Preparation method of slow-release organic chelated iron fertilizer

Abstract

The invention relates to the technical field of slow-release organic fertilizers, and particularly discloses a preparation method of a slow-release organic chelated iron fertilizer. Comprising the following steps: 1, completely dissolving a titanium dioxide byproduct ferrous sulfate heptahydrate in pure water in an inert atmosphere, adding iron powder, and filtering to obtain a ferrous salt solution; 2, under the stirring condition, lignosulfonate is added into pure water to be completely dissolved, and an organic salt solution is prepared; step 3, adding the ferrite solution obtained in the step 1 into an organic salt solution in an inert atmosphere to obtain a pre-complexation solution; step 4, dropwise adding dilute alkali liquor into the pre-complexing solution under stirring to adjust the pH value, and keeping stirring for 20-30 minutes to obtain a ferrous lignosulfonate solution; and step 5, putting the carrier with the adsorption gaps and the cavity inside into a ferrous lignosulfonate solution, vacuumizing to fully infiltrate the inside of the carrier, taking out, filtering, and drying to obtain the slow-release organic chelated iron fertilizer. The technology fills the technical blank that chelated iron fertilizer prepared in the prior art can only be sprayed and is not suitable for being used as base fertilizer.

Description

Technical Field

[0001] This application relates to the field of slow-release organic fertilizer technology, and specifically discloses a method for preparing slow-release organic chelated iron fertilizer. Background Technology

[0002] Ferrous sulfate heptahydrate (FeSO4·7H2O), a byproduct of titanium dioxide production via the sulfuric acid process, has low direct sales value due to its high content of impurity ions such as manganese, magnesium, and zinc. Therefore, there is an urgent need to find new ways to utilize its value.

[0003] In agriculture, in addition to major nutrients such as phosphorus, ammonium, and potassium, crops also require some micronutrients for healthy growth and development. Although the required amounts are relatively small, they are crucial for plant physiological functions. A deficiency in any micronutrient can lead to stunted growth, reduced yield, or even crop failure. For example, iron deficiency in crops can hinder chlorophyll synthesis (chlorosis), reduce photosynthetic efficiency, cause abnormal respiration and energy metabolism, decrease enzyme activity, and restrict root development, significantly impacting crop yield and quality. Furthermore, when traditional inorganic salt fertilizers (such as ferrous sulfate, zinc sulfate, and calcium chloride) are applied to the soil, the metal ions easily combine with phosphate, carbonate, or soil colloids to form insoluble precipitates (such as calcium phosphate and zinc carbonate), leading to a sharp decrease in the availability of micronutrients. Inorganic salt ions are also easily leached or fixed in the soil; the actual absorption rate by crops is less than 10%. To address the problem of insufficient micronutrient supply to crops by traditional inorganic salt fertilizers, chelated fertilizers have emerged in agriculture. Chelated fertilizers utilize chelating agents to chelate a certain amount of micronutrients. After application, the chelating agent effectively binds these metal ions in the soil to prevent their loss, while also releasing them in appropriate amounts when necessary. This balances the nutrient supply among roots, stems, leaves, flowers, and fruits, promoting robust plant growth. It also enhances photosynthesis and nutrient complementarity, promotes root development, balances various nutrients, and plays a coordinating role, thereby improving plant disease resistance and yield.

[0004] Ferrous sulfate heptahydrate, a byproduct of titanium dioxide production, contains not only Fe, essential for crop growth, but also trace elements such as Mg, Mn, Zn, and Cu. However, when ferrous sulfate heptahydrate is directly used as fertilizer in alkaline soils, Fe... 2 ⁺ Easily oxidized into ineffective Fe 3+The effectiveness of ferrous sulfate decreases. Therefore, preparing it as a chelated fertilizer becomes the best option. Most techniques for preparing ferrous sulfate as a chelated fertilizer use organic chemical substances and organic extractants, which are costly and environmentally unfriendly. For example, patent CN118955312A discloses a one-pot method for preparing o,o-EDDHA-Fe, successfully producing o,o-EDDHA-Fe with an iron content of 7%-8% and insoluble matter ≤0.05%, offering advantages such as short preparation time and high ortho-position value. Another example is patent CN114804979A, which discloses an organic chelated iron fertilizer and its preparation process. This involves mixing, pulverizing, and drying 30-50 parts of ferrous sulfate hydrate, 10-20 parts of mineral-derived potassium humate, 20-40 parts of ammonium sulfate, 8-10 parts of urea, and 1-10 parts of potassium citrate to obtain the organic chelated iron fertilizer. Spraying this fertilizer has a positive impact on the appearance, growth, fruit quality, and yield of crops.

[0005] While the aforementioned chelated iron fertilizers can coordinate and fix ferrous elements, making them less prone to leaching and soil fixation compared to inorganic iron fertilizers, thus effectively enhancing their fertilizer efficacy, they all directly coordinate the chelating agent with metal particles to form chelated fertilizers. This method makes the chelated fertilizers susceptible to the influence of the soil conditions and environment (e.g., when the concentration of the target ion in the soil solution is below the critical value, the chelate dissociates metal ions towards the low concentration side according to Le Chatelier's principle, and the dissociated metal ions are easily lost). The duration of their fertilizer effect is relatively short, making them suitable only for foliar spraying and not for use as base fertilizer. Therefore, the industry urgently needs a method for preparing slow-release chelated iron fertilizers with a longer-lasting fertilizer effect suitable for use as base fertilizer. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing slow-release organic chelated iron fertilizer, which fills the technical gap in the prior art where chelated iron fertilizer can only be sprayed and is not suitable for use as a base fertilizer.

[0007] To solve the above problems, the technical solution adopted by the present invention is as follows: a method for preparing a slow-release organic chelated iron fertilizer, comprising the following steps: Step 1: Under an inert atmosphere, dissolve the titanium dioxide byproduct ferrous sulfate heptahydrate in pure water to ensure that the iron salt is completely dissolved. Add iron powder and stir to reduce ferric iron. Filter and take the filtrate to obtain a ferrous salt solution. Step 2: Under stirring conditions, add lignin sulfonate to pure water to ensure complete dissolution and prepare an organic salt solution; Step 3: Under an inert atmosphere, add the ferrous salt solution obtained in Step 1 to the organic salt solution to obtain a pre-complexed solution; Step 4: While stirring continuously, add dilute alkali solution dropwise to the pre-complexed solution to adjust the pH. After the addition is complete, continue stirring for 20-30 minutes to obtain ferrous lignosulfonate solution. Step 5: Place the carrier with internal adsorption pores and cavities into a ferrous lignosulfonate solution, and evacuate the container to allow the ferrous lignosulfonate solution to fully wet the interior of the carrier. The carrier is then adsorbed and fixed inside by hydrogen bonds and capillary forces. After filtration, the container is heated to 30-60℃ and dried to obtain a slow-release organic chelated iron fertilizer.

[0008] The beneficial effects of this implementation plan are as follows: 1. Existing technologies all directly coordinate chelating agents with metal particles to form chelated fertilizers. This method has a short duration of fertilizer effect and can only be applied as a foliar spray, not as a base fertilizer. This application innovatively adsorbs ferrous lignin sulfonate, an organic chelated iron fertilizer, into carriers such as biochar, bentonite, and vermiculite, successfully preparing a slow-release organic iron fertilizer with a longer-lasting effect, which can be applied as a base fertilizer.

[0009] 2. This application uses a repeated vacuum impregnation method to fix the organic complex iron fertilizer inside the activated biochar, bentonite, vermiculite and other carriers by utilizing hydrogen bonds and capillary forces. This can not only effectively alleviate problems such as ferrous ion oxidation and soil consolidation, but also play a slow-release role.

[0010] 3. This application fully utilizes the characteristics of ferrous sulfate heptahydrate, a by-product of titanium dioxide, which contains impurity ions such as Mg, Mn, Zn, and Cu. Using it as a raw material to prepare iron fertilizer can effectively provide nutrients to plants without additional purification, while also effectively enhancing the market economic value of ferrous sulfate heptahydrate, a by-product of titanium dioxide.

[0011] Furthermore, the carrier includes activated biochar, bentonite, and vermiculite, and the activating agents used in the activation process of the activated biochar, bentonite, and vermiculite include KOH, NaOH, HCl, and H2SO4.

[0012] Furthermore, the pure water used in steps 1 and 2 is oxygen-free pure water.

[0013] Furthermore, the lignin sulfonate is any one of sodium lignin sulfonate, calcium lignin sulfonate, magnesium lignin sulfonate, and ammonium lignin sulfonate.

[0014] Furthermore, the lignin sulfonate is in powder form.

[0015] Furthermore, in step 5, the vacuuming and drying process is carried out using a vacuum oven, and the vacuuming process needs to be repeated 3-12 times.

[0016] Furthermore, in step 4, KOH, NaOH, and ammonia are used to adjust the pH value.

[0017] Furthermore, in step 3, before adding the iron salt to the organic salt solution, an synergist needs to be added to the iron salt solution and stirred evenly. The synergist is at least one of sodium salicylate, citric acid, and ascorbic acid.

[0018] Furthermore, the concentration of the iron salt in step 1 is 1-1.2 mol / L.

[0019] Furthermore, in step 4, the pH is adjusted to 5-6.5.

[0020] Attached image description.

[0021] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0022] The following detailed description provides further details on specific embodiments, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the technical means used in the following embodiments are conventional means well known to those skilled in the art; the experimental methods used are all conventional methods; and the materials and reagents used are all commercially available.

[0023] Overview of the plan: S1: The carrier (biochar, bentonite, vermiculite) is activated using activating agents (KOH, NaOH, HCl, H2SO4) to obtain the activated carrier; S2: Under an inert atmosphere, dissolve ferrous sulfate heptahydrate, a byproduct of titanium dioxide production, in an appropriate amount of oxygen-free pure water to ensure complete dissolution of the ferrous salt. Add an appropriate amount of iron powder and stir to reduce ferric iron. Filter the solution and add an appropriate amount of synergist (sodium salicylate, citric acid, ascorbic acid) to obtain a ferrous salt solution (ferrous ion concentration 1-1.2 mol / L).

[0024] S3: Under stirring conditions, slowly add lignin sulfonate (sodium lignin sulfonate, calcium lignin sulfonate, magnesium lignin sulfonate, ammonium lignin sulfonate) powder to an appropriate amount of oxygen-free pure water to ensure complete dissolution and prepare an organic salt solution.

[0025] S4: While stirring, add the iron salt solution obtained in S2 to the organic complex salt solution obtained in S3 to obtain a pre-complexed solution.

[0026] S5: While continuously stirring, very slowly add dilute alkali solution to the pre-complexed solution to adjust the pH (5-6.5). After the addition is complete, continue stirring for 20-30 minutes to obtain ferrous lignosulfonate solution. S6: Place the activated carrier obtained in S1 into the pre-complexed solution in S5, mix thoroughly, and place in a vacuum oven for repeated vacuuming (3-12 times) to allow the ferrous lignin sulfonate solution to fully wet the interior of the activated carrier. After filtration, return to the vacuum oven and heat to 30-60℃ for drying to obtain slow-release organic chelated iron fertilizer.

[0027] Implementation, for example, attached Figure 1 As shown.

[0028] Example 1 Activate and dry 30g of biochar with 1 mol / L NaOH solution for later use. Under an inert atmosphere, dissolve 278g of titanium dioxide byproduct ferrous sulfate heptahydrate in 722g of oxygen-free pure water, add 2g of iron powder to reduce the oxidized iron ions, filter, add 1.8g of sodium salicylate and 1.2g of citric acid to the filtrate and stir evenly to prepare a ferrous solution of about 1 mol / L for later use. Dissolve 120g of sodium lignosulfonate in 2500g of water, and add all the ferrous solution while stirring. After mixing evenly, add dilute ammonia to adjust the pH to 6, stir for 20 minutes, add activated biochar and stir evenly, place in a vacuum oven (45℃, 5h) and repeatedly vacuum (8 times) to ensure that the mixed solution fully wets the interior of the activated carrier and adsorbs ferrous lignosulfonate into the pores inside the carrier. Remove, filter and dry, and return to the vacuum oven. Heat to 30℃ to obtain slow-release organic chelated iron fertilizer lignosulfonic acid-Fe.

[0029] Example 2 45g of bentonite was activated and dried with 1.5mol / L H2SO4 solution and set aside for later use. Under an inert atmosphere, 333g of ferrous sulfate heptahydrate (a byproduct of titanium dioxide production) was dissolved in 667g of pure water. 2.5g of iron powder was added to reduce the oxidized iron ions. After filtration, 3g of sodium salicylate and 5g of ascorbic acid were added to the filtrate and stirred until homogeneous, preparing a ferrous solution of approximately 1.2mol / L for later use. 140g of magnesium lignosulfonate was dissolved in 3000g of water. While stirring, all the ferrous solution was added. After mixing evenly, dilute sodium hydroxide solution was added to adjust the pH to 5.5. The mixture was stirred for 25 minutes, and then activated bentonite was added and stirred evenly. The mixture was placed in a vacuum oven (30℃, 5h) and repeatedly vacuumed (10 times) to ensure that the mixed solution fully impregnates the interior of the activated carrier, adsorbing the ferrous lignosulfonate into the pores inside the carrier. After filtration and drying, the mixture was returned to the vacuum oven and heated to 45℃ to obtain the slow-release organic chelated iron fertilizer lignosulfonic acid-Fe.

[0030] Example 3 15g of biochar was activated with 1 mol / L NaOH solution and then dried; 15g of bentonite was activated with 1.5 mol / L H2SO4 solution and then dried; and 15g of bentonite was activated with 1 mol / L H2SO4 solution and then dried. After activation with mol / L KOH solution, dried vermiculite was mixed in a 1:1:1 ratio and set aside. Under an inert atmosphere, 300g of titanium dioxide byproduct ferrous sulfate heptahydrate was dissolved in 700g of oxygen-free pure water. 2g of iron powder was added to reduce the oxidized iron ions. After filtration, 1.2g of citric acid and 5g of ascorbic acid were added to the filtrate and stirred until homogeneous to prepare a ferrous solution for later use. Ammonium lignosulfonate was dissolved in water and added to the entire ferrous solution while stirring. After mixing evenly, dilute potassium hydroxide solution was added to adjust the pH to 6.5. The mixture was stirred for 30 minutes, and an activation carrier was added. The mixture was placed in a vacuum oven (30℃, 7h) and repeatedly vacuumed (8 times) to ensure that the mixed solution fully wetted the interior of the activation carrier and adsorbed the ferrous lignosulfonate into the pores inside the carrier. After filtration, the mixture was returned to the vacuum oven and dried at 60℃ to obtain the slow-release organic chelated iron fertilizer lignosulfonic acid-Fe.

[0031] Comparative Example 1 Activate and dry 30g of biochar with 1 mol / L NaOH solution for later use; under an inert atmosphere, dissolve 278g of titanium dioxide by-product ferrous sulfate heptahydrate in 722g of oxygen-free pure water, add 2g of iron powder to reduce the oxidized iron ions, filter, add 1.8g of sodium salicylate and 1.2g of citric acid to the filtrate and stir evenly to prepare an approximately 1mol / L ferrous solution for later use; dissolve 120g of sodium lignin sulfonate in 2500g of water, and add the entire ferrous solution while stirring. After mixing evenly, add dilute ammonia water to adjust the pH to 6, and stir for 20 minutes to obtain the organic chelated iron fertilizer lignin sulfonate-Fe.

[0032] Comparative Example 2 Activate and dry 45g of bentonite with 1.5mol / L H2SO4 solution and set aside for later use; under an inert atmosphere, dissolve 333g of titanium dioxide by-product ferrous sulfate heptahydrate in 667g of pure water, add 2.5g of iron powder to reduce the oxidized iron ions, filter, add 3g of sodium salicylate and 5g of ascorbic acid to the filtrate and stir well to prepare a ferrous solution of about 1.2mol / L for later use; dissolve 140g of magnesium lignin sulfonate in 3000g of water, add all the ferrous solution while stirring, mix well, add dilute sodium hydroxide solution to adjust the pH to 5.5, stir for 25 minutes to obtain the organic chelated iron fertilizer lignin sulfonate-Fe.

[0033] Comparative Example 3 15g of biochar was activated and dried with 1 mol / L NaOH solution, and 15g of bentonite was activated and dried with 1.5 mol / L H2SO4 solution. These were then mixed with 15g of vermiculite activated and dried with 1 mol / L KOH solution in a 1:1:1 ratio and set aside for later use. Under an inert atmosphere, 300g of ferrous sulfate heptahydrate (a byproduct of titanium dioxide production) was dissolved in 700g of oxygen-free pure water. 2g of iron powder was added to reduce the oxidized iron ions. After filtration, 1.2g of citric acid and 5g of ascorbic acid were added to the filtrate and stirred until homogeneous to prepare a ferrous solution for later use. Ammonium lignin sulfonate was dissolved in water and added to the entire ferrous solution while stirring. After mixing thoroughly, dilute potassium hydroxide solution was added to adjust the pH to 6.5, and the mixture was stirred for 30 minutes to obtain the organic chelated iron fertilizer lignin sulfonate-Fe.

[0034] The data on fertilizer release rate and residual Fe ion oxidation rate of each sample in neutral soil (6.5-7.5) over time are shown in Tables 1 and 2. The results indicate that loading the organic chelated iron fertilizer lignin sulfonate-Fe into materials such as biochar, bentonite, and vermiculite can effectively prolong its fertilizer release time, ensuring continuous release during the rapid growth period of plants (30-80 days), which is beneficial for effective plant absorption. Furthermore, this design helps reduce the oxidation rate of ferrous ions; after 30 days of fertilization, the residual Fe ion oxidation rate is <20%, far lower than the oxidation rate of direct application of lignin sulfonate-Fe.

[0035] Table 1. Fertilizer release rate of each sample in neutral soil (6.5-7.5) over time.

[0036] Table 2. Changes in residual Fe ion oxidation rate over time for each sample in neutral soil (6.5-7.5).

[0037] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing a slow-release organic chelated iron fertilizer, characterized in that: Includes the following steps: Step 1: Under an inert atmosphere, dissolve the titanium dioxide byproduct ferrous sulfate heptahydrate in pure water to ensure that the iron salt is completely dissolved. Add iron powder and stir to reduce ferric iron. Filter and collect the filtrate to obtain a ferrous salt solution. Step 2: Under stirring conditions, add lignin sulfonate to pure water to ensure complete dissolution and prepare an organic salt solution; Step 3: Under an inert atmosphere, add the ferrous salt solution obtained in Step 1 to the organic salt solution to obtain a pre-complexed solution; Step 4: While stirring continuously, add dilute alkali solution dropwise to the pre-complexed solution to adjust the pH. After the addition is complete, continue stirring for 20-30 minutes to obtain ferrous lignosulfonate solution. Step 5: Place the carrier with internal adsorption pores and cavities into a ferrous lignosulfonate solution, and evacuate the container to allow the ferrous lignosulfonate solution to fully wet the interior of the carrier. The carrier is then adsorbed and fixed inside by hydrogen bonds and capillary forces. After filtration, the container is heated to 30-60℃ and dried to obtain a slow-release organic chelated iron fertilizer.

2. The method for preparing the slow-release organic chelated iron fertilizer according to claim 1, characterized in that: The carrier includes activated biochar, bentonite, and vermiculite, and the activating agents used in the activation process of the activated biochar, bentonite, and vermiculite include KOH, NaOH, HCl, and H2SO4.

3. The method for preparing the slow-release organic chelated iron fertilizer according to claim 1, characterized in that: The pure water used in steps 1 and 2 is oxygen-free pure water.

4. The method for preparing the slow-release organic chelated iron fertilizer according to claim 1, characterized in that: The lignin sulfonate is any one of sodium lignin sulfonate, calcium lignin sulfonate, magnesium lignin sulfonate, and ammonium lignin sulfonate.

5. The method for preparing the slow-release organic chelated iron fertilizer according to claim 1, characterized in that: The lignin sulfonate is in powder form.

6. The method for preparing the slow-release organic chelated iron fertilizer according to claim 1, characterized in that: In step 5, the vacuuming and drying process is carried out using a vacuum oven, and the vacuuming process needs to be repeated 3-12 times.

7. The method for preparing the slow-release organic chelated iron fertilizer according to claim 1, characterized in that: In step 4, the pH value is adjusted using KOH, NaOH, and ammonia.

8. The method for preparing the slow-release organic chelated iron fertilizer according to claim 1, characterized in that: In step 3, before adding the iron salt to the organic salt solution, an synergist needs to be added to the iron salt solution and stirred evenly. The synergist is at least one of sodium salicylate, citric acid, and ascorbic acid.

9. The method for preparing the slow-release organic chelated iron fertilizer according to claim 1, characterized in that: The concentration of iron salt in step 1 is 1-1.2 mol / L.

10. The method for preparing the slow-release organic chelated iron fertilizer according to claim 1, characterized in that: In step 4, the pH is adjusted to 5-6.5.

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