A method for synergistically synthesizing iron phosphate by using phosphorus-containing waste salt and iron-containing waste acid

Abstract

The present application relates to a kind of method for synthesizing iron phosphate by phosphorus-containing waste salt and iron-containing waste acid, the synthesis method includes, phosphorus-containing waste salt is dissolved, hydrolysis, filtration, obtain filtrate, first oxidizing agent is added in filtrate and is oxidized, subsequently modified mesoporous activated carbon is added and is adsorbed, and phosphorus salt purification liquid is obtained by separation;Iron is added in iron-containing waste acid and is reduced, and the pH value is adjusted to precipitate impurities, subsequently chitosan-sodium alginate composite flocculant is added, and ferrous purification liquid is obtained by separation after flocculation;Phosphorus salt purification liquid, ferrous purification liquid, second oxidizing agent are mixed, and after oxidation reaction, insoluble is collected, and iron phosphate is obtained by processing.The modified mesoporous activated carbon and composite flocculant of the present application can efficiently remove organic matter and heavy metal in the system, reduce the accumulation of impurities in the system, improve the purity of the final product, realize the morphology controllable of iron phosphate product, particle size is uniform, and the obtained iron phosphate product meets the battery grade iron phosphate standard.

Description

Technical Field

[0001] This invention relates to the field of ferric phosphate technology, specifically to a method for synergistic synthesis of ferric phosphate using phosphorus-containing waste salt and iron-containing waste acid. Background Technology

[0002] Iron phosphate (FePO4) is a key precursor for the preparation of lithium iron phosphate (LiFePO4), a cathode material for lithium-ion batteries. With the rapid development of new energy vehicles and energy storage industries, its market demand continues to grow. Currently, the industrial production of iron phosphate mainly involves the synthesis of ferrous sulfate and phosphates (such as monoammonium phosphate and diammonium dihydrogen phosphate) under the action of an oxidant. However, this process requires high purity raw materials, necessitating the use of refined phosphorus and iron sources, resulting in high production costs and the generation of large amounts of saline wastewater.

[0003] Meanwhile, the industrial sector generates large quantities of phosphorus-containing waste salts and iron-containing waste acids, which urgently need resource utilization. For example, glyphosate production generates a large amount of by-product waste salts containing organophosphorus compounds; steel pickling processes generate iron-containing hydrochloric acid / sulfuric acid waste liquids; and the phosphate chemical industry also generates various types of phosphorus-containing waste salts. Traditional treatment methods for these wastes (such as neutralization precipitation and landfill) are not only costly but also cause resource waste and environmental risks. Some studies have successfully prepared iron phosphate from waste materials. For example, CN115959643A discloses a resource utilization method for by-product phosphate salts and iron salts from steel pickling. An oxidant is added to the filtrate obtained from the hydrolysis of glyphosate by-product phosphate salts for oxidation, followed by adsorption with an adsorbent and filtration to obtain a purified phosphate salt solution. Iron is added to dissolve the iron salts from steel pickling to reduce Fe. 3+ The ferrous sulfate purified solution is obtained by adding flocculant and impurity metal ions and filtering. The resulting phosphate purified solution and ferrous sulfate purified solution are then mixed and an oxidant is added to synthesize ferric phosphate. This method achieves the preparation of ferric phosphate from phosphorus-containing waste salt and iron-containing waste salt, but its treatment steps use commonly used activated carbon adsorption and do not control the particle size of the ferric phosphate product. Summary of the Invention

[0004] The purpose of this invention is to introduce specific modified materials into the purification treatment of phosphorus-containing waste salt and iron-containing waste acid to overcome the problems of unstable product purity, uneven particle size distribution and insufficient treatment efficiency in the prior art, thereby significantly improving the quality of the final product and the stability of the production process.

[0005] To achieve the above-mentioned technical objectives, this invention provides a method for the synergistic synthesis of iron phosphate using phosphorus-containing waste salt and iron-containing waste acid, comprising: The phosphorus-containing waste salt is dissolved, hydrolyzed, and filtered to obtain a filtrate. A first oxidant is added to the filtrate to carry out an oxidation reaction, followed by the addition of modified activated carbon for adsorption, and the phosphorus salt purified solution is obtained by separation. Iron was added to the iron-containing waste acid to carry out a reduction reaction, the pH value was adjusted to precipitate impurities, and then chitosan-sodium alginate composite flocculant was added. After flocculation, the ferrous purified liquid was obtained by separation. The phosphate purification solution, ferrous purification solution, and second oxidant are mixed, and after oxidation, the insoluble matter is collected and processed to obtain ferric phosphate.

[0006] Furthermore, the method for preparing the modified activated carbon includes, Activated carbon is heat-treated in a protective gas atmosphere at a first temperature to obtain pretreated activated carbon. Pretreated activated carbon was treated in a mixed solution of urea and citric acid, and then the insoluble matter was collected and heat-treated under a protective atmosphere at a second temperature to obtain modified activated carbon.

[0007] Furthermore, the first temperature and the second temperature are 800-900℃ and 500-600℃, respectively; The mass concentrations of urea and citric acid in the mixed solution are both 5%-10%. The treatment time in the mixed solution is 8-15 hours.

[0008] Furthermore, the preparation method of the chitosan-sodium alginate composite flocculant includes, Chitosan acid solution and sodium alginate solution, both with a mass concentration of 0.5%-2%, are mixed at a volume ratio of 1-2:1-2 and stirred at a temperature of 40-60℃ to obtain a chitosan-sodium alginate composite flocculant.

[0009] Furthermore, the dissolution and hydrolysis of the phosphorus-containing waste salt are carried out at a temperature of 25-35℃ and a pH of 3-5; The amount of the first oxidant added is 0.01%-3% of the mass of the phosphorus-containing waste salt; The amount of modified activated carbon added is 0.01%-0.1% of the mass of the filtrate.

[0010] Furthermore, the amount of iron added is 1%-2% of the mass of iron in the iron-containing waste acid; The precipitation of impurities was carried out at a pH of 4.0-5.5; The chitosan-sodium alginate composite flocculant is added at a dosage of 0.05-0.1 g / L.

[0011] Furthermore, the phosphate purification solution and the ferrous purification solution are mixed at a P to Fe molar ratio of 0.95-1.05:1; The amount of the second oxidant added is 1.0-1.5 times the theoretical oxygen demand; The oxidation reaction is carried out at a pH of 1.5-3.5 and a temperature of 40-80℃ for 2-6 hours.

[0012] Furthermore, the process to obtain ferric phosphate includes washing, drying, and heat treatment, wherein the heat treatment is carried out at 500-700℃ for 2-6 hours.

[0013] Furthermore, when mixing the phosphate purification solution, the ferrous purification solution, and the second oxidant, 0.05%-0.2% by weight of the ferrous purification solution of polyethylene glycol is added, wherein the molecular weight of the polyethylene glycol is 1000-4000. The phosphate purification solution, ferrous purification solution, and second oxidant are mixed in a parallel flow ratio of 0.9-1.1:0.8-1.0:0.1-0.2, with a total feeding time of 1-2 hours. After collecting the insoluble matter, the separated reaction mother liquor is further purified to recover salt and reuse the solvent.

[0014] The present invention also provides an iron phosphate, which is obtained by the above-described method of synergistic synthesis of iron phosphate using phosphorus-containing waste salt and iron-containing waste acid.

[0015] Compared with the prior art, the beneficial effects of the present invention include: (1) Using phosphorus-containing waste salt as phosphorus source and iron-containing waste acid as iron source, the two types of waste are applied to the preparation of high-value-added iron phosphate materials, realizing the purpose of turning waste into treasure and reducing the production cost of iron phosphate.

[0016] (2) The use of modified activated carbon and composite flocculant can efficiently remove organic matter and heavy metals in the system, reduce the accumulation of impurities in the system, and improve the purity of the final product.

[0017] (3) The morphology of the iron phosphate product is controllable and the particle size is uniform. The resulting iron phosphate product meets the battery-grade iron phosphate standard.

[0018] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0020] Figure 1 The XRD pattern of the iron phosphate prepared in Example 1 is shown; Figure 2A scanning electron microscope image of the iron phosphate prepared in Example 1 is shown; Figure 3 A scanning electron microscope image of the iron phosphate prepared in Comparative Example 1 is shown; Figure 4 A scanning electron microscope image of the iron phosphate prepared in Comparative Example 2 is shown; Figure 5 A scanning electron microscope image of the iron phosphate prepared in Comparative Example 3 is shown. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0023] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0024] The design concept of this invention is to introduce specific modified materials into the purification treatment of phosphorus-containing waste salt and iron-containing waste acid, which can efficiently remove organic matter and heavy metals from the system, reduce the accumulation of impurities in the system, and overcome the problems of unstable product purity, uneven particle size distribution, and the need to improve treatment efficiency.

[0025] Accordingly, the present invention provides a method for synergistic synthesis of iron phosphate using phosphorus-containing waste salt and iron-containing waste acid, comprising, The phosphorus-containing waste salt is dissolved, hydrolyzed, and filtered to obtain a filtrate. A first oxidant is added to the filtrate to carry out an oxidation reaction, followed by the addition of modified activated carbon for adsorption, and the phosphorus salt purified solution is obtained by separation. Iron was added to the iron-containing waste acid to carry out a reduction reaction, the pH value was adjusted to precipitate impurities, and then chitosan-sodium alginate composite flocculant was added. After flocculation, the ferrous purified liquid was obtained by separation. The phosphate purification solution, ferrous purification solution, and second oxidant are mixed, and after oxidation, the insoluble matter is collected and processed to obtain ferric phosphate.

[0026] In some preferred embodiments, the method for preparing the modified activated carbon includes, Activated carbon is heat-treated in a protective gas atmosphere at a first temperature to obtain pretreated activated carbon. Pretreated activated carbon was treated in a mixed solution of urea and citric acid, and then the insoluble matter was collected and heat-treated under a protective atmosphere at a second temperature to obtain modified activated carbon.

[0027] In some preferred embodiments, the first temperature and the second temperature are 800-900°C and 500-600°C, respectively; The mass concentrations of urea and citric acid in the mixed solution are both 5%-10%. The treatment time in the mixed solution is 8-15 hours.

[0028] In some preferred embodiments, the preparation method of the chitosan-sodium alginate composite flocculant includes, Chitosan acid solution and sodium alginate solution, both with a mass concentration of 0.5%-2%, are mixed at a volume ratio of 1-2:1-2 and stirred at a temperature of 40-60℃ to obtain a chitosan-sodium alginate composite flocculant.

[0029] In some preferred embodiments, the dissolution and hydrolysis of the phosphorus-containing waste salt are carried out at a temperature of 25-35°C and a pH of 3-5; The amount of the first oxidant added is 0.01%-3% of the mass of the phosphorus-containing waste salt; The amount of modified activated carbon added is 0.01%-0.1% of the mass of the filtrate.

[0030] In some preferred embodiments, the amount of iron added is 1%-2% of the mass of iron in the iron-containing waste acid; The precipitation of impurities was carried out at a pH of 4.0-5.5; The chitosan-sodium alginate composite flocculant is added at a dosage of 0.05-0.1 g / L.

[0031] In some preferred embodiments, the phosphate purification solution and the ferrous purification solution are mixed at a P to Fe molar ratio of 0.95-1.05:1; The amount of the second oxidant added is 1.0-1.5 times the theoretical oxygen demand; The oxidation reaction is carried out at a pH of 1.5-3.5 and a temperature of 40-80℃ for 2-6 hours.

[0032] In some preferred embodiments, when mixing the phosphate purification solution, the ferrous purification solution, and the second oxidant, 0.05%-0.2% by weight of the ferrous purification solution of polyethylene glycol is also added, wherein the molecular weight of the polyethylene glycol is 1000-4000. The phosphate purification solution, ferrous purification solution, and second oxidant are mixed in a parallel flow ratio of 0.9-1.1:0.8-1.0:0.1-0.2, with a total feeding time of 1-2 hours. After collecting the insoluble matter, the separated reaction mother liquor is further purified to recover salt and reuse the solvent.

[0033] It should be noted that the sources of phosphorus-containing waste salt and iron-containing waste acid are not strictly limited in this invention. Exemplarily, the phosphorus-containing waste salt can be at least one of the following: glyphosate production by-product phosphate salts, waste phosphates generated from heavy metal precipitation, etc.; the iron-containing waste acid can be at least one of the following: steel pickling waste liquid, titanium dioxide by-product ferrous sulfate solution, etc. The solvent for dissolving the phosphorus-containing waste salt is not strictly limited; exemplarily, at least one of water, ethanol, acetone, phosphoric acid, sulfuric acid, etc., can be used. The solvent for the mixed solution of urea and citric acid is not strictly limited; exemplarily, at least one of water, ethanol, acetone, etc., can be used. The solvent for the chitosan acid solution and sodium alginate solution is not strictly limited; exemplarily, at least one of water, ethanol, acetone, etc., can be used. The acid in the chitosan acid solution can be provided by acetic acid, hydrochloric acid, etc., and the specific acid concentration is not strictly limited; it can be a low concentration that chitosan can effectively dissolve. The first and second oxidizing agents are not strictly limited and are both commonly used reagents in the art. Exemplarily, they can be at least one of hydrogen peroxide, sodium perchlorate, sodium chlorate, sodium chlorite, sodium hypochlorite, etc. Based on the co-current addition of the second oxidizing agent, the second oxidizing agent is preferably liquid hydrogen peroxide. Of course, a solid oxidizing agent can also be dissolved in water or other solvents, as long as it ensures complete oxidization of ferrous iron. The protective atmosphere can be provided by at least one of nitrogen, helium, argon, etc.

[0034] The present invention will be further described in detail below through specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0035] Example 1 A method for synergistically synthesizing iron phosphate using phosphorus-containing waste salt and iron-containing waste acid includes the following steps: (1) Purification treatment of phosphorus-containing waste salt Take 100 kg of by-product phosphate salt (mainly sodium phosphate salt with a small amount of organic matter) from a glyphosate production enterprise, add 300 L of water and stir to mix. Adjust the pH to 4.0 with dilute sulfuric acid, dissolve at 30℃, maintain the temperature and hydrolyze for 2 hours. Remove insoluble matter by plate and frame filtration, add 2 kg of sodium chlorate to the filtrate and oxidize for 1 hour. Then add 0.05 kg of modified activated carbon and stir for adsorption. After 1.5 hours, filter to obtain purified phosphate salt solution.

[0036] (2) Purification treatment of iron-containing waste acid Take 200L of hydrochloric acid pickling waste liquid (containing Fe) from a cold-rolled steel plant 2+ 65g / L, Fe 3+ Add 3 kg of iron powder (8 g / L, about 3% free HCl), stir and react for 2 hours, adjust the pH to 4.5 with liquid alkali to hydrolyze and precipitate the metal ion impurities, then add 15 g of chitosan-sodium alginate composite flocculant, stir and flocculate, filter, and obtain ferrous purified solution.

[0037] (3) Synthesis of iron phosphate Deionized water was pre-added to the reactor as a base solution, heated to 60°C, and the pH was adjusted to 2.0. Phosphate purification solution (P concentration 18 g / L) and ferrous purification solution (Fe...) were then added... 2+ 70 g / L of ferrous oxide and 27.5% hydrogen peroxide were added to the reactor in parallel flow at a P:Fe molar ratio of 1.02:1 and a hydrogen peroxide concentration of 1.1 times the theoretical oxygen demand, using three metering pumps at a volumetric flow rate ratio of 1:0.9:0.15. The total feeding time was controlled to be 1.5 hours to form the reaction system. Simultaneously, polyethylene glycol (PEG-2000) with a molecular weight of 2000 was added to the reaction system at a concentration of 0.1% of the total mass of the ferrous oxide purification solution. The pH of the system was controlled between 2.0 and 3.0 during the reaction. After the feeding was completed, the reaction was continued at this temperature for 2 hours.

[0038] (4) Post-processing The reaction slurry formed in step (3) is pumped into a plate and frame filter press to obtain ferric phosphate filter cake and reaction mother liquor. The filter cake is washed three times with deionized water, and the wash water and mother liquor are combined and sent to the salt recovery unit. The washed filter cake is dried at 120°C for 4 hours and then calcined at 600°C for 4 hours to obtain anhydrous ferric phosphate product.

[0039] (5) Reuse After combining the washing water and the reaction mother liquor, impurities are removed, and the mixture is evaporated and concentrated to obtain industrial-grade sodium chloride. The condensate is then reused in the washing process.

[0040] The method for preparing modified activated carbon includes treating commercially available activated carbon at 850°C for 3 hours under nitrogen protection to obtain pretreated activated carbon; immersing the pretreated activated carbon in an aqueous solution containing 8wt% urea and 8wt% citric acid for 12 hours; collecting the insoluble matter and treating it at 550°C for 3 hours under nitrogen protection to obtain modified activated carbon.

[0041] The preparation method of chitosan-sodium alginate composite flocculant includes dissolving chitosan in 1% acetic acid to prepare a 1% solution, dissolving sodium alginate in water to prepare a 1% solution, mixing the two solutions at a volume ratio of 1:1, and stirring at 50°C for 1 hour to obtain chitosan-sodium alginate composite flocculant.

[0042] Example 2 Compared with Example 1, the difference is that in step (1), the pH is adjusted to 4.5 and the amount of modified activated carbon added is 0.1 kg.

[0043] Example 3 Compared with Example 1, the difference is that in step (2), the pH is adjusted to 5.5 and the amount of chitosan-sodium alginate composite flocculant added is 20g.

[0044] Example 4 Compared with Example 1, the difference is that in step (3), the amount of PEG-2000 added is 0.2% of the total mass of the ferrous purification solution.

[0045] Example 5 Compared with Example 1, the difference is that in the preparation of modified activated carbon, the pretreated activated carbon is immersed in an aqueous solution containing 5 wt% urea and 5 wt% citric acid for 12 h.

[0046] Example 6 Compared with Example 1, the difference is that in the preparation of modified activated carbon, the pretreated activated carbon is immersed in an aqueous solution containing 10wt% urea and 10wt% citric acid for 12h.

[0047] Comparative Example 1 A method for synergistically synthesizing iron phosphate using phosphorus-containing waste salt and iron-containing waste acid includes the following steps: (1) Purification treatment of phosphorus-containing waste salt Take 100 kg of by-product phosphate salt (same as in Example 1) from a glyphosate production enterprise, add 300 L of water and stir to mix. Adjust the pH to 4.0 with dilute sulfuric acid, dissolve at 30°C, maintain the temperature, and hydrolyze for 2 hours. Remove insoluble matter by plate and frame filtration. Add 2 kg of sodium chlorate to the filtrate and oxidize for 1 hour. Then add 0.05 kg of commercially available activated carbon and stir to adsorb. After 1.5 hours, filter to obtain purified phosphate salt solution.

[0048] (2) Purification treatment of iron-containing waste acid Take 200L of hydrochloric acid pickling waste liquid (containing Fe) from a cold-rolled steel plant 2+ 65g / L, Fe 3+ Add 3 kg of iron powder (8 g / L, about 3% free HCl), stir and react for 2 hours. Adjust the pH to 4.5 with liquid alkali to hydrolyze and precipitate the metal ion impurities. Then add 15 g of polyacrylamide, stir and flocculate, filter, and obtain ferrous purified solution.

[0049] (3) Synthesis of iron phosphate Deionized water was pre-added to the reactor as a base solution, heated to 60°C, and the pH was adjusted to 2.0. Phosphate purification solution (P concentration 18 g / L) and ferrous purification solution (Fe...) were then added... 2+ 70 g / L of ferrous oxide and 27.5% hydrogen peroxide were added to the reactor in parallel flow at a P:Fe molar ratio of 1.02:1 and a hydrogen peroxide concentration of 1.1 times the theoretical oxygen demand, using three metering pumps at a volumetric flow rate ratio of 1:0.9:0.15. The total feeding time was controlled to be 1.5 hours to form the reaction system. Simultaneously, polyethylene glycol (PEG-2000) with a molecular weight of 2000 was added to the reaction system at a concentration of 0.1% of the total mass of the ferrous oxide purification solution. The pH of the system was controlled between 2.0 and 3.0 during the reaction. After the feeding was completed, the reaction was continued at this temperature for 2 hours.

[0050] (4) Post-processing The reaction slurry formed in step (3) is pumped into a plate and frame filter press to obtain ferric phosphate filter cake and reaction mother liquor. The filter cake is washed three times with deionized water, and the wash water and reaction mother liquor are combined and sent to the salt recovery unit. The washed filter cake is dried at 120°C for 4 hours and then calcined at 600°C for 4 hours to obtain anhydrous ferric phosphate product.

[0051] (5) Reuse After combining the washing water and the reaction mother liquor, impurities are removed, and the mixture is evaporated and concentrated to obtain industrial-grade sodium chloride. The condensate is then reused in the washing process.

[0052] Comparative Example 2 A method for synergistically synthesizing iron phosphate using phosphorus-containing waste salt and iron-containing waste acid includes the following steps: (1) Purification treatment of phosphorus-containing waste salt Take 100 kg of by-product phosphate salt (same as in Example 1) from a glyphosate production enterprise, add 300 L of water and stir to mix. Adjust the pH to 4.0 with dilute sulfuric acid, dissolve at 30°C, maintain the temperature, and hydrolyze for 2 hours. Remove insoluble matter by plate and frame filtration. Add 2 kg of sodium chlorate to the filtrate and oxidize for 1 hour. Then add 0.05 kg of commercially available activated carbon and stir to adsorb. After 1.5 hours, filter to obtain purified phosphate salt solution.

[0053] (2) Purification treatment of iron-containing waste acid Take 200L of hydrochloric acid pickling waste liquid (containing Fe) from a cold-rolled steel plant 2+ 65g / L, Fe 3+ Add 3 kg of iron powder (8 g / L, about 3% free HCl), stir and react for 2 hours. Adjust the pH to 4.5 with liquid alkali to hydrolyze and precipitate the metal ion impurities. Then add 15 g of polyacrylamide, stir and flocculate, filter, and obtain ferrous purified solution.

[0054] (3) Synthesis of iron phosphate Deionized water was pre-added to the reactor as a base solution, heated to 60°C, and the pH was adjusted to 2.0. Phosphate purification solution (P concentration 18 g / L) and ferrous purification solution (Fe...) were then added... 2+ 70 g / L of ferrous oxide and 27.5% hydrogen peroxide were added to the reactor at a P:Fe molar ratio of 1.02:1, with the hydrogen peroxide concentration being 1.1 times the theoretical oxygen requirement, to form the reaction system. Simultaneously, polyethylene glycol (PEG-2000) with a molecular weight of 2000 was added to the reaction system at a concentration of 0.1% of the total mass of the ferrous oxide purification solution. During the reaction, the pH of the system was controlled between 2.0 and 3.0, and the reaction was maintained at this temperature for 2 hours.

[0055] (4) Post-processing The reaction slurry formed in step (3) is pumped into a plate and frame filter press to obtain ferric phosphate filter cake and reaction mother liquor. The filter cake is washed three times with deionized water, and the wash water and reaction mother liquor are combined and sent to the salt recovery unit. The washed filter cake is dried at 120°C for 4 hours and then calcined at 600°C for 4 hours to obtain anhydrous ferric phosphate product.

[0056] (5) Reuse After combining the washing water and the reaction mother liquor, impurities are removed, and the mixture is evaporated and concentrated to obtain industrial-grade sodium chloride. The condensate is then reused in the washing process.

[0057] Comparative Example 3 The difference from Example 1 is that PEG-2000 is not added to the reaction system in step (3).

[0058] Comparative Example 4 Compared with Example 1, the difference is that in the preparation of modified mesoporous activated carbon, the pretreated activated carbon is immersed in an aqueous solution containing 2wt% urea and 2wt% citric acid for 12h.

[0059] Comparative Example 5 Compared with Example 1, the difference is that in the preparation of modified mesoporous activated carbon, the pretreated activated carbon is immersed in an aqueous solution containing 15wt% urea and 15wt% citric acid for 12h.

[0060] Test case The crystal structure of the iron phosphate materials obtained in Example 1 and Comparative Examples 1-3 was observed using XRD. Figure 1 As can be seen, they are all pure-phase anhydrous ferric phosphate, with no impurity peaks present.

[0061] The microstructure of the iron phosphate materials obtained in Example 1 and Comparative Examples 1-3 was observed using scanning electron microscopy. Figure 2 As can be seen, the iron phosphate in Example 1 exhibits a coral-like structure. Figures 3-5 The results showed that the iron phosphate particles in Comparative Examples 1-3 exhibited severe stacking and agglomeration, resulting in decreased grain regularity. Scanning electron microscopy results indicated that Example 1, through the synergistic effect of modified activated carbon providing uniform nucleation sites, stepwise feeding for stable crystal control, and PEG exerting steric hindrance dispersion, successfully prepared uniformly dispersed coral-like iron phosphate. In contrast, the comparative examples lacking any single condition all showed grain agglomeration and pore collapse, resulting in significantly deteriorated microstructure.

[0062] The iron-to-phosphorus ratio, purity, D50 particle size, and particle size distribution spacing [(D90-D10) / D50] of the iron phosphate materials obtained in Example 1 and Comparative Examples 1-3 were tested, and the test results are shown in Table 1.

[0063] The impurity content of the iron phosphate materials obtained in Examples 1-6 and Comparative Examples 1-5 was tested by ICP, and the test results are shown in Table 2.

[0064] Table 1

[0065] As shown in Table 1, Example 1 exhibits the highest iron-to-phosphorus ratio, purity, smallest D50 particle size, and most concentrated particle size distribution. Furthermore, as shown in Table 2, the impurity content of Examples 1-6 is closer to that of commercially available lithium phosphate, with some impurities showing a significant reduction. This is attributed to the introduction of specific modified materials in the purification treatment of phosphorus-containing waste salt and iron-containing waste acid, which efficiently removes organic matter and heavy metals from the system, reducing impurity accumulation and overcoming the problems of unstable product purity and uneven particle size distribution. In contrast, Comparative Example 1 uses conventional purification materials, which struggle to completely remove organic matter and heavy metals, reducing product purity and affecting particle size distribution. Comparative Example 2 uses a one-time feeding method, resulting in a vigorous reaction process and significant localized peroxidation in the product, leading to severe particle agglomeration and a significant increase in particle size. This also demonstrates the crucial role of co-current feeding and the synergistic effect of the regulator in controlling crystal growth. Compared to Example 1, Comparative Example 3 does not add polyethylene glycol to the reaction system, resulting in a lack of directional control over crystal growth, leading to uncontrolled particle agglomeration and abnormal growth. This also demonstrates that, based on the reaction system of this invention, the addition of polyethylene glycol is crucial for obtaining ferric phosphate products with uniform particle size and regular morphology.

[0066] Table 2

[0067] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for synergistically synthesizing iron phosphate using phosphorus-containing waste salt and iron-containing waste acid, characterized in that, include, The phosphorus-containing waste salt is dissolved, hydrolyzed, and filtered to obtain a filtrate. A first oxidant is added to the filtrate to carry out an oxidation reaction, followed by the addition of modified activated carbon for adsorption, and the phosphorus salt purified solution is obtained by separation. Iron was added to the iron-containing waste acid to carry out a reduction reaction, the pH value was adjusted to precipitate impurities, and then chitosan-sodium alginate composite flocculant was added. After flocculation, the ferrous purified liquid was obtained by separation. The phosphate purification solution, ferrous purification solution, and second oxidant are mixed, and after oxidation, the insoluble matter is collected and processed to obtain ferric phosphate.

2. The method for synergistic synthesis of ferric phosphate using phosphorus-containing waste salt and iron-containing waste acid according to claim 1, characterized in that, The method for preparing the modified activated carbon includes, Activated carbon is heat-treated in a protective gas atmosphere at a first temperature to obtain pretreated activated carbon. Pretreated activated carbon was treated in a mixed solution of urea and citric acid, and then the insoluble matter was collected and heat-treated under a protective atmosphere at a second temperature to obtain modified activated carbon.

3. The method for synergistic synthesis of ferric phosphate using phosphorus-containing waste salt and iron-containing waste acid according to claim 2, characterized in that, The first temperature and the second temperature are 800-900℃ and 500-600℃, respectively; The mass concentrations of urea and citric acid in the mixed solution are both 5%-10%. The treatment time in the mixed solution is 8-15 hours.

4. The method for synergistic synthesis of ferric phosphate using phosphorus-containing waste salt and iron-containing waste acid according to claim 1, characterized in that, The preparation method of the chitosan-sodium alginate composite flocculant includes, Chitosan acid solution and sodium alginate solution, both with a mass concentration of 0.5%-2%, are mixed at a volume ratio of 1-2:1-2 and stirred at a temperature of 40-60℃ to obtain a chitosan-sodium alginate composite flocculant.

5. The method for synergistic synthesis of ferric phosphate using phosphorus-containing waste salt and iron-containing waste acid according to claim 1, characterized in that, The dissolution and hydrolysis of the phosphorus-containing waste salt are carried out at a temperature of 25-35℃ and a pH of 3-5. The amount of the first oxidant added is 0.01%-3% of the mass of the phosphorus-containing waste salt; The amount of modified activated carbon added is 0.01%-0.1% of the mass of the filtrate.

6. The method for synergistic synthesis of ferric phosphate using phosphorus-containing waste salt and iron-containing waste acid according to claim 1, characterized in that, The amount of iron added is 1%-2% of the mass of iron in the iron-containing waste acid; The precipitation of impurities was carried out at a pH of 4.0-5.5; The chitosan-sodium alginate composite flocculant is added at a dosage of 0.05-0.1 g / L.

7. The method for synergistic synthesis of ferric phosphate using phosphorus-containing waste salt and iron-containing waste acid according to claim 1, characterized in that, The phosphate purification solution and the ferrous purification solution are mixed at a P to Fe molar ratio of 0.95-1.05:

1. The amount of the second oxidant added is 1.0-1.5 times the theoretical oxygen demand; The oxidation reaction is carried out at a pH of 1.5-3.5 and a temperature of 40-80℃ for 2-6 hours.

8. The method for synergistic synthesis of ferric phosphate using phosphorus-containing waste salt and iron-containing waste acid according to claim 1, characterized in that, The process to obtain ferric phosphate includes washing, drying, and heat treatment, wherein the heat treatment is carried out at 500-700℃ for 2-6 hours.

9. The method for synergistic synthesis of ferric phosphate using phosphorus-containing waste salt and iron-containing waste acid according to any one of claims 1-8, characterized in that, When mixing the phosphate purification solution, the ferrous purification solution, and the second oxidant, 0.05%-0.2% by weight of the ferrous purification solution of polyethylene glycol is also added, wherein the molecular weight of the polyethylene glycol is 1000-4000. The phosphate purification solution, ferrous purification solution, and second oxidant are mixed in a parallel flow ratio of 0.9-1.1:0.8-1.0:0.1-0.2, with a total feeding time of 1-2 hours. After collecting the insoluble matter, the separated reaction mother liquor is further purified to recover salt and reuse the solvent.

10. A type of iron phosphate, characterized in that, The method described in any one of claims 1-9 for the synergistic synthesis of ferric phosphate using phosphorus-containing waste salt and iron-containing waste acid is employed.

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