Method for recovering and preparing fertilizer iron supplement additive from iron phosphate residue

Abstract

This invention discloses a method for preparing iron-supplementing fertilizer additives from recycled ferric phosphate slag, belonging to the field of fertilizer preparation technology. The method specifically includes the following steps: ferric phosphate slag is calcined, then leached in sulfuric acid to remove lithium ions, followed by leaching in sulfuric acid and hydrogen peroxide. Phosphoric acid is then removed by adsorption with an adsorbent, followed by reduction with iron powder. Finally, it is complexed with fulvic acid to obtain the iron-supplementing fertilizer additive. This invention further improves the purity and recovery of iron through calcination leaching and adsorption, thereby further enhancing its complexation with fulvic acid and synergistically increasing tomato yield.

Description

Technical Field

[0001] This invention relates to the field of fertilizer preparation technology, specifically to a method for preparing iron-supplementing fertilizer additives by recovering ferric phosphate slag. Background Technology

[0002] With the rapid development of the new energy industry, lithium iron phosphate has been widely used due to its significant advantages. However, after the first batch of lithium iron phosphate batteries are retired, the recycling and disposal of waste batteries has become a problem for the industry. During the recycling process, a large amount of iron phosphate slag will be generated through dismantling and other processes. Directly dumping or landfilling it will cause resource waste and environmental pollution. Therefore, efficient recycling of iron resources and high-value utilization have become the focus of research.

[0003] Currently, there are two main types of iron recovery technologies from lithium iron phosphate slag: pyrometallurgy and hydrometallurgy. Pyrometallurgy is energy-intensive, easily leads to iron oxidation and loss, and is difficult to destroy the stable crystal structure of lithium iron phosphate, affecting iron leaching efficiency. Although hydrometallurgy can improve the iron dissolution rate, it has problems such as phosphate ions combining with iron ions to form insoluble precipitates, resulting in a reduced iron recovery rate, and impurities in the leachate are difficult to remove completely, resulting in insufficient purity of the recovered iron product, which cannot meet the needs of high-value applications.

[0004] In agriculture, iron is an essential micronutrient for crop growth. Cash crops such as tomatoes are sensitive to iron deficiency, which can lead to yellowing leaves and reduced yield. However, most iron-supplementing fertilizers on the market exist in the form of ferrous sulfate and EDTA chelated iron. Ferrous sulfate is easily fixed into ineffective iron, resulting in low crop absorption and utilization. EDTA chelated iron has high production costs, and some products have insufficient chelation rates. At the same time, the iron source of iron-supplementing fertilizers mostly relies on industrial-grade chemical raw materials, and large-scale recovery of iron resources from solid waste such as waste lithium iron phosphate battery residue has not been achieved. The purity and quality of the recovered iron are difficult to meet the requirements of fertilizer production. Incomplete removal of impurities also leads to a decrease in the complexation efficiency between iron and chelating agents, resulting in insufficient effective iron content in fertilizers and limited effects on increasing crop yield.

[0005] In summary, traditional technologies suffer from low recovery rates and insufficient product purity in the iron recovery process of ferric phosphate slag, and face challenges such as low complexation efficiency, insufficient effective iron content, and limited yield-increasing effects in the preparation of iron-supplementing fertilizers. Developing relevant high-efficiency technologies has become a key direction. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing iron-supplementing fertilizer additives by recycling ferric phosphate slag, so as to solve the technical defects mentioned in the background art.

[0007] The objective of this invention can be achieved through the following technical solution: a method for preparing iron-supplementing fertilizer additives by recovering ferric phosphate slag, comprising the following steps:

[0008] S1. Place the ferric phosphate slag in a tube furnace and roast it in an air atmosphere at 600-700℃ for 2-3 hours. Then, immerse it in a sulfuric acid solution and leach it at 40-60℃ for 30-50 minutes. Filter the solution to obtain purified slag.

[0009] Reaction principle:

[0010] 12LiFePO4+ 3O2== 4Li3Fe2(PO4)3·2Fe2O3

[0011] 2Li3Fe2(PO4)3·2Fe2O3+ 3H2SO4== 3Li2SO4+ 6FePO4+ 3H2O

[0012] 2Li3Fe2(PO4)3·2Fe2O3+ 3H2SO4== Li2SO4+ 4FePO4+ Fe2O3+ 2LiHSO4+2LiH2SO4

[0013] 2Li3Fe2(PO4)3·2Fe2O3+ 2H2SO4== 2Li2SO4+ 4FePO4+ Fe2O3+ 2LiH2SO4

[0014] The LiFePO4 in the iron phosphate slag is roasted in air and reacts with oxygen to form Li3Fe2(PO4)3·2Fe2O3. The roasted product is then immersed in sulfuric acid solution. Li3Fe2(PO4)3·2Fe2O3 reacts with sulfuric acid to be converted into soluble lithium sulfate, lithium hydrogen sulfate and insoluble iron phosphate, iron oxide and other substances. After filtration, purified iron slag rich in iron phosphate and iron oxide can be obtained.

[0015] S2. Add the purified iron slag to a reaction vessel containing hydrogen peroxide and sulfuric acid solution, and stir at 50-70℃ for 1-2 hours to obtain an iron ion leachate.

[0016] Reaction principle:

[0017] 2FePO4+ 3H2SO4+ H2O2== Fe(SO4)3+ 2H3PO4+ 2H2O

[0018] When purified iron slag rich in ferric phosphate and ferric oxide is added to a mixed solution of hydrogen peroxide and sulfuric acid, on the one hand, ferric phosphate reacts with sulfuric acid and hydrogen peroxide. Hydrogen peroxide acts as an oxidant, promoting the conversion of ferric phosphate into soluble ferric sulfate, while generating phosphoric acid and water. On the other hand, ferric oxide reacts with sulfuric acid to generate ferric sulfate and water, ultimately allowing iron to exist in the solution in the form of ferric ions.

[0019] S3. Add adsorbent to the iron ion leaching solution, adsorb at 20-30℃ for 1-2 hours, filter, add elemental iron to the filtrate, stir at 50-60℃ for 40-50 minutes, filter, and obtain ferrous solution.

[0020] Reaction principle:

[0021] Fe 3+ + Fe == 2Fe 2+

[0022] When an adsorbent is added to the iron ion leaching solution, in this weakly acidic solution, the amino groups of triacetic acid on the adsorbent surface are protonated to form -NH3. + The carboxyl group dissociates into -COO ¯ , where -NH3 + Phosphate is specifically adsorbed onto the adsorbent surface through electrostatic attraction, while the carboxyl oxygen and amino nitrogen of triacetic acid can form hydrogen bonds with the hydroxyl groups of phosphate. Some phosphate groups are further immobilized through coordination, thus ensuring the adsorption of phosphate onto the adsorbent surface. 3+ In weakly acidic solutions, it mainly exists as hydrated iron ions. Its interaction with the functional groups on the adsorbent surface is much weaker than that of phosphate ions, so it remains in the solution. Filtration allows phosphate ions to react with Fe ions. 3+ After separation and adsorption, elemental iron is added to the filtrate. Iron acts as a reducing agent, removing Fe from the filtrate. 3+ Fe reduction 2+ .

[0023] S4. Add the ferrous solution to the fulvic acid solution and stir at 20-30℃ for 20-30 minutes. After post-treatment, the fertilizer iron supplement additive is obtained.

[0024] Reaction principle:

[0025] When ferrous solution is added to fulvic acid solution, the carboxyl and phenolic hydroxyl groups in fulvic acid molecules partially dissociate in solution, forming negatively charged -COO¯ and -O. - These sites, where oxygen atoms provide lone pairs of electrons, combine with ferrous ions through coordinate bonds to form stable water-soluble ferrous humic acid complexes, ultimately yielding a fertilizer iron supplement that can continuously provide plants with absorbable iron.

[0026] Furthermore, in step S1, the ratio of the amount of ferric phosphate residue to sulfuric acid solution is 1g:4-6mL, and the mass fraction of the sulfuric acid solution is 10%.

[0027] Furthermore, in step S2, the ratio of the amount of purified iron slag, hydrogen peroxide and sulfuric acid solution is 100g:35-45mL:400-500mL, and the mass fraction of the sulfuric acid solution is 25%.

[0028] Furthermore, in step S3, the ratio of the iron ion leachate, adsorbent, and elemental iron is 1L:10-20g:4-8g.

[0029] Furthermore, in step S4, the ratio of ferrous solution to fulvic acid solution is 1 mL: 2-3 mL, and the mass fraction of fulvic acid solution is 2.25%. The post-processing operation includes: after the reaction is completed, transferring the solution to a rotary flask, concentrating it at 40°C until there is no obvious boiling, transferring it to a freeze dryer, and drying it at -10°C for 8-10 hours to obtain the fertilizer iron supplement additive.

[0030] Furthermore, in step S3, the adsorbent is prepared by the following steps:

[0031] A1. After washing the wood powder with deionized water, dry it in a drying oven at 60℃ for 8 hours to obtain pure wood powder.

[0032] A2. Add pure wood powder to a reaction vessel containing sodium hydroxide solution, stir at 80-90℃ for 2-3 hours, and then perform post-treatment to obtain activated wood powder.

[0033] A3. Place nitroglycerin, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloric acid, N-hydroxythiosuccinimide and deionized water in a reaction vessel, add hydrochloric acid solution dropwise to adjust the pH of the solution to 4.5-5.5, stir at 20-30℃ for 20-30 min, then add activated wood powder, stir at 60-70℃ for 1-2 h, and then perform post-treatment to obtain the adsorbent.

[0034] Reaction principle:

[0035] First, the wood flour is purified by washing and drying with deionized water to remove impurities from its surface. Then, the purified wood flour is activated using a sodium hydroxide solution. This strong alkali removes some lignin from the wood flour, promotes the swelling of the cellulose structure, and disrupts the original dense morphology of the wood flour to increase its specific surface area. Simultaneously, it activates the hydroxyl groups of the cellulose on the wood flour surface, enhancing its reactivity. Finally, the pH of the system is adjusted with hydrochloric acid to suit the activation properties of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloric acid. The carbodiimide hydrochloride (CDI) first reacts with the carboxyl group of triacetic acid to form an unstable O-acylisourea intermediate. N-hydroxythiosuccinimide then combines with this intermediate to form a stable N-hydroxythiosuccinimide activated ester. Subsequently, activated wood flour is added, and under heating conditions, the activated hydroxyl groups on its surface undergo a nucleophilic substitution reaction with the N-hydroxythiosuccinimide activated ester of triacetic acid, grafting triacetic acid molecules onto the surface of the wood flour through ester bonds. After washing and drying, the final product is an adsorbent with surface-grafted triacetic acid.

[0036] Further, in step A2, the ratio of the pure wood powder to the sodium hydroxide solution is 3g:100mL, and the mass fraction of the sodium hydroxide solution is 10%. The post-treatment operation includes: after the reaction, repeatedly washing with deionized water until the washing liquid is neutral, filtering, placing it in a drying oven, and drying at 60℃ to constant weight to obtain activated wood powder; in step A3, the ratio of the aminotriacetic acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloric acid, N-hydroxythiosuccinimide, deionized water, and activated wood powder is 0.2-0.3g:0.5-0.6g:0.1-0.2g:200mL:1g, and the mass fraction of the hydrochloric acid solution is 5%. The post-treatment operation includes: after the reaction, letting it stand for 10-20min, then washing with deionized water 3-5 times, filtering, transferring it to a drying oven, and drying at 60℃ for 8h to obtain the adsorbent.

[0037] The present invention has the following beneficial effects:

[0038] 1. In this invention, firstly, the roasting process under an air atmosphere can destroy the crystal structure of LiFePO4 in the iron phosphate slag, converting it into Li3Fe2(PO4)3·2Fe2O3, which readily reacts with sulfuric acid. Subsequently, leaching with sulfuric acid solution effectively separates soluble lithium salts and insoluble iron components, laying the foundation for subsequent iron enrichment. Then, using a mixed system of hydrogen peroxide and sulfuric acid, with hydrogen peroxide as the oxidant, the iron phosphate and iron oxide in the purified iron slag can be efficiently converted into soluble iron ions, avoiding the loss of iron as insoluble residues. Finally, a self-made adsorbent, activated with wood powder and grafted with nitric acid, can accurately adsorb phosphate ions in the iron ion leachate under a weakly acidic environment, while retaining iron ions, thus solving the interference of phosphate ions on iron recovery. Subsequently, elemental iron is added to further enhance the iron recovery process. 3+ Reduced to Fe 2+ This further reduces iron loss during the separation process. The entire process works closely together to create a synergistic effect, effectively reducing iron loss at each stage and ultimately achieving efficient iron recovery.

[0039] 2. In this invention, on the one hand, the high recovery rate process described above provides a sufficient high-purity iron source for fertilizer preparation. Steps S1-S3, through calcination purification, efficient leaching, and precise impurity removal, ensure that the impurity content in the iron ion leachate is extremely low, avoiding competition between impurities and iron ions for subsequent complexation sites. On the other hand, the specific phosphorus removal effect of the adsorbent in step S3 is crucial. It can completely remove phosphate ions from the solution, preventing phosphate ions from combining with iron ions to form insoluble iron phosphate precipitates, ensuring that iron ions exist in the ferrous solution in a high-purity state. At the same time, in step S2, by controlling the ratio of hydrogen peroxide to sulfuric acid and the reaction temperature, the iron components can be fully dissolved into iron ions, reducing the generation of undissolved iron slag. The synergistic effect of these processes significantly improves the effective iron ion concentration and purity in the ferrous solution. When complexing with fulvic acid solution in step S4, iron ions can fully combine with the carboxyl and phenolic hydroxyl groups of fulvic acid to form a stable ferrous fulvic acid complex, with no impurities hindering the complexation reaction, ultimately greatly increasing the iron content in the fertilizer additive.

[0040] 3. In this invention, firstly, the iron in the fertilizer exists in the form of ferrous fulvic acid complex. This structure not only maintains stability in the soil, preventing it from being fixed as ineffective iron by calcium ions, aluminum ions, etc. in the soil, but also allows for efficient absorption by tomato roots, solving problems such as leaf yellowing and decreased photosynthetic efficiency caused by iron deficiency in tomatoes. Secondly, the precise impurity removal throughout the process ensures that there are no excess impurity ions in the fertilizer, which will not damage the soil environment or stress the tomato roots. On the contrary, fulvic acid itself can stimulate tomato root growth, increase root surface area and root length, and enhance the tomato's ability to absorb water and other nutrients. In addition, the synergistic effect of high available iron content and fulvic acid can promote the physiological metabolic process of tomatoes, increase the fruit enlargement rate and fruit set rate, and reduce fruit drop caused by iron deficiency. The synergistic advantages from the process to the product performance ultimately make this fertilizer show a significant yield-increasing effect in tomato cultivation. Detailed Implementation

[0041] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] In this application, the wood flour is selected from Lingshou County Ningbo Mineral Products Co., Ltd., contains 0.17% impurities, and has the product number mf20240327.

[0043] Example 1

[0044] This embodiment provides a method for preparing iron-supplementing fertilizer additives by recycling ferric phosphate slag, including the following steps:

[0045] Weigh 100g of ferric phosphate slag and place it in a tube furnace. Roast it in air at 600℃ for 2 hours, then immerse it in 400mL of 10wt% sulfuric acid solution and leach it at 40℃ for 30 minutes. Filter the solution to obtain purified slag.

[0046] S2. Preparation of iron ion leachate

[0047] Weigh 100g of purified iron slag and add it to a reaction vessel containing 35mL of hydrogen peroxide and 400mL of 25wt% sulfuric acid solution. Stir at 50℃ for 1h to obtain iron ion leachate.

[0048] S3. Preparation of Adsorbent

[0049] Weigh out 100g of wood flour, wash it with deionized water, and dry it in a drying oven at 60℃ for 8 hours to obtain pure wood flour.

[0050] Weigh 30g of pure wood powder and add it to a reaction vessel containing 1000mL of 10wt% sodium hydroxide solution. Stir at 80℃ for 2h. After the reaction is complete, wash repeatedly with deionized water until the washing liquid is neutral. Filter and put it into a drying oven to dry at 60℃ to constant weight to obtain activated wood powder.

[0051] Weigh out 2g of nitric acid, 5g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloric acid, 1g of N-hydroxythiosuccinimide, and 2000mL of deionized water and place them in a reaction vessel. Add 5wt% hydrochloric acid solution dropwise to adjust the pH of the solution to 4.5. Stir at 20℃ for 20min, then add 10g of activated wood powder and stir at 60℃ for 1h. After the reaction is complete, let it stand for 10min, then wash it three times with deionized water, filter it, transfer it to a drying oven, and dry it at 60℃ for 8h to obtain the adsorbent.

[0052] S4. Preparation of ferrous solution

[0053] Weigh 10g of adsorbent and add it to 1L of iron ion leaching solution. Adsorb at 20℃ for 1h, filter, add 4g of elemental iron to the filtrate, stir at 50℃ for 40min, filter, and obtain ferrous solution.

[0054] S5. Preparation of iron-supplementing fertilizer additives

[0055] Weigh: Add 100 mL of ferrous solution to 200 mL of 2.25 wt% fulvic acid solution, stir at 20 °C for 20 min, after the reaction is complete, transfer to a rotary flask, concentrate by rotary evaporation at 40 °C until no obvious boiling occurs, transfer to a freeze dryer, and dry at -10 °C for 8 h to obtain the fertilizer iron supplement additive.

[0056] Example 2

[0057] This embodiment provides a method for preparing iron-supplementing fertilizer additives by recycling ferric phosphate slag, including the following steps:

[0058] S1. Preparation of purified iron slag

[0059] Weigh 100g of ferric phosphate slag and place it in a tube furnace. Roast it in air at 600℃ for 2.5h, then immerse it in 500mL of 10wt% sulfuric acid solution and leach it at 50℃ for 40min. Filter the solution to obtain purified slag.

[0060] S2. Preparation of iron ion leachate

[0061] Weigh 100g of purified iron slag and add it to a reaction vessel containing 40mL of hydrogen peroxide and 450mL of 25wt% sulfuric acid solution. Stir at 60℃ for 1.5h to obtain iron ion leachate.

[0062] S3. Preparation of Adsorbent

[0063] Weigh out 100g of wood flour, wash it with deionized water, and dry it in a drying oven at 60℃ for 8 hours to obtain pure wood flour.

[0064] Weigh 30g of pure wood powder and add it to a reaction vessel containing 1000mL of 10wt% sodium hydroxide solution. Stir at 85℃ for 2.5h. After the reaction is complete, wash repeatedly with deionized water until the washing liquid is neutral. Filter and place it in a drying oven to dry at 60℃ to constant weight to obtain activated wood powder.

[0065] Weigh out 2.5g of nitric acid, 5.5g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloric acid, 1.5g of N-hydroxythiosuccinimide, and 2000mL of deionized water and place them in a reaction vessel. Add 5wt% hydrochloric acid solution dropwise to adjust the pH of the solution to 5.0. Stir at 25℃ for 25min. Then add 10g of activated wood powder and stir at 65℃ for 1.5h. After the reaction is complete, let it stand for 15min, then wash it 4 times with deionized water, filter it, transfer it to a drying oven, and dry it at 60℃ for 8h to obtain the adsorbent.

[0066] S4. Preparation of ferrous solution

[0067] Weigh 15g of adsorbent and add it to 1L of iron ion leaching solution. Adsorb at 25℃ for 1.5h, filter, add 6g of elemental iron to the filtrate, stir at 55℃ for 45min, filter, and obtain ferrous solution.

[0068] S5. Preparation of iron-supplementing fertilizer additives

[0069] Weigh: Add 100 mL of ferrous solution to 250 mL of 2.25 wt% fulvic acid solution, stir at 25 °C for 25 min, after the reaction is complete, transfer to a rotary flask, concentrate by rotary evaporation at 40 °C until no obvious boiling occurs, transfer to a freeze dryer, and dry at -10 °C for 9 h to obtain the fertilizer iron supplement additive.

[0070] Example 3

[0071] This embodiment provides a method for preparing iron-supplementing fertilizer additives by recycling ferric phosphate slag, including the following steps:

[0072] S1. Preparation of purified iron slag

[0073] Weigh 100g of ferric phosphate slag and place it in a tube furnace. Roast it in air at 700℃ for 3 hours, then immerse it in 600mL of 10wt% sulfuric acid solution and leach it at 60℃ for 50 minutes. Filter the solution to obtain purified slag.

[0074] S2. Preparation of iron ion leachate

[0075] Weigh 100g of purified iron slag and add it to a reaction vessel containing 45mL of hydrogen peroxide and 500mL of 25wt% sulfuric acid solution. Stir at 70℃ for 2 hours to obtain iron ion leachate.

[0076] S3. Preparation of Adsorbent

[0077] Weigh out 100g of wood flour, wash it with deionized water, and dry it in a drying oven at 60℃ for 8 hours to obtain pure wood flour.

[0078] Weigh 30g of pure wood powder and add it to a reaction vessel containing 1000mL of 10wt% sodium hydroxide solution. Stir at 90℃ for 3h. After the reaction is complete, wash repeatedly with deionized water until the washing liquid is neutral. Filter and put it into a drying oven to dry at 60℃ to constant weight to obtain activated wood powder.

[0079] Weigh out 3g of aminotriacetic acid, 6g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloric acid, 2g of N-hydroxythiosuccinimide, and 2000mL of deionized water and place them in a reaction vessel. Add 5wt% hydrochloric acid solution dropwise to adjust the pH of the solution to 5.5. Stir at 30℃ for 30min, then add 10g of activated wood powder and stir at 70℃ for 2h. After the reaction is complete, let it stand for 20min, then wash it 5 times with deionized water, filter, transfer it to a drying oven, and dry it at 60℃ for 8h to obtain the adsorbent.

[0080] S4. Preparation of ferrous solution

[0081] Weigh 20g of adsorbent and add it to 1L of ferric ion leaching solution. Adsorb at 30℃ for 2h, filter, add 8g of elemental iron to the filtrate, stir at 60℃ for 50min, filter, and obtain ferrous solution.

[0082] S5. Preparation of iron-supplementing fertilizer additives

[0083] Weigh out: Add 100 mL of ferrous solution to 300 mL of 2.25 wt% fulvic acid solution, stir at 30 °C for 30 min, after the reaction is complete, transfer to a rotary flask, concentrate by rotary evaporation at 40 °C until no obvious boiling occurs, transfer to a freeze dryer, and dry at -10 °C for 10 h to obtain the fertilizer iron supplement additive.

[0084] Comparative Example 1

[0085] The difference between this comparative example and Example 3 is that step S1 is omitted, and the ferric phosphate residue is directly added to a solution of hydrogen peroxide and sulfuric acid for leaching.

[0086] Comparative Example 2

[0087] The difference between this comparative example and Example 3 is that step S3 is omitted and no adsorbent is added in step S4.

[0088] Comparative Example 3

[0089] The difference between this comparative example and Example 3 is that step S5 is omitted, and the ferrous solution prepared in step S4 is directly used as an iron supplement additive.

[0090] Performance testing:

[0091] The iron recovery rate in the fertilizer iron supplement additives prepared in Examples 1-3 and Comparative Examples 1-3 was determined according to the standard T / SPSTS 003-2018 "Recycling of Waste Lithium Iron Phosphate Batteries by Wet Process".

[0092] The iron content in the iron-supplementing fertilizers prepared in Examples 1-3 and Comparative Examples 1-3 was determined according to the standard GB / T 34764-2017 "Determination of Copper, Iron, Manganese, Zinc, Boron and Molybdenum Content in Fertilizers - Plasma Atomic Emission Spectrometry".

[0093] A pot experiment was conducted using pots with a diameter and depth of 40 cm. The soil was air-dried, crushed, and sieved. Each pot contained 10 kg of dry soil. Iron supplement was mixed thoroughly with the dry soil, then placed in the pots and allowed to settle for one week. The experiment included six treatment combinations, with a control group receiving no iron supplement. In each treatment, the iron supplement dosage was the same: 100 kg / hm². 2 Each treatment was repeated three times, with a total of 20 potted plants used to determine tomato growth dynamics and yield. Specific test results are shown in Table 1 below:

[0094] Table 1 - Basic Performance Test Data of the Samples

[0095]

[0096] Data Analysis:

[0097] Comparative analysis of the data in Table 1 above shows that the present invention provides a method for preparing iron-supplementing fertilizer by recovering ferric phosphate slag. During the preparation process, the iron recovery rate is 99.5%, and the iron content in the prepared iron-supplementing fertilizer is 18.8%. After experiments with tomatoes, the yield of tomatoes was increased.

[0098] The iron recovery rate, iron content, and tomato yield of Comparative Examples 1-3 were all much lower than those of the Example. The main reason is that Comparative Example 1 omitted the roasting treatment in step S1, so the lattice of LiFePO4 in the iron phosphate slag was not destroyed. Its high chemical stability prevented it from fully reacting with the subsequent hydrogen peroxide-sulfuric acid mixed solution, resulting in incomplete leaching of iron components. A large amount of iron remained in the form of undissolved slag, so the iron recovery rate was only 80.6%. At the same time, impurities in the unroasted slag directly entered the leachate, competing with iron ions for complexation sites of fulvic acid, reducing the complexation efficiency between iron and fulvic acid, so the iron content was only 15.4%. The fertilizer had insufficient available iron and many impurities, which not only failed to solve the iron deficiency problem of tomatoes, but also caused slight stress to the tomato roots, resulting in low photosynthetic efficiency and fewer fruits, so the yield was only 2.11 kg.

[0099] In Comparative Example 2, because the adsorbent addition in step S3 was omitted, phosphate ions in the iron ion leachate could not be specifically removed and would combine with iron ions to form insoluble iron phosphate precipitate, resulting in a large loss of iron ions. Therefore, the iron recovery rate dropped to 85.4%. Furthermore, the precipitation would reduce the concentration of effective iron ions in the ferrous solution, reducing the number of iron ions that could participate in the reaction when complexing with fulvic acid, thus reducing the iron content to 16.2%. Due to the insufficient effective iron content in the fertilizer, the iron deficiency and yellowing problem of tomatoes was not effectively alleviated, and the accumulation of photosynthetic products was low, resulting in a yield of only 2.19 kg.

[0100] Comparative Example 3 omitted the fulvic acid complexation step in step S4 and directly used ferrous solution as an iron supplement. Ferrous ions are easily fixed in the soil by calcium ions, aluminum ions, etc., into ineffective Fe(OH)2 or Fe2O3, which tomatoes cannot absorb efficiently. Therefore, even though the iron recovery rate and iron content are close to those of the example, the actual amount of effective iron that tomatoes can utilize is still very small. In addition, the lack of fulvic acid to stimulate the root system restricts the growth of tomato roots and weakens the nutrient absorption capacity, resulting in a yield of only 2.25 kg.

[0101] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for recovering ferric phosphate slag to prepare iron-supplementing fertilizer additives, characterized in that, Includes the following steps: S1. Place the ferric phosphate slag in a tube furnace and roast it in an air atmosphere at 600-700℃ for 2-3 hours. Then, immerse it in a sulfuric acid solution and leach it at 40-60℃ for 30-50 minutes. Filter the solution to obtain purified slag. S2. Add the purified iron slag to a reaction vessel containing hydrogen peroxide and sulfuric acid solution, and stir at 50-70℃ for 1-2 hours to obtain an iron ion leachate. S3. Add adsorbent to the iron ion leaching solution, adsorb at 20-30℃ for 1-2 hours, filter, add elemental iron to the filtrate, stir at 50-60℃ for 40-50 minutes, filter, and obtain ferrous solution. S4. Add the ferrous solution to the fulvic acid solution and stir at 20-30℃ for 20-30 minutes. After post-treatment, the fertilizer iron supplement additive is obtained.

2. The method for preparing iron-supplementing fertilizer additives by recovering ferric phosphate slag according to claim 1, characterized in that, In step S1, the ratio of the amount of ferric phosphate residue to sulfuric acid solution is 1g:4-6mL, and the mass fraction of the sulfuric acid solution is 10%.

3. The method for preparing iron-supplementing fertilizer additives by recovering ferric phosphate slag according to claim 2, characterized in that, In step S2, the ratio of the amount of purified iron slag, hydrogen peroxide and sulfuric acid solution is 100g:35-45mL:400-500mL, and the mass fraction of the sulfuric acid solution is 25%.

4. The method for preparing iron-supplementing fertilizer additives by recovering ferric phosphate slag according to claim 1, characterized in that, In step S3, the ratio of the amount of iron ion leachate, adsorbent and elemental iron is 1L:10-20g:4-8g.

5. The method for preparing iron-supplementing fertilizer additives by recovering ferric phosphate slag according to claim 1, characterized in that, In step S4, the ratio of ferrous solution to fulvic acid solution is 1 mL: 2-3 mL, and the mass fraction of fulvic acid solution is 2.25%. The post-processing operation includes: after the reaction is completed, transferring the solution to a rotary flask and concentrating it at 40°C until there is no obvious boiling, then transferring it to a freeze dryer and drying it at -10°C for 8-10 hours to obtain the fertilizer iron supplement additive.

6. The method for preparing iron-supplementing fertilizer additives by recovering ferric phosphate slag according to claim 1, characterized in that, In step S3, the adsorbent is prepared by the following steps: A1. After washing the wood powder with deionized water, dry it in a drying oven at 60℃ for 8 hours to obtain pure wood powder. A2. Add pure wood powder to a reaction vessel containing sodium hydroxide solution, stir at 80-90℃ for 2-3 hours, and then perform post-treatment to obtain activated wood powder. A3. Place nitroglycerin, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloric acid, N-hydroxythiosuccinimide and deionized water in a reaction vessel, add hydrochloric acid solution dropwise to adjust the pH of the solution to 4.5-5.5, stir at 20-30℃ for 20-30 min, then add activated wood powder, stir at 60-70℃ for 1-2 h, and then perform post-treatment to obtain the adsorbent.

7. The method for preparing iron-supplementing fertilizer additives by recovering ferric phosphate slag according to claim 6, characterized in that, In step A2, the ratio of pure wood powder to sodium hydroxide solution is 3g:100mL, and the mass fraction of sodium hydroxide solution is 10%. The post-treatment operation includes: after the reaction, repeatedly washing with deionized water until the washing liquid is neutral, filtering, placing it in a drying oven, and drying at 60℃ to constant weight to obtain activated wood powder. In step A3, the ratio of aminotriacetic acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloric acid, N-hydroxythiosuccinimide, deionized water, and activated wood powder is 0.2-0.3g:0.5-0.6g:0.1-0.2g:200mL:1g, and the mass fraction of hydrochloric acid solution is 5%. The post-treatment operation includes: after the reaction, letting it stand for 10-20min, then washing with deionized water 3-5 times, filtering, transferring it to a drying oven, and drying at 60℃ for 8h to obtain the adsorbent.

Images