ferric hydroxide: The difference between this comparative example and Example 1 is that the iron hydroxide semi-solid prepared in step (2) is replaced with iron hydroxide purchased externally, and the potassium ferrate bottom enrichment slow-release agent is finally obtained, which is denoted as D5.

[0071] The following is Comparative Example 6, which involves directly compressing the prepared crude potassium ferrate into tablets: This comparative example differs from Example 1 in that steps (1) and (3) are omitted; instead, the crude potassium ferrate from step (2) is directly compressed into tablets. The resulting potassium ferrate bottom-enriched sustained-release agent is denoted as D6.

[0072] The following is Comparative Example 7: Tableting without pre-compression. The difference between this comparative example and Example 1 is that in step (4), no pre-compression is performed, and the tablets are directly compressed to obtain potassium ferrate bottom-enriched sustained-release agent, which is denoted as D7.

[0073] The following is Comparative Example 8 without the addition of a bottom-accumulating agent: The difference between this comparative example and Example 1 is that in step (4), magnesium silicate fine powder is not added, and potassium ferrate bottom enrichment slow release agent is finally obtained, which is denoted as D8.

[0074] Test Example 1: The potassium ferrate bottom-enriched slow-release agents prepared in Examples 1-9 and the bottom-enriched slow-release agents involved in Comparative Examples 1-8 were subjected to performance tests, and the test contents are as follows: (1) Detection of the specific surface area of ​​the modified carrier BET; (2) Detection of the release time of the bottom-accumulating slow-release agent potassium ferrate: Take 2g of the bottom-enriched sustained-release agent and add it to 200mL of pure water. Take samples every two minutes and determine the ferrate concentration by chromite titration. Record the time when the ferrate release finally stops, which is called the release time.

[0075] (3) Decomposition rate test of potassium ferrate after 30 days: The bottom-enriched slow-release agent prepared in the above example was placed in air, and the decomposition rate of potassium ferrate was measured after 30 days.

[0076] The performance test results are shown in Table 1.

[0077] .

[0078] Test Example 2: The bottom-accumulation effect was determined by taking 2g each of the bottom-accumulation slow-release agent from Example 1 and the slow-release agent from Comparative Example 8 without added magnesium silicate powder, placing them in beakers containing 250mL of pure water, and observing after complete dissolution. The color distribution was observed using the fact that potassium ferrate dissolves in water to produce a distinct purple color; the results are shown in [the table below]. Figure 1 .

[0079] Figure 1 In the image, the left side shows the dissolution results of the slow-release agent without added magnesium silicate powder in Comparative Example 8, while the right side shows the dissolution results of the bottom-enriched slow-release agent involved in Example 1.

[0080] Depend on Figure 1 It can be seen that the slow-release agent with added magnesium silicate fine powder is darker in color and mainly concentrated at the bottom of the beaker, while the slow-release agent without added magnesium silicate fine powder is lighter in color and dispersed throughout the beaker. This indicates that after adding magnesium silicate fine powder, the slow-release agent can greatly increase the concentration of potassium ferrate at the bottom, thus playing a targeted role.

[0081] Test Example 3: The bottom-accumulating slow-release agents involved in Examples 1-9 and Comparative Examples 1-8 were used to improve the bottom sediment of aquaculture ponds, and the removal rate of harmful substances was measured, specifically including: Take 20g of the same sludge and place it in a beaker containing 250mL of pure water. Stir well and let it stand to settle. Add one granule of the bottom enrichment slow-release agent prepared in the above example. After it is completely dissolved, react for 10min. Remove the upper liquid and take the lower sludge mixture. Centrifuge at high speed and take the supernatant for testing. The results are shown in Table 2.

[0082] .

[0083] The results above demonstrate that the potassium ferrate bottom-accumulating and slow-release agent prepared by the method of this invention exhibits ideal bottom-accumulation, slow release, and stability, effectively removing COD, BOD, H2S, and ammonia nitrogen from pond bottom sludge, with removal rates reaching approximately 93%, 85%, 98%, and 83%, respectively. Compared to traditional bottom sediment improvers and purifiers, it features targeted and slow-release properties.

Claims

1. A method for preparing a potassium ferrate bottom-up enriched slow release agent, characterized by: The preparation steps are as follows: S1: polyethylene glycol is added to the water glass solution, heated and stirred until dissolved, then lithium hydroxide is added and stirred until dissolved, acidified, then aged at room temperature, and the modified gel obtained after aging is washed, slowly dried, ground and calcined to obtain a modified carrier; S2: a certain amount of potassium hydroxide is added to sodium hypochlorite for first dissolution, iron hydroxide semi-solid is added for second dissolution, then potassium hydroxide is continuously added, and third dissolution is carried out under constant temperature stirring, then cooled, filtered and dried to obtain a crude potassium ferrate product; S3: the crude potassium ferrate product obtained in step S2 is added to a 3M potassium hydroxide solution, stirred to dissolve, then the modified carrier obtained in step S1 is added, and second stirring is carried out under ultrasonic conditions, then potassium hydroxide solid is added to saturation, and after incubation and standing, the filter cake is washed with anhydrous ethanol and dried to obtain a potassium ferrate composite material; S4: the potassium ferrate composite material obtained in step S3 is ground, sieved and mixed with a bottom enrichment agent, and after mixing, a potassium ferrate bottom enrichment slow-release agent is obtained by tabletting.

2. The method for preparing a high-potassium ferrate bottom-up enrichment sustained-release agent according to claim 1, characterized in that: In the S1 step, the modulus of the water glass is 3.0-3.2, and the mass concentration is 5-8%; the amount of lithium hydroxide added is 0.2-0.5% of the mass of sodium silicate solute in the water glass solution, and the amount of polyethylene glycol added is 1-3% of the mass of sodium silicate solute in the water glass; in the S2 step, the mass of potassium hydroxide added for the first time is 30-40% of the total mass of potassium hydroxide; in the S3 step, the effective chlorine in sodium hypochlorite is 15-20%; the mass ratio of crude potassium ferrate to 3M potassium hydroxide solution is 1:15-20; and the mass ratio of crude potassium ferrate to modified carrier is 1:3-4.

3. The method for preparing a high-potassium ferrate bottom-up enrichment sustained-release agent according to claim 1, characterized in that: In the S4 step, the bottom enrichment agent is magnesium silicate fine powder with a particle size of 5-8 μm; and the amount of bottom enrichment agent added is 0.7%-1% of the mass of the potassium ferrate composite material.

4. The method for preparing a high-potassium ferrate bottom-up enrichment sustained-release agent according to claim 1, characterized in that: In the S2 step, the preparation method of the iron hydroxide semi-solid is as follows: iron chloride solution is placed in a flask, then liquid alkali is slowly added for reaction, the reaction is completed by filtration, and the filter cake is the iron hydroxide semi-solid; the molar ratio of iron chloride to total potassium hydroxide is 1:6-8; and the molar ratio of iron chloride to sodium hypochlorite is 1:1.5-1.

8.

5. The method for preparing a high-potassium ferrate bottom-up enrichment slow-release agent according to claim 4, characterized in that: The mass fraction of the iron chloride solution is 20-30%; the liquid alkali is sodium hydroxide with a mass concentration of 30%, and the molar ratio of iron chloride to sodium hydroxide in the liquid alkali is 1:3-3.

5.

6. The method for preparing a high potassium ferrate bottom-up enriched slow release agent according to claim 1, characterized in that: The specific operation of slowly heating and drying is as follows: the washed modified gel is slowly heated to 105°C at a rate of 5-8°C / min in air to dry to obtain a dry gel; The calcination temperature of the ground dry gel is 200-400°C, and the calcination time is 1-2 h.

7. The method for preparing a high potassium ferrate bottom-up enriched slow release agent according to claim 1, characterized in that: The acidification operation in the S1 step is specifically: slowly adding an aqueous acetic acid solution until the pH is 4.5, and then continuing constant temperature stirring for 1-1.5 h, the acidification temperature is 75-80℃; the aging time is 12-16 h; the dissolution temperature of the first dissolution in the S2 step is 0-30℃, the dissolution temperature of the third dissolution is 40-60℃, the dissolution time is 20-40 min; the cooling temperature is-5-0℃; the drying condition is vacuum drying at 60℃ for 1-3 h; the S3 step is all operated at 0-5℃; in the S3 step, the ultrasonic frequency is 40-59 kHz, the power is 100-250 w; the ultrasonic time is 20-40 min.

8. The method for preparing a high potassium ferrate bottom-up enriched slow release agent according to claim 1, characterized in that: The specific steps of the tabletting operation in the S4 step are: first pre-pressing under a pressure of 0.3-0.5 Mpa, then gradually increasing the pressure to 0.5-1 Mpa, and the total tabletting time is 15-30 s.

9. A potassium ferrate based bottom-up enriched slow release agent, characterized in that: The high-iron potassium ferrate bottom-up enrichment slow-release agent prepared by the preparation method of any one of claims 1-8.

10. The use of the high-iron potassium ferrate bottom-up enrichment slow-release agent according to claim 9 in improving the bottom quality of a pond.

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