A process for the co-production of battery grade iron phosphate and battery grade red iron oxide
By using a method for co-producing ferric phosphate and iron oxide red, and combining oxygen and ozone oxidation reactions with seed hydrolysis, the resource waste and purity/particle size control problems in the preparation of ferric phosphate and iron oxide red in existing technologies are solved, and a highly efficient and environmentally friendly co-production process is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- TIANJIN UNIV
- Filing Date
- 2026-05-06
- Publication Date
- 2026-06-09
AI Technical Summary
In existing technologies, the separate preparation of iron phosphate and iron oxide red has problems such as long process flow, low raw material utilization rate, and large amount of waste liquid, and it is difficult to achieve acid recycling and control of product purity and particle size.
A phosphorus-containing mixed acid is prepared by mixing sulfuric acid and phosphoric acid. Iron phosphate and iron oxide red are generated by oxidation reaction with oxygen and ozone. Combined with seed hydrolysis and mother liquor recycling, the co-production of iron phosphate and iron oxide red is achieved, and the particle size and purity of the products are controlled.
It achieves efficient utilization of iron, high product purity, uniform particle size, reduced water and energy consumption, and realizes resource recycling and product quality stability.
Smart Images
Figure CN122166835A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of new energy material preparation technology, specifically relating to a method for co-producing battery-grade iron phosphate and battery-grade iron oxide red. Background Technology
[0002] Lithium iron phosphate (LiFePO4), as a cathode material for lithium-ion batteries, boasts advantages such as high safety, long cycle life, and low cost, leading to its widespread application in electric vehicles and energy storage. Battery-grade iron phosphate is a key precursor in the preparation of lithium iron phosphate, and its purity and particle size directly affect the electrochemical performance of lithium iron phosphate. Iron oxide red (α-Fe2O3), not only a traditional pigment, has also been used in recent years as an iron source for the preparation of lithium iron phosphate; battery-grade iron oxide red requires high purity and a suitable particle size.
[0003] In existing technologies, ferric phosphate and iron oxide red are usually prepared separately, which results in problems such as long process flow, low raw material utilization, and large amounts of waste liquid generated. For example, the ammonia-based synthesis of ferric phosphate consumes as much as 150 m³ of water per ton of product. 3 The above methods generate a large amount of ammonia-containing wastewater. Iron oxide red is often prepared using the ferrous sulfate liquid-phase oxidation method, but the product purity is difficult to meet battery-grade requirements, and it is difficult to consistently obtain nanoscale particle sizes. Currently, there are no reported processes for the co-production of iron phosphate and iron oxide red while achieving acid recycling.
[0004] Therefore, developing a method that can simultaneously produce battery-grade iron phosphate and battery-grade iron oxide red, achieve resource recycling, reduce water consumption and costs, produce high-purity products, and flexibly control product particle size has significant industrial application value. Summary of the Invention
[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for co-producing battery-grade iron phosphate and battery-grade iron oxide red.
[0006] The technical solution of this invention is summarized as follows: A method for co-producing battery-grade iron phosphate and battery-grade iron oxide red includes the following steps: Step 1: Mix sulfuric acid and phosphoric acid in a molar ratio of 0.6-1.2:1 to obtain a phosphorus-containing mixed acid. Add a zero-valent iron source. The molar amount of phosphoric acid in the phosphorus-containing mixed acid is 70% to 95% of the theoretical molar amount of phosphoric acid required to completely convert the zero-valent iron source into ferric phosphate. After the zero-valent iron source dissolves, oxygen is introduced into the reaction system to carry out an oxidation reaction until the phosphate concentration is ≤0.05 g / L. Then, the solid and liquid are separated to obtain ferric phosphate filter cake and mother liquor A containing ferrous ions. Step 2: Concentrate the mother liquor A to increase the ferrous ion concentration to 30-60 g / L, obtaining concentrated mother liquor A. Pre-oxidize the concentrated mother liquor A by introducing ozone at 20-60 °C for 15-30 minutes, controlling the ozone dosage to be 0.9-1.5 times the molar amount of ferrous ions in the concentrated mother liquor A. Add 0.5%-5% (by mass) of α-Fe₂O₃ seed crystals from the concentrated mother liquor A, and perform a hydrolysis reaction at 130-160 °C under sealed conditions for 4-8 hours. Separate the solid and liquid phases to obtain crude iron oxide red and mother liquor B. Step 3: Wash, dry, and calcine the ferric phosphate filter cake obtained in Step 1 to obtain battery-grade ferric phosphate; wash, dry, and calcine the crude iron oxide red obtained in Step 2 to obtain battery-grade iron oxide red; concentrate the mother liquor B and return it to Step 1 for the preparation of phosphorus-containing mixed acid.
[0007] Preferably, the zero-valent iron source in step 1 is iron powder, iron filings, or iron sheet with a purity greater than 99.0%.
[0008] Preferably, the oxygen flow rate in step 1 is 1~3 m³ / h. 3 / h, the oxidation reaction is carried out at a temperature of 25~50 ℃.
[0009] Preferably, the concentration in step 2 is low-temperature evaporation concentration or membrane concentration.
[0010] Preferably, the heating rate in step 2 is 2~5 °C / min.
[0011] Preferably, step 3 is as follows: the ferric phosphate filter cake obtained in step 1 is washed with water, dried, and calcined at 550 ℃~750 ℃ for 2~6 hours to obtain battery-grade ferric phosphate; the crude iron oxide red obtained in step 2 is acid-washed, washed with water, dried, and calcined at 600 ℃~650 ℃ for 1~4 hours to obtain battery-grade iron oxide red; the mother liquor B is concentrated to make the sulfuric acid mass concentration 50%~70% and returned to step 1 for the preparation of phosphorus-containing mixed acid.
[0012] The present invention has the following beneficial effects: 1. Achieve efficient and graded utilization of iron and flexible control of co-production ratio. By controlling the amount of phosphoric acid used to 70%-95% of the theoretical amount, the graded distribution of iron between ferric phosphate and iron oxide red can be achieved, and the co-production ratio can be flexibly adjusted, with a total iron utilization rate of ≥98%.
[0013] 2. Construct a low-energy-consumption, high-quality iron oxide red preparation route. Concentrate the mother liquor to an iron concentration of 30-60 g / L, which reduces hydrolysis energy consumption and provides high supersaturation, generating high-purity nano-iron oxide red with uniform particle size (D50 50~100 nm) under seed induction.
[0014] 3. A step-by-step oxidation strategy ensures both product quality and process economy. The first step uses oxygen oxidation, which is low-cost; the second step uses ozone pre-oxidation to completely convert ferrous ions into ferric ions, avoiding the formation of impurity phases and ensuring that the iron oxide meets battery-grade standards.
[0015] 4. Achieve closed-loop circulation and clean production of the reaction medium. Mother liquor B (dilute sulfuric acid) is concentrated and returned to step 1 for recycling, reducing the amount of fresh sulfuric acid used and waste liquid discharge. The recycling process is stable and the product quality is reliable.
[0016] 5. This invention overcomes the problems of long process flow, low raw material utilization, and large waste discharge caused by the separate preparation of iron phosphate and iron oxide red in the prior art, as well as the problems of high energy consumption, low yield, and difficulty in particle size control in the production of iron oxide red due to the low iron concentration of the mother liquor in the existing co-production process. This invention achieves a balance in the yield of the two products, optimizes energy consumption, and can stably co-produce battery-grade iron phosphate and battery-grade iron oxide red. It realizes the co-production of two high-value-added battery materials, iron phosphate and iron oxide red, as well as the internal circulation of the reaction medium. It is an integrated method with high resource utilization, excellent product quality, high purity, and environmental friendliness. Attached Figure Description
[0017] Figure 1 SEM image of the battery-grade iron phosphate prepared in Example 1.
[0018] Figure 2 SEM image of battery-grade iron oxide red prepared in Example 1. Detailed Implementation
[0019] The raw materials used in the embodiments of this invention are all commercially available industrial-grade products: iron filings (iron content ≥99.0%, particle size 20~100 mesh), iron powder (iron content ≥99.0%, particle size 20~100 mesh), iron scale (iron content ≥99.0%, processed into 20~100 mesh particles), phosphoric acid (industrial grade, 85%), sulfuric acid (industrial grade, 98%), ozone (self-made, concentration 50 mg / L), and α-Fe2O3 seed crystals (self-made or commercially available).
[0020] The battery-grade iron phosphate refers to a product with an Fe / P molar ratio of 0.97~1.02 and a D50 particle size between 2~5 μm (based on relevant data indicators in specifications such as HG / T4701-2021 and YS / T 1027-2024); the battery-grade iron oxide red refers to a product with an Fe2O3 content ≥99.0% and a D50 particle size between 50~100 nm.
[0021] Explanation regarding production adjustment: The method of this invention allows for flexible adjustment of the yield ratio of ferric phosphate and iron oxide red according to market demand. When the amount of phosphoric acid is close to the theoretical upper limit (95%), the yield of ferric phosphate increases, and the yield of iron oxide red decreases accordingly; when the amount of phosphoric acid is close to the theoretical lower limit (70%), the yield of iron oxide red increases, and the yield of ferric phosphate decreases accordingly. Examples 1 and 2 demonstrate the yield adjustment capability.
[0022] Example 1 A method for co-producing battery-grade iron phosphate and battery-grade iron oxide red includes the following steps: Step 1: Mix sulfuric acid and phosphoric acid in a molar ratio of 0.6:1 to obtain a phosphorus-containing mixed acid. Adjust the temperature to 25°C and add a zero-valent iron source (iron content = 99.1% iron filings). The molar amount of phosphoric acid in the phosphorus-containing mixed acid is 70% of the theoretical molar amount of phosphoric acid required to completely convert the zero-valent iron source into ferric phosphate. After the iron filings dissolve, oxygen is introduced into the reaction system (oxygen flow rate is 1 m³ / min). 3 The reaction was carried out at 25℃, and the phosphate concentration was monitored during the reaction. The reaction was stopped when the phosphate concentration reached 0.04 g / L. Solid-liquid separation was performed to obtain ferric phosphate filter cake and mother liquor A containing ferrous ions (iron concentration 28.5 g / L). Step 2: The mother liquor A is concentrated by low-temperature evaporation (60℃) to increase the ferrous ion concentration in the mother liquor A to 60 g / L, resulting in concentrated mother liquor A. Ozone is then introduced at 20℃ for pre-oxidation treatment for 30 minutes, with the ozone dosage controlled to be 0.9 times the molar amount of ferrous ions in the concentrated mother liquor A. 3% (by mass) of α-Fe₂O₃ seed crystals from the concentrated mother liquor A are added, and the mixture is heated to 145℃ at a rate of 3.5℃ / min under sealed conditions for hydrolysis reaction for 6 hours. Solid-liquid separation yields crude iron oxide red and mother liquor B. Step 3: Wash the ferric phosphate filter cake obtained in Step 1 with water three times, dry it at 120℃ for 4 hours, and calcine it at 550℃ for 6 hours to obtain battery-grade ferric phosphate (see...). Figure 1 The crude iron oxide red obtained in step 2 was acid-washed with 5% dilute sulfuric acid (mass concentration) at room temperature for 0.5 hours, washed with deionized water until neutral, dried at 120℃ for 4 hours, and calcined at 600℃ for 4 hours to obtain battery-grade iron oxide red (see...). Figure 2 After concentrating the mother liquor B to achieve a sulfuric acid concentration of 50%, return it to step 1 to prepare a phosphorus-containing mixed acid.
[0023] Product performance test results: Battery-grade iron phosphate: Fe / P molar ratio 0.97, D50 particle size 2.8 μm.
[0024] Battery-grade iron oxide red: Fe2O3 content 99.3%, D50 particle size 65 nm.
[0025] Example 2 A method for co-producing battery-grade iron phosphate and battery-grade iron oxide red includes the following steps: Step 1: Mix sulfuric acid and phosphoric acid in a molar ratio of 1.2:1 to obtain a phosphorus-containing mixed acid. Adjust the temperature to 50°C and add a zero-valent iron source (iron content = 99.0% iron powder). The molar amount of phosphoric acid in the phosphorus-containing mixed acid is 95% of the theoretical molar amount of phosphoric acid required to completely convert the zero-valent iron source into ferric phosphate. After the iron powder dissolves, oxygen is introduced into the reaction system (oxygen flow rate is 3 m³ / s). 3 The reaction was carried out at 50℃ for 6 hours. The phosphate concentration was monitored during the reaction and stopped when the phosphate concentration reached 0.02 g / L. Solid-liquid separation was performed to obtain ferric phosphate filter cake and mother liquor A containing ferrous ions (iron concentration 8.2 g / L). Step 2: The mother liquor A is concentrated using a membrane to increase the ferrous ion concentration in the mother liquor A to 30 g / L, resulting in concentrated mother liquor A. This is then pre-oxidized by introducing ozone at 60°C for 15 minutes, with the ozone dosage controlled to be 1.5 times the molar amount of ferrous ions in the concentrated mother liquor A. 5% (by mass) of α-Fe₂O₃ seed crystals from the concentrated mother liquor A are added, and the mixture is heated to 130°C at a rate of 5°C / min under sealed conditions for hydrolysis for 8 hours. Solid-liquid separation yields crude iron oxide red and mother liquor B. Step 3: Wash the ferric phosphate filter cake obtained in Step 1 with water 3 times, dry it at 120℃ for 4 hours, and calcine it at 750℃ for 2 hours to obtain battery-grade ferric phosphate; wash the crude iron oxide red obtained in Step 2 with 5% dilute sulfuric acid (mass concentration) at room temperature for 2 hours, wash it with deionized water until neutral, dry it at 120℃ for 4 hours, and calcine it at 650℃ for 1 hour to obtain battery-grade iron oxide red; concentrate the mother liquor B to make the sulfuric acid mass concentration 60% and return it to Step 1 for the preparation of phosphorus-containing mixed acid.
[0026] Product performance test results: Battery-grade iron phosphate: Fe / P molar ratio 0.99, D50 particle size 4.5 μm.
[0027] Battery-grade iron oxide red: Fe2O3 content 99.5%, D50 particle size 55 nm.
[0028] Example 3 A method for co-producing battery-grade iron phosphate and battery-grade iron oxide red includes the following steps: Step 1: Mix sulfuric acid and phosphoric acid in a molar ratio of 0.9:1 to obtain a phosphorus-containing mixed acid. Adjust the temperature to 40°C and add a zero-valent iron source (iron content = 99.05% iron scrap). The molar amount of phosphoric acid in the phosphorus-containing mixed acid is 85% of the theoretical molar amount of phosphoric acid required to completely convert the zero-valent iron source into ferric phosphate. After the iron scrap dissolves, oxygen is introduced into the reaction system (oxygen flow rate is 2m³ / min). 3 The reaction was carried out at 40℃, and the phosphate concentration was monitored during the reaction. The reaction was stopped when the phosphate concentration reached 0.05 g / L. The solid and liquid were separated to obtain ferric phosphate filter cake and mother liquor A containing ferrous ions (iron concentration 18.5 g / L).
[0029] Step 2: The mother liquor A is concentrated using a membrane to increase the ferrous ion concentration in the mother liquor A to 50 g / L, resulting in concentrated mother liquor A. This is then pre-oxidized by introducing ozone at 35°C for 25 minutes, with the ozone dosage controlled to be 1.2 times the molar amount of ferrous ions in the concentrated mother liquor A. 0.5% (by mass) of α-Fe₂O₃ seed crystals from the concentrated mother liquor A are added, and the mixture is heated to 160°C at a rate of 2°C / min under sealed conditions for a hydrolysis reaction for 4 hours. Solid-liquid separation yields crude iron oxide red and mother liquor B. Step 3: Wash the ferric phosphate filter cake obtained in Step 1 with water 3 times, dry it at 120℃ for 4 hours, and calcine it at 650℃ for 4 hours to obtain battery-grade ferric phosphate; wash the crude iron oxide red obtained in Step 2 with 5% dilute sulfuric acid (mass concentration) at room temperature for 2 hours, wash it with deionized water until neutral, dry it at 120℃ for 4 hours, and calcine it at 620℃ for 3 hours to obtain battery-grade iron oxide red; concentrate the mother liquor B to make the sulfuric acid mass concentration 70% and return it to Step 1 for the preparation of phosphorus-containing mixed acid.
[0030] Product performance test results: Battery-grade iron phosphate: Fe / P molar ratio 0.98, D50 particle size 3.2 μm.
[0031] Battery-grade iron oxide red: Fe2O3 content 99.6%, D50 particle size 89 nm.
[0032] Example 4 This embodiment is used to illustrate the stability of the mother liquor B recycling process in the method of the present invention.
[0033] Five consecutive batches of cyclic experiments were conducted according to the method in Example 3. Starting from the second batch, the sulfuric acid used to prepare the phosphorus-containing mixed acid in step 1 was provided by a combination of fresh concentrated sulfuric acid and the concentrated mother liquor B from the previous batch in step 3. The amounts of both were adjusted by calculation to ensure that the initial total amount and molar ratio of sulfuric acid in the reaction system remained consistent with those in the first batch.
[0034] The iron concentrations of mother liquor A obtained in step 1 for each batch before concentration were 18.5 g / L (batch 1), 18.3 g / L (batch 2), 18.7 g / L (batch 3), 18.4 g / L (batch 4), and 18.6 g / L (batch 5), respectively. The test results of the products obtained in step 3 for each batch are as follows:
[0035] The results showed that after five consecutive batches of recycling, the iron concentration in mother liquor A remained stable, and the key indicators of iron phosphate and iron oxide red products did not change significantly, remaining within the range of battery-grade products. The mother liquor B recycling process of this invention exhibits good stability.
[0036] Comparative Example 1 Follow steps 1 and 3 of Example 1, but ozone pre-oxidation is omitted in step 2; instead, air is introduced (flow rate 2 m³ / s). 3 / (m 3 •h)) was oxidized under the same conditions, with other conditions the same as in Example 1.
[0037] The obtained iron oxide red product had a Fe2O3 content of 98.3%, a D50 particle size of 0.82 μm (820 nm), a wide particle size distribution, and the presence of large particles. The product failed to meet battery-grade requirements, mainly due to incomplete oxidation of ferrous ions, which led to the formation of impurity phases during hydrolysis.
[0038] Comparative Example 2 Follow steps 1 and 3 of Example 1, but do not add α-Fe2O3 seeds in step 2, and directly carry out the hydrolysis reaction, with other conditions the same as in Example 1.
[0039] The obtained iron oxide red product had a Fe2O3 content of 98.6%, a D50 particle size of 1.1 μm (1100 nm), a wide particle size distribution, and an irregular morphology. The product failed to meet battery-grade requirements, indicating that seed crystals are crucial for controlling particle size and morphology.
[0040] Comparative Example 3 The process was followed according to Example 1, but the molar amount of phosphoric acid in the phosphoric acid mixture in step 1 was adjusted to 105% of the theoretical amount (excess phosphoric acid), and other conditions were the same as in Example 1.
[0041] Residual phosphoric acid (phosphate concentration 0.35 g / L) was found in mother liquor A after step 1 reaction. The iron oxide red product obtained after the hydrolysis reaction in step 2 had an Fe2O3 content of 96.8% (phosphate contamination) and a D50 particle size of 1.4 μm (1400 nm). The product failed to meet battery-grade requirements, indicating that excessive phosphoric acid contaminates the iron oxide red product.
[0042] Comparative Example 4 The process is the same as in Example 3, but step 2 does not involve concentrating mother liquor A; instead, ozone oxidation and hydrolysis are performed directly (the iron concentration of mother liquor A is 18.5 g / L).
[0043] Results: Processing 5 L of low-concentration mother liquor A required scaling up the reactor volume, and the heating energy consumption was 4.2 times that of Example 3. Although the purity of the subsequent iron oxide red product could still reach 99.3% and the D50 particle size was 0.27 μm, the energy consumption per unit product increased significantly, resulting in decreased economic efficiency.
Claims
1. A method for co-producing battery-grade iron phosphate and battery-grade iron oxide red, characterized in that, Includes the following steps: Step 1: Mix sulfuric acid and phosphoric acid in a molar ratio of 0.6-1.2:1 to obtain a phosphorus-containing mixed acid. Add a zero-valent iron source. The molar amount of phosphoric acid in the phosphorus-containing mixed acid is 70% to 95% of the theoretical molar amount of phosphoric acid required to completely convert the zero-valent iron source into ferric phosphate. After the zero-valent iron source dissolves, oxygen is introduced into the reaction system to carry out an oxidation reaction until the phosphate concentration is ≤0.05 g / L. Then, the solid and liquid are separated to obtain ferric phosphate filter cake and mother liquor A containing ferrous ions. Step 2: Concentrate the mother liquor A to increase the ferrous ion concentration to 30-60 g / L, obtaining concentrated mother liquor A. Pre-oxidize the concentrated mother liquor A by introducing ozone at 20-60 °C for 15-30 minutes, controlling the ozone dosage to be 0.9-1.5 times the molar amount of ferrous ions in the concentrated mother liquor A. Add 0.5%-5% (by mass) of α-Fe₂O₃ seed crystals from the concentrated mother liquor A, and perform a hydrolysis reaction at 130-160 °C under sealed conditions for 4-8 hours. Separate the solid and liquid phases to obtain crude iron oxide red and mother liquor B. Step 3: Wash, dry, and calcine the ferric phosphate filter cake obtained in Step 1 to obtain battery-grade ferric phosphate; wash, dry, and calcine the crude iron oxide red obtained in Step 2 to obtain battery-grade iron oxide red; concentrate the mother liquor B and return it to Step 1 for the preparation of phosphorus-containing mixed acid.
2. The method according to claim 1, characterized in that... The zero-valent iron source mentioned in step 1 is iron powder, iron filings, or iron sheet with a purity greater than 99.0%.
3. The method according to claim 1, characterized in that... In step 1, the oxygen flow rate is 1~3 m³ / h. 3 / h, the oxidation reaction is carried out at a temperature of 25~50 ℃.
4. The method according to claim 1, characterized in that... The concentration described in step 2 is either low-temperature evaporation concentration or membrane concentration.
5. The method according to claim 1, characterized in that... The heating rate in step 2 is 2~5 °C / min.
6. The method according to claim 1, characterized in that... Step 3 is as follows: The ferric phosphate filter cake obtained in Step 1 is washed with water, dried, and calcined at 550 ℃~750 ℃ for 2~6 hours to obtain battery-grade ferric phosphate; the crude iron oxide red obtained in Step 2 is acid-washed, washed with water, dried, and calcined at 600 ℃~650 ℃ for 1~4 hours to obtain battery-grade iron oxide red; the mother liquor B is concentrated to make the sulfuric acid mass concentration 50%~70% and returned to Step 1 for the preparation of phosphorus-containing mixed acid.