Process for the preparation of iron phosphate from rust

Abstract

The application discloses a method for preparing iron phosphate from rust iron, and relates to the technical field of resource recycling and comprehensive utilization. The method comprises the following steps: taking rust iron as an iron source to carry out purification and chemical reaction, preparing a high-purity iron solution, and then reacting the iron solution with a phosphate to prepare iron phosphate. Specifically, the method comprises the following steps: (1) acid immersion and filtration; (2) oxidation of the iron solution; (3) iron precipitation by adding phosphorus; (4) filtration and washing; (5) heat preservation and crystallization; and (6) high-temperature calcination. The method widens the recycling and utilization channels of rust iron resources, and enriches the preparation paths of iron phosphate. The method overcomes the problem of calcium-containing solid generation in the rust iron resource utilization process. Compared with common iron resource utilization processes for preparing iron phosphate, the preparation process of the application is short and simple to operate, and the efficient utilization of rust iron resources is realized to prepare high-economic-value iron phosphate.

Description

Technical Field

[0001] This invention specifically relates to the field of waste resource recycling and comprehensive utilization technology, and more specifically, to a method for preparing ferric phosphate from rusted iron. Background Technology

[0002] Iron phosphate (FeFe) is an important inorganic material with good chemical stability and acid / alkali resistance, and is widely used in catalysts and pigments. Furthermore, olivine-structured FeFe exhibits excellent electrochemical energy storage activity and stability, making it widely applicable in electric vehicles and energy storage systems. In recent years, with the rapid development of new energy electric vehicles and energy storage batteries, the market demand for lithium-ion battery materials has gradually increased, especially for related cathode materials such as lithium iron phosphate. FeFe is one of the precursors for preparing lithium iron phosphate, and its manufacturing cost significantly influences the overall cost of lithium iron phosphate.

[0003] Currently, the preparation of iron phosphate from different iron sources mainly focuses on the following methods: (1) Acid leaching of iron powder to obtain Fe(II) solution, adding phosphoric acid and oxidant and mixing evenly, then adding alkali solution to adjust pH to obtain iron phosphate. This method has strict requirements on the purity of raw materials and has a high cost; (2) High-temperature calcination of industrial waste iron to obtain iron oxide, adding phosphoric acid for acid leaching to obtain Fe(III) solution, then adding alkali solution to adjust pH to obtain iron phosphate. The iron phosphate prepared by this method has a low purity; (3) Acid leaching of iron-containing minerals to obtain acid leaching solution, adding alkali solution to adjust pH to obtain iron phosphate. This method faces problems such as excessive impurity metal ions and low product purity.

[0004] The choice of iron source largely determines the quality of the finished ferric phosphate product. Therefore, developing a more cost-effective, environmentally friendly, and stable iron source for ferric phosphate preparation is of great significance. Rusty iron, a ubiquitous waste in industry and daily life, mainly consists of iron, ferric oxide, and other impurity ions. Its indiscriminate disposal not only wastes resources but also causes environmental pollution. The recycling of iron resources is crucial for sustainable social development, and proper handling of rusty iron in daily life can achieve environmental beautification and resource recycling. Therefore, developing a low-cost, high-purity ferric phosphate preparation method using rusty iron as the iron source has significant economic and environmental value. Summary of the Invention

[0005] The purpose of this invention is to provide a low-cost, resource-efficient method for preparing iron phosphate. This method can effectively utilize iron products (containing a large amount of rust iron components) that have been decommissioned due to corrosion or oxidation in daily life, while improving the economic benefits of iron phosphate, reducing production costs, and alleviating environmental pollution pressure.

[0006] To achieve the above effects, the present invention provides the following technical solution: using rusted iron as the iron source for purification and chemical reaction to obtain a high-purity iron solution, and then reacting the iron solution with phosphate to obtain iron phosphate. Specifically, the following steps are included: (1) acid leaching and filtration; (2) iron oxide solution; (3) phosphorus addition to precipitate iron; (4) filtration and washing; (5) heat preservation and crystallization; (6) high-temperature calcination.

[0007] The preparation method of the present invention has the following advantages:

[0008] (a) Iron phosphate is prepared by using iron products (mainly rusted iron) that have been decommissioned due to corrosion or oxidation in daily life as an iron source, which effectively utilizes iron resources, enhances the utilization value of rusted iron, and alleviates the environmental pollution problem caused by rusted iron.

[0009] (b) By using a complexing agent to specifically complex impurity metal ions and purify the molten iron, the interference of impurity metal ions is reduced during the subsequent pH adjustment process to generate ferric phosphate, thereby obtaining a pure ferric phosphate product. This optimizes the synthesis method and the impurity metal ion removal strategy.

[0010] (c) Compared with general solid waste utilization processes, this process avoids the introduction or generation of difficult-to-treat calcium-containing solid precipitates; compared with the iron source for traditional synthesis of iron phosphate, this iron source has lower cost, higher element utilization rate, simpler process, easier operation, and higher economic benefits. Attached Figure Description

[0011] Appendix Figure 1 This is a process flow diagram of the present invention;

[0012] Appendix Figure 2 This is the XRD pattern of the iron phosphate product of Example 1 of the present invention. Detailed Implementation

[0013] The specific steps of the present invention include: (1) acid leaching and filtration; (2) iron oxide liquid; (3) phosphorus addition and iron precipitation; (4) filtration and washing; (5) heat preservation and crystallization; and (6) high-temperature calcination.

[0014] The main impurity elements in the rusted iron used in the following embodiments of the present invention are shown in Table 1 below:

[0015] Table 1. Content of major impurity elements in rust iron

[0016]

[0017] Specifically, the steps are as follows:

[0018] (1) Acid leaching and filtration: The rusted iron is soaked in an acid solution and then filtered to obtain an acid-soluble filtrate;

[0019] (2) Iron oxide liquid: Iron oxide liquid is obtained by oxidizing the acid-dissolved filtrate with an oxidizing agent;

[0020] (3) Phosphorus addition and iron precipitation: After adding phosphorus source to iron oxide liquid, precipitation is carried out to obtain precipitated slurry;

[0021] (4) Filtration and washing: The precipitated slurry is filtered and washed to obtain filter cake;

[0022] (5) Heat preservation and crystallization: The filter cake is subjected to crystallization treatment;

[0023] (6) High-temperature calcination: The crystallized product is calcined to obtain iron phosphate.

[0024] Regarding the above steps, step (1) acid leaching and filtration: rusted iron is soaked in an acid solution with a concentration of 2-4 mol / L at a temperature of 60-85 °C. The selected acid is one or more of hydrochloric acid, sulfuric acid, and nitric acid. The complexing agent used is one or more of dimercaprol, sodium dimercaptopropanesulfonate, sodium dimercaptosuccinate, penicillamine, acetylpenicillamine, mercaptopropane, and polythiol resin, with an addition amount of 0.4% of the solution mass. After acid leaching for 3-5 h, the solution is filtered to obtain the acid-soluble filtrate.

[0025] (2) Iron oxide liquid: An oxidant is added to the above filtrate. The oxidant is at least one of hydrogen peroxide, sodium hypochlorite or hypochlorous acid. The ratio of the amount of the oxidant to the amount of iron in the filtrate is 0.2-0.6:1.

[0026] (3) Phosphorus addition and iron precipitation: A phosphorus source, at least one of phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, or sodium phosphate, is added to the above solution. The molar ratio of the phosphate salt to the iron in the acid-dissolving filtrate is 0.97-1.01:1. The pH of the system is adjusted to 2.2-3.2 using 1.4 mol / L sodium hydroxide to allow for complete reaction and obtain a precipitated slurry.

[0027] (4) Filtration and washing: The above precipitated slurry is filtered, and the filter cake is washed with pure water until the conductivity of the wash water is ≤1000 μS / cm. The filtrate is then treated to obtain sodium chloride.

[0028] (5) Heat preservation crystallization: The above filter cake is subjected to crystallization treatment at a temperature of 80-90 °C for 4-5 hours.

[0029] (6) High-temperature calcination: The crystallized product is calcined at a temperature of 600-800 °C for 2-6 hours.

[0030] The following is combined with Figure 1 The invention will be explained in more detail through examples.

[0031] Example 1

[0032] A method for preparing ferric phosphate from rusted iron:

[0033] (1) Acid leaching and filtration

[0034] Rusty iron was soaked in 3 mol / L hydrochloric acid at 75 °C, and 0.4% sodium dimercaptosuccinate (a complexing agent by mass) of the solution was added. After acid soaking for 4 hours, the solution was filtered to obtain the acid-soluble filtrate.

[0035] The content of impurity elements in the acid-dissolving filtrate is shown in Table 2 below.

[0036] Table 2 Impurity content in filtrate

[0037]

[0038] As shown in Table 2, the main impurity elements in the filtrate are Na: 503.6 ppm, Mn: 269.3 ppm, Al: 384.1 ppm, Zn: 106.3 ppm, and Ni: 112.4 ppm. After the complexing agent captures the heavy metal ions, the contents of Cr, Cu, and Cd metal ions reach a low level. In addition, since C is insoluble in acid, it is separated from the filtrate after filtration.

[0039] (2) Iron oxide solution: Add 30% hypochlorous acid to the above filtrate. The ratio of the amount of hypochlorous acid to the amount of iron in the filtrate is 0.4:1.

[0040] (3) Phosphorus addition to precipitate iron: Add a phosphorus source to the above solution, with the ratio of disodium hydrogen phosphate to iron in the acid filtrate being 0.99:1. Adjust the pH of the system to 2.6 using 1.4 mol / L sodium hydroxide to allow the reaction to proceed fully and obtain a precipitated slurry.

[0041] (4) Filtration and washing: Filter the above precipitated slurry and wash the filter cake with pure water until the conductivity of the wash water is ≤1000μS / cm (935 μS / cm in this test). Sodium chloride is obtained by treating the filtrate.

[0042] (5) Insulation and crystallization: The above filter cake is crystallized at a temperature of 90 °C for 4 h.

[0043] (6) High-temperature calcination: The crystallized product was calcined at 725 °C for 3 h. The elemental analysis of the impurities in the ferric phosphate is shown in Table 3 below.

[0044] Table 3 Impurity content in ferric phosphate

[0045]

[0046] A comparison of Tables 3 and 2 shows that after steps (2)-(6), the content of various impurities in the obtained ferric phosphate is significantly reduced. The main impurities, Mn, Al, Zn, and Ni ions, are separated from the filtrate and product during the pH adjustment step; Na ions have high water solubility and are separated from the ferric phosphate in the subsequent washing step, thus obtaining a ferric phosphate product with low impurity content. The XRD of the ferric phosphate prepared by Example 1 is shown below. Figure 2 As shown, the sample has high crystallinity and no obvious impurity peaks, proving that the prepared iron phosphate has high purity and quality.

[0047] Examples 2-4

[0048] These examples illustrate the method for preparing battery-grade iron phosphate using rusted iron provided by the present invention.

[0049] Example 2 used penicillamine, Example 3 used mercaptopropane, and Example 4 used sodium dimercaptopropanesulfonate. The specific conditions and parameters for each step are shown in Table 4. Other methods are the same as in Example 1.

[0050] Table 4 Parameters and Conditions for Each Embodiment

[0051]

[0052] Comparative Example 1

[0053] In this comparative example, pure iron powder was used instead of the iron source in step (1), and no complexing agent was added. Otherwise, the iron phosphate material was prepared using the same parameters and conditions as in steps (1) to (6) of Example 1.

[0054] Comparative Example 2

[0055] In this comparative example, no complexing agent was added in step (1), and the other steps were the same as in Example 1.

[0056] The prepared iron phosphate materials are characterized and analyzed below.

[0057] The iron phosphate materials prepared in Examples 1-4 and the comparative examples were tested, and the results are shown in Table 5. D50 was measured using a Malvern 3000 laser particle size analyzer; specific surface area was obtained using a McMurray Tick 3030 instrument.

[0058] Table 5. Detection results of ferric phosphate in the examples and comparative examples.

[0059]

[0060] As can be seen from the results in Table 5, the content of each impurity in the iron phosphate material prepared using the method provided by this invention (Examples 1-4) is close to that in the iron phosphate material prepared using iron powder as the iron source; and the Fe and P content, specific surface area, D50, and other indicators are close to those in Comparative Example 1, which uses pure iron powder as the iron source. In contrast, in Comparative Example 2, which did not use a complexing agent, heavy metal elements in the rusted iron could not be sufficiently removed during the preparation process, resulting in a large amount of residue in the iron phosphate product and poor product purity. This demonstrates that the method provided by this invention, using rusted iron as the iron source, and through purification and physical and chemical reaction processes, can prepare high-quality iron phosphate material with low impurity content.

[0061] Although the present invention has been described in as much detail as possible above using general descriptions, specific embodiments, and experiments, improvements or modifications to some processes based on the present invention will be obvious to those skilled in the art. Therefore, any modifications or improvements that do not involve inventiveness and are made without departing from the essential basis of the present invention are within the scope of protection claimed by the present invention.

Claims

1. A method for preparing ferric phosphate from rusted iron, characterized in that, Includes the following steps: (1) Acid leaching and filtration: The rusted iron is leached in an acid solution at a temperature of 60-85 °C with the addition of a complexing agent for 3-5 h, and then filtered to obtain an acid-soluble filtrate. The complexing agent is one or more of dimercaprol, sodium dimercaptopropanesulfonate, sodium dimercaptosuccinate, penicillamine, acetylpenicillamine, mercaptopropane, and polythiol resin. (2) Iron oxide solution: Add an oxidizing agent to the acid-dissolved filtrate to oxidize and obtain iron oxide solution; (3) Phosphorus addition to precipitate iron: Add phosphorus source to iron oxide liquid and precipitate to obtain precipitate slurry; (4) Filtration and washing: The precipitated slurry is filtered and washed to obtain filter cake; (5) Heat preservation and crystallization: The filter cake is subjected to crystallization treatment; (6) High-temperature calcination: The crystallized product is calcined to obtain iron phosphate.

2. The method for preparing ferric phosphate according to claim 1, characterized in that, In step (1), the acid solution is one or more of hydrochloric acid, sulfuric acid, and nitric acid with a concentration of 2-4 mol / L.

3. The method for preparing ferric phosphate according to claim 1, characterized in that, In step (2), the oxidant is one of hydrogen peroxide, sodium hypochlorite or hypochlorous acid, and the ratio of the amount of the oxidant to the amount of iron in the filtrate is 0.2 to 0.6:

1.

4. The method for preparing ferric phosphate according to claim 1, characterized in that, In step (3), the phosphorus source is one of phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, or sodium phosphate; and sodium hydroxide is used to adjust the pH of the system to 2.2-3.2 to fully react and obtain a precipitated slurry.

5. The method for preparing ferric phosphate according to claim 4, characterized in that, The ratio of the amount of phosphorus in the phosphorus source to the amount of iron in the acid filtrate is 0.97-1.01:

1.

6. The method for preparing ferric phosphate according to claim 1, characterized in that, In step (4), the washing medium is pure water, and the washing is performed until the conductivity of the washing water is ≤1000 μS / cm.

7. The method for preparing ferric phosphate according to claim 1, characterized in that, In step (5), the crystallization temperature is 80-90 °C and the holding time is 4-5 h.

8. The method for preparing ferric phosphate according to claim 1, characterized in that, In step (6), the calcination temperature is 600-800 °C and the time is 2-6 h.

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