Method for preparing iron phosphate by hydrogen-based micro-reduction roasting reinforced iron ore acid dissolution

Abstract

The invention discloses a method for preparing iron phosphate through hydrogen-based micro-reduction roasting reinforced iron ore acid dissolution. The method comprises the following steps that (1) iron ore is pretreated into iron ore powder with D90 smaller than 74 micrometers; (2) hydrogen is introduced into the iron ore powder within the temperature range of 700-900 DEG C for micro-reduction roasting, the hydrogen flux of each kilogram of iron ore is 10-60 L / min, the roasting time is 5-30 min, and micro-reduction iron ore powder is obtained after cooling; (3) adding the micro-reduced iron ore powder into a mixed acid solution, adding a proper amount of a hydrogen peroxide solution, stirring and leaching at a set temperature to obtain a leaching mixed solution, and carrying out solid-liquid separation on the leaching mixed solution to obtain leaching residues and a leaching solution; (4) adjusting the pH value of the leachate, heating to a preset temperature, carrying out auxiliary stirring reaction, aging and filtering to obtain crude iron phosphate; and (5) calcining the crude iron phosphate, and cooling to obtain the battery-grade iron phosphate. By means of the method, the acid dissolution efficiency of the iron ore can be effectively improved, acid consumption and energy consumption are reduced, meanwhile, green production can be achieved, and the requirement for sustainable development is met.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metallurgy and mineral processing, and relates to a method for preparing iron phosphate from hydrogen-based micro-reduction roasting and strengthened acid dissolution of iron ore. BACKGROUND

[0002] Lithium iron phosphate (LiFePO4) as a new type of lithium-ion battery cathode material, due to its excellent cycle stability, safety and environmental friendliness, has become the preferred material in the field of electric vehicles, grid energy storage and portable electronic devices. Compared with traditional lithium-ion batteries, lithium iron phosphate batteries have longer service life, higher safety and lower cost. However, the performance of lithium iron phosphate is highly dependent on the quality of its precursor, iron phosphate (FePO4). High-purity iron phosphate with excellent physical and chemical properties is a basic material for producing high-performance lithium iron phosphate. Therefore, how to economically and efficiently prepare battery-grade iron phosphate has become the key to research.

[0003] Traditionally, high-purity chemical reagents such as ferrous sulfate (FeSO4) or iron oxide (Fe2O3) are used as iron sources for the preparation of iron phosphate. However, the production cost of these chemical reagents is high, and the preparation process often involves a large amount of chemical reagents and steps, generating a large amount of chemical waste liquid, increasing environmental pressure and production cost. Therefore, the use of iron ore as an iron source to prepare iron phosphate has gradually attracted the attention of researchers due to its abundant resources and low price. However, the use of iron ore as an iron source has a series of technical problems, especially the difficulty in effectively destroying the crystal structure of oxidized iron ore (such as hematite and magnetite), which leads to poor dissolution performance in acidic solution, thereby limiting its application in the preparation of iron phosphate.

[0004] Oxidized iron ore (Fe2O3, Fe3O4) has a very dense crystal structure, and iron ions are firmly bound in the crystal lattice, making it difficult to dissociate in an acidic medium. Hematite and magnetite are typical oxidized iron minerals, and the strong iron-oxygen bond in their crystal structure makes it difficult for acid to effectively penetrate and react with iron ions under normal conditions. This dense structure results in a very low dissolution rate of iron ore during acid dissolution, requiring higher temperatures and longer reaction times to achieve partial dissolution. Especially in the process of preparing high-purity iron phosphate, low dissolution rate not only increases the consumption of acid, but also leads to high production energy consumption and low iron extraction rate. In addition, iron in oxidized iron minerals mainly exists in the form of Fe 3+ , which has weak solubility in acidic environments. In contrast, Fe 2+ ions are more easily dissolved, but traditional acid dissolution processes are difficult to directly reduce Fe 3+ to Fe 2+, which further aggravates the difficulty of iron ore dissolution. To improve the acid dissolution efficiency of oxidized iron ore, traditional processes often use high-temperature roasting or add reducing agents to destroy the crystal structure or reduce the valence of iron. However, these methods often consume a large amount of energy and produce harmful greenhouse gases, making it difficult to meet the requirements of modern green and environmentally friendly production.

[0005] In recent years, hydrogen reduction technology has gradually become a research hotspot for improving the acid dissolution efficiency of oxidized iron ore as a green and environmentally friendly mineral processing technology. As a clean reducing agent, hydrogen does not produce harmful gases during the reduction process, and the only byproduct is water. Through the reduction of hydrogen, the valence of iron ions in oxidized iron ore can be effectively reduced, and part of the Fe 3+ is reduced to Fe 2+ , thereby significantly improving the solubility of iron ore in acid. In addition, hydrogen reduction during roasting can also destroy the dense crystal structure of iron ore, increasing the specific surface area of the ore, allowing acid to penetrate and react with iron ions more effectively, thereby further improving the dissolution efficiency. SUMMARY

[0006] In view of the shortcomings of the prior art, the purpose of the present application is to provide a method for preparing iron phosphate by hydrogen-based micro-reduction roasting and strengthening acid dissolution of iron ore. The method can effectively improve the acid dissolution efficiency of iron ore, reduce acid consumption and energy consumption, and help achieve green production, meeting the requirements of sustainable development.

[0007] To achieve the above purpose, the present application provides a method for preparing iron phosphate by hydrogen-based micro-reduction roasting and strengthening acid dissolution of iron ore, comprising the following steps:

[0008] (1) pretreating iron ore into iron ore powder with a particle size of D 90 <74μm;

[0009] (2) passing hydrogen into the iron ore powder obtained in step (1) for micro-reduction roasting at a temperature range of 700-900℃, the hydrogen flux per kilogram of iron ore being 10-60L / min, and the roasting time being 5-30 minutes, and obtaining micro-reduced iron ore powder after cooling;

[0010] (3) adding the micro-reduced iron ore powder obtained in step (2) into a mixed acidic solution and adding an appropriate amount of hydrogen peroxide solution, stirring and leaching at a set temperature to obtain a leaching mixture, and performing solid-liquid separation on the leaching mixture to obtain leaching residue and leaching solution;

[0011] (4) adjusting the pH of the leaching solution obtained in step (3), heating to a predetermined temperature, and assisting in stirring reaction, and then aging, filtering to obtain crude iron phosphate;

[0012] (5) calcining the crude iron phosphate obtained in step (4) and cooling to obtain battery-grade iron phosphate.

[0013] Preferably, in step (1), the mass fraction of iron in the iron ore is ≥45wt.%.

[0014] Preferably, in step (2), the protective atmosphere during the heating and cooling process is nitrogen or argon.

[0015] Preferably, in step (3), the mixed acid solution is a mixture of one or more of sulfuric acid, hydrochloric acid, acetic acid, nitric acid, phosphoric acid, and phosphate, and the phosphate is a mixture of one or more of ammonium phosphate, monobasic ammonium phosphate, and dibasic ammonium phosphate.

[0016] Further, in step (3), the H + The concentration of the mixed acid solution is 3-8mol / L, the liquid-solid ratio of the mixed acid solution to the micro-reduced iron ore powder is 3-8:1, the molar ratio of phosphorus in the mixed acid solution to iron in the micro-reduced iron ore powder is 0.95-1.1:1, the molar ratio of hydrogen peroxide to iron in the micro-reduced iron ore powder is 0.1-0.5:1, the leaching temperature is 40-90℃, and the stirring time is 10-120min.

[0017] Preferably, in step (4), the pH adjuster is a mixture of one or more of ammonia and sodium hydroxide, the pH of the leaching solution is adjusted to 1.6-2.6, the heating temperature is 30-80℃, the heating and stirring time is ≥10min, and the aging time is 10-60min.

[0018] Preferably, in step (5), the calcination temperature is 550-750℃, and the calcination time is 1-4h.

[0019] The present application proposes a technology combining hydrogen micro-reduction and expansion roasting, by controlling the hydrogen reduction conditions and the roasting temperature, so that the iron ore undergoes microstructure expansion and reduction of Fe 3+ to Fe 2+ in the roasting process. The expansion roasting process effectively increases the specific surface area of the mineral, enhances the permeability of the acid and the solubility of the iron, thereby improving the efficiency of acid dissolution of the iron ore and providing an efficient and economical process route for preparing high-purity battery-grade iron phosphate. This method not only realizes efficient utilization of iron ore resources, but also meets the production requirements of green environmental protection, significantly reducing the cost of preparing lithium iron phosphate positive electrode material.

[0020] Compared with the existing technology, the present application has the following advantages:

[0021] 1) Improve the efficiency of acid dissolution of iron ore: the present application successfully solves the problem of difficult dissolution of iron oxide ore (such as hematite and magnetite) by combining hydrogen micro-reduction and expansion roasting technology. Hydrogen not only reduces Fe3+ to Fe 2+ The expansion of iron minerals also destroys their crystal structure, increasing the specific surface area of the minerals. This structural change significantly improves the contact efficiency between iron ore and acid solution, allowing the iron in the ore to dissolve more quickly and completely, greatly increasing the dissolution rate. Compared with traditional acid dissolution methods, the process of the present invention significantly improves the extraction rate of iron while reducing reaction time, and is particularly suitable for preparing high-purity iron phosphate.

[0022] 2) Reducing acid consumption and energy consumption: Traditional iron ore acid dissolution processes usually require high acid concentration and long dissolution time, resulting in high acid consumption and high energy consumption. By optimizing the hydrogen micro-reduction roasting conditions, the present invention effectively reduces the difficulty of acid dissolution, allowing the iron ore to be efficiently dissolved at lower acid concentration and lower temperature, significantly reducing the amount of acid consumed. In addition, the expansion effect during roasting increases the reactivity of the iron ore, thereby reducing the required roasting temperature and time and reducing the energy consumption during roasting. This process can effectively reduce the production cost of iron phosphate, making it more valuable for industrial application.

[0023] 3) Green and environmentally friendly: The present invention uses hydrogen as a reducing agent, avoiding the production of greenhouse gases and harmful emissions such as carbon dioxide and sulfur dioxide during traditional carbon-based reduction roasting (such as coke, natural gas, etc.). The byproduct of hydrogen reduction is only water, and there is no harmful gas emission during roasting, meeting the environmental protection requirements of current green chemical and green metallurgy. In addition, the amount of waste liquid generated by the optimized acid dissolution process is also controlled, reducing the treatment cost and environmental pressure of waste acid liquid. This process helps to achieve green production while reducing energy consumption, meeting the requirements of sustainable development.

[0024] 4) Low-cost iron source utilization: The present invention uses inexpensive and readily available iron ore (such as hematite or magnetite) instead of traditional high-cost iron salts as the iron source, greatly reducing the raw material cost of iron phosphate. Iron ore resources are widely available, abundant in reserves, and relatively low in price, making the process of the present invention particularly suitable for large-scale industrial production, which can significantly reduce the production cost of battery-grade iron phosphate. Compared with preparation methods that rely on high-purity chemical iron sources, the low-cost iron source utilization of the present invention significantly reduces the overall manufacturing cost of lithium iron phosphate batteries, facilitating the popularization and application of lithium iron phosphate batteries. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings and tables needed in the embodiment or prior art description. Obviously, the drawings described below are only some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without creating any inventive effort.

[0026] Figure 1 Process flow chart of the present application. DETAILED DESCRIPTION

[0027] The following is a specific implementation case given by the inventor, it is necessary to explain that these examples are only to better illustrate the present application, and not used to limit the scope of the present application. Any parameter selection within the scope of the present application is within the scope of the present application.

[0028] The following is further illustrated by specific examples and drawings.

[0029] Example 1

[0030] A method for preparing iron phosphate from a hydrogen-based micro-reduction roasting enhanced iron ore acid dissolution, comprising:

[0031] Grinding the iron ore to D 90 <74μm iron ore powder, roasting the iron ore powder at 825℃ with a hydrogen flux of 40L / min per kg of iron ore for 15 minutes, and cooling to obtain micro-reduced iron ore powder. The protective atmosphere during heating and cooling is N2;

[0032] After cooling the micro-reduced iron ore powder, add a mixed acid solution of hydrochloric acid and phosphoric acid, the H + The concentration of the mixed acid solution is 6mol / L, the liquid-solid ratio is 6:1, the molar ratio of phosphorus in the mixed acid solution to iron in the micro-reduced iron ore powder is 1:1, the molar ratio of hydrogen peroxide to iron in the reduced iron powder is 0.35:1, the leaching temperature is 70℃, the stirring time is 40min, the leaching mixture is subjected to solid-liquid separation to obtain leaching residue and leaching solution;

[0033] Add ammonia water to the leaching solution to adjust the pH of the leaching solution to 2.0, heat to 60℃, stir for 20min, and age for 30min, then filter to obtain crude iron phosphate, calcine the crude iron phosphate at 700℃ for 2h, and cool to obtain battery-grade iron phosphate. The iron leaching rate using this method is 98.64%.

[0034] Table 1 is the composition of the iron ore in Example 1

[0035]

[0036] Table 2 shows that the iron phosphate product prepared in Example 1 meets the standard requirements of 《HG / T 4701-2021 Iron Phosphate for Batteries》, with a purity of 99.67%.

[0037] Table 2 Standard requirements of 《HG / T 4701-2021 Iron Phosphate for Batteries》 and elemental content of iron phosphate product

[0038]

[0039] Example 2

[0040] A method for preparing iron phosphate from hydrogen-based micro-reduced roasting enhanced iron ore acid dissolution, comprising:

[0041] Grinding the iron ore (same as in Example 1) to D 90 <74μm of iron ore powder, roasting the iron ore powder at 800℃ with a hydrogen flux of 50L / min per kg of iron ore for 15 minutes, and obtaining micro-reduced iron ore powder after cooling, with N2 as the protective atmosphere during the heating and cooling processes;

[0042] After cooling the micro-reduced iron ore powder, adding a mixed acidic solution of hydrochloric acid and phosphoric acid, the H + concentration of the mixed acidic solution is 6mol / L, the liquid-solid ratio is 6:1, the molar ratio of phosphorus in the mixed acidic solution to iron in the micro-reduced iron ore powder is 0.98:1, the molar ratio of hydrogen peroxide to iron in the reduced iron powder is 0.4:1, the leaching temperature is 90℃, the stirring time is 40min, and the leaching mixture is subjected to solid-liquid separation to obtain leaching residue and leaching solution;

[0043] Adjusting the pH of the leaching solution to 2.0 by adding ammonia water, heating at 70℃ for 20min, and aging for 30min, and filtering to obtain crude iron phosphate, calcining the crude iron phosphate at 650℃ for 2h, and obtaining battery-grade iron phosphate after cooling, with an iron leaching rate of 91.98% using this method.

[0044] Table 3 shows that the elemental content and phosphorus-iron ratio of the iron phosphate product prepared in Example 2 meet the standard requirements of “HG / T 4701-2021 Iron Phosphate for Batteries”, with a purity of 97.59%.

[0045] Table 3 Standard requirements of “HG / T 4701-2021 Iron Phosphate for Batteries” and elemental content of iron phosphate product

[0046]

[0047] Example 3

[0048] A method for preparing iron phosphate from hydrogen-based micro-reduced roasting enhanced iron ore acid dissolution, comprising:

[0049] Grinding the iron ore (same as in Example 1) to D 90 <74μm of iron ore powder, roasting the iron ore powder at 800℃ with a hydrogen flux of 50L / min per kg of iron ore for 15 minutes, and obtaining micro-reduced iron ore powder after cooling, with N2 as the protective atmosphere during the heating and cooling processes;

[0050] The reduced iron ore powder is added into a mixed acid solution of hydrochloric acid and phosphoric acid after cooling, the concentration of H + The concentration of the mixed acid solution is 7 mol / L, the liquid-solid ratio is 5:1, the molar ratio of phosphorus in the mixed acid solution to iron in the reduced iron ore powder is 1.02:1, the molar ratio of hydrogen peroxide to iron in the reduced iron powder is 0.4:1, the leaching temperature is 70°C, and the stirring time is 80 min. The leaching mixture is subjected to solid-liquid separation to obtain leaching residue and leaching solution.

[0051] Ammonia water is added to the leaching solution to adjust the pH of the leaching solution to 2.0, the heating temperature is 80°C, heating and stirring for 30 min, aging for 30 min, and filtering to obtain crude iron phosphate. The crude iron phosphate is calcined at 700°C for 3 h, and the battery-grade iron phosphate is obtained after cooling. The iron leaching rate of this method is 90.69%.

[0052] Table 4 shows that the elemental content and the phosphorus-iron ratio of the iron phosphate product prepared in Example 3 meet the standard requirements of HG / T 4701-2021 Battery Iron Phosphate, and the purity is 97.28%.

[0053] Table 4 shows the standard requirements of HG / T 4701-2021 Battery Iron Phosphate and the elemental content of the iron phosphate product.

[0054]

[0055] Comparative Example 1

[0056] An iron ore acid dissolution process for preparing battery-grade iron phosphate includes:

[0057] The iron ore (same as Example 1) is ground to an iron ore powder with D90 < 74 μm. The iron ore powder is calcined at a temperature of 800°C with N2 without hydrogen, and the calcination time is 40 minutes to obtain reduced iron ore powder.

[0058] The calcined iron ore powder is added into a mixed acid solution of hydrochloric acid and phosphoric acid after cooling, the concentration of H + The concentration of the mixed acid solution is 4 mol / L, the liquid-solid ratio is 4:1, the molar ratio of phosphoric acid to iron in the titanium-iron slag raw material is 1:1, and the leaching mixture is obtained after heating and stirring at 90°C for 120 min. The leaching mixture is subjected to solid-liquid separation to obtain leaching residue and leaching solution.

[0059] Ammonia water is added to the leaching solution to adjust the pH of the leaching solution to 2.0, the heating temperature is 60°C, heating and stirring for 20 min, aging for 30 min, and filtering to obtain crude iron phosphate. The crude iron phosphate is calcined at 700°C for 2 h, and the iron phosphate is obtained after cooling. The iron leaching rate of this method is 50.23%, the purity of the iron phosphate is 80.22%, and Fe / P = 0.814.

[0060] The iron phosphate product prepared in Comparative Example 1 does not meet the requirements of the standard HG / T 4701-2021 Iron Phosphate for Batteries.

[0061] Table 5 Standard requirements of HG / T 4701-2021 Iron Phosphate for Batteries and elemental content of iron phosphate product

[0062]

[0063] In Examples 1 and 2, hydrogen gas plays a key role as a reducing agent during the process of micro-reduction expansion roasting. Hydrogen gas can effectively reduce Fe 3+ to Fe 2+ in iron ore at high temperature. Fe 2+ is more easily dissolved in an acidic environment, which significantly improves the dissolution efficiency of iron ore. In addition, the hydrogen reduction reaction is accompanied by the expansion effect of iron ore, which destroys the dense crystal structure of iron ore minerals, increases the specific surface area of the ore, and enhances the contact efficiency of acid solution and ore. This series of microstructure changes greatly improves the solubility of iron ore in acid, and significantly increases the iron leaching rate.

[0064] In Comparative Example 1, since hydrogen gas is not introduced, Fe 3+ in iron ore is not reduced to easily soluble Fe 2+ , and the crystal structure of iron ore remains relatively intact, making it difficult for acid solution to effectively penetrate and react, resulting in a significant decrease in iron leaching rate. This shows that hydrogen reduction not only improves the valence state distribution of iron, but also greatly enhances the reactivity of iron ore through the structure expansion effect, making the dissolution process more efficient.

[0065] Hydrogen gas as a reducing agent does not produce harmful gases during roasting, and the roasted iron ore undergoes expansion and micro-reduction, significantly increasing the specific surface area of the mineral and partially reducing Fe 3+ to easily soluble Fe 2+ , thereby improving the solubility of iron ore. The method of the present application optimizes the roasting and dissolution conditions, realizes the efficient utilization of iron ore resources, and provides an efficient way for the low-cost and environmentally friendly preparation of battery-grade iron phosphate. The present application also aims to simplify the preparation process of iron phosphate, so that low-cost raw materials-iron ore can be used to produce battery-grade iron phosphate materials. Through the process of the present application, the production cost can be greatly reduced, the generation of chemical waste liquid can be reduced, and at the same time the iron phosphate material has excellent purity and physical and chemical properties, which is suitable for large-scale industrial production, and helps the promotion and application of lithium iron phosphate batteries.

[0066] The preferred embodiments of the present application are described in detail above, but the embodiments of the present application are not limited to the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application should be equivalent replacement methods, and are included in the protection scope of the present application.

Claims

1. A method for preparing ferric phosphate by hydrogen-based micro-reduction roasting and intensified acid dissolution of iron ore, characterized in that: The following steps are involved: (1) Pre-processing the iron ore into D 90 Iron ore fines <74μm; (2) the iron ore powder obtained in step (1) is subjected to slight reduction roasting by introducing hydrogen at a temperature range of 700 to 900° C., with a hydrogen flux of 10 to 60 L / min per kilogram of iron ore and a roasting time of 5 to 30 minutes, and then cooled to obtain slightly reduced iron ore powder; (3) adding the slightly reduced iron ore powder obtained in step (2) to a mixed acidic solution, and adding an appropriate amount of hydrogen peroxide solution, stirring and leaching at a set temperature to obtain a leaching mixture, and performing solid-liquid separation on the leaching mixture to obtain leaching residue and leachate; (4) adjusting the pH of the leachate obtained in step (3), heating it to a predetermined temperature, assisting the reaction with stirring, and then aging and filtering to obtain crude ferric phosphate; (5) calcining the crude iron phosphate obtained in step (4) and cooling it to obtain battery-grade iron phosphate.

2. The method for preparing ferric phosphate by hydrogen-based micro-reduction roasting and enhanced acid dissolution of iron ore according to claim 1, characterized in that: In step (1), the iron mass fraction in the iron ore is ≥45wt.%.

3. The method for preparing ferric phosphate by hydrogen-based micro-reduction roasting and strengthening acid dissolution of iron ore according to claim 1, characterized in that: In step (2), the protective atmosphere during the heating and cooling process is nitrogen or argon.

4. The method for preparing ferric phosphate by hydrogen-based micro-reduction roasting and enhanced acid dissolution of iron ore according to claim 1, characterized in that: In step (3), the mixed acidic solution is a mixture of one or more of sulfuric acid, hydrochloric acid, acetic acid, nitric acid, phosphoric acid, and phosphates, and the phosphate is a mixture of one or more of ammonium phosphate, ammonium monohydrogen phosphate, and ammonium dihydrogen phosphate.

5. The method for preparing ferric phosphate by hydrogen-based micro-reduction roasting and enhanced acid dissolution of iron ore according to claim 1 or 4, characterized in that: In step (3), H + The concentration is 3-8 mol / L, the liquid-solid ratio of the mixed acidic solution to the slightly reduced iron ore powder is 3-8:1, the molar ratio of phosphorus in the mixed acidic solution to the iron substance in the slightly reduced iron ore powder is 0.95-1.1:1, the molar ratio of hydrogen peroxide to the iron substance in the slightly reduced iron ore powder is 0.1-0.5:1, the leaching temperature is 40-100°C, and the stirring time is 10-120 minutes.

6. The method for preparing ferric phosphate by hydrogen-based micro-reduction roasting and enhanced acid dissolution of iron ore according to claim 1, characterized in that: In step (4), the pH adjuster is a mixture of one or more of ammonia water and sodium hydroxide, and the pH of the leachate is adjusted to 1.6-2.

6. The heating temperature is 30-80° C., the heating and stirring time is ≥10 min, and the aging time is 10-60 min.

7. The method for preparing ferric phosphate by hydrogen-based micro-reduction roasting and enhanced acid dissolution of iron ore according to claim 1, characterized in that: In step (5), the calcination temperature is 550-750° C., and the calcination time is 1-4 hours.

8. A battery-grade iron phosphate, characterized in that: The product is prepared by the method according to any one of claims 1 to 7.

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