Method for preparing lithium iron phosphate by using zinc-zincite slag by wet process

Abstract

The application discloses a method for preparing lithium iron phosphate by using zinc hydrometallurgy hematite slag, and belongs to the technical field of hydrometallurgy. 3+ The hematite slag is mixed with an acid leaching agent to obtain mixed slurry a, sulfur dioxide is introduced for pressure reduction leaching, and solid-liquid separation is performed to obtain ferrous sulfate leaching liquor with a concentration of less than 1 g / L. The ferrous sulfate leaching liquor is mixed with a reducing agent, a phosphorus source and a lithium source to obtain mixed ore slurry b, and after high-temperature hydrothermal treatment, solid-liquid separation, washing and drying, the target lithium iron phosphate is obtained. The method directly uses the zinc hydrometallurgy hematite slag as the iron source of the lithium iron phosphate, and the two-stage process adopted is connected in a closed reaction condition and process parameters, and no three-waste emissions are formed, thus forming an overall synergistic effect which is not possessed by the existing process. The process is short, the operation is fully wet, the environment is friendly, and high-value resource utilization of the zinc hydrometallurgy hematite slag is realized.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgical technology, specifically relating to a method for preparing lithium iron phosphate using hematite slag from hydrometallurgical zinc smelting. Background Technology

[0002] Zinc-iron separation is a core and critical issue in hydrometallurgical zinc refining. Currently, the main industrial methods for zinc-iron separation are the jaundice process, the goethite process, and the hematite process, all of which are widely used in the hydrometallurgical zinc refining industry. Among these, the iron slag produced by the hematite process is the crystalline compound α-Fe₂O₃, which has significant advantages such as good stability, excellent filtration performance, high iron content (high Fe content, low Zn content), and small slag volume. It can be sold as a raw material for industries such as cement production, iron smelting, and pigment preparation, thus realizing the resource utilization of iron slag.

[0003] However, currently, the iron slag from hydrometallurgical zinc smelting is mainly sold at low prices as a raw material in traditional fields such as cement, iron smelting, and pigments, resulting in low added value and limited economic benefits. Meanwhile, existing lithium iron phosphate production routes generally suffer from high raw material costs, complex processes, and environmental unfriendliness, hindering their large-scale application.

[0004] Based on the growing market demand for lithium iron phosphate and the application potential of α-Fe2O3 in the materials field, this invention proposes a method for preparing lithium iron phosphate using hematite slag from hydrometallurgical zinc smelting, aiming to achieve high-value utilization of hematite slag from hydrometallurgical zinc smelting. This method utilizes widely available and inexpensive raw materials, and generates no waste gas, wastewater, or waste residue during the preparation process, demonstrating significant environmental friendliness and economic benefits. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing lithium iron phosphate using hematite slag from a wet zinc smelting process.

[0006] The objective of this invention is achieved as follows: the method for preparing lithium iron phosphate using hematite slag from a wet zinc smelting process includes the following steps: Pressure reduction leaching: Hematite slag is mixed with an acidic leaching agent to obtain mixed slurry a. Sulfur dioxide is then introduced for pressure reduction leaching, and solid-liquid separation yields Fe. 3+ Ferrous sulfate leachate with a concentration <1g / L; High-temperature hydrothermal synthesis: Ferrous sulfate leachate is mixed with reducing agent, phosphorus source and lithium source to obtain mixed slurry b. After high-temperature hydrothermal treatment, solid-liquid separation, washing and drying are performed to obtain the target lithium iron phosphate.

[0007] Compared with the prior art, the technical solution described in this invention has the following advantages: This technical solution utilizes pressure reduction leaching to convert iron in hematite slag into Fe.3+ Form leaching and in-situ reduction to Fe 2+ This process simultaneously achieves effective separation of impurities such as iron and zinc. The ferrous sulfate leachate (Fe...) produced by the pressure reduction leaching process... 3+ With a concentration of <1g / L, it can be directly used as an iron source for hydrothermal synthesis without additional purification treatment, realizing the high-value utilization of iron removal slag from wet zinc smelting.

[0008] This technical solution can directly convert hematite slag from wet zinc smelting into the target lithium iron phosphate through two processes: pressurized leaching and hydrothermal synthesis under closed conditions. The two processes form an overall synergistic effect that is not found in existing processes in terms of closed reaction conditions, matching and connection of process parameters, no emissions of waste gas, wastewater, and solid waste, and environmental friendliness.

[0009] In summary, this technical solution features a short process flow, fully wet operation, and environmental friendliness, achieving high-value-added resource utilization of hematite slag from wet zinc smelting, and is of great value for promotion and application. Attached Figure Description

[0010] Figure 1 This is a process flow diagram of the technical solution described in this invention; Figure 2 These are the XRD patterns of lithium iron phosphate prepared in Examples 1, 2 and 3. Detailed Implementation

[0011] The present invention will be further described below, but this is not intended to limit the invention in any way. Any modifications or substitutions made based on the teachings of the present invention shall fall within the scope of protection of the present invention.

[0012] The method for preparing lithium iron phosphate using hematite slag from wet zinc smelting according to the present invention includes the following steps: Pressure reduction leaching: Hematite slag is mixed with an acidic leaching agent to obtain mixed slurry a. Sulfur dioxide is then introduced for pressure reduction leaching, and solid-liquid separation yields Fe. 3+ Ferrous sulfate leachate with a concentration <1g / L; High-temperature hydrothermal synthesis: Ferrous sulfate leachate is mixed with reducing agent, phosphorus source and lithium source to obtain mixed slurry b. After high-temperature hydrothermal treatment, solid-liquid separation, washing and drying are performed to obtain the target lithium iron phosphate.

[0013] The slag from the wet zinc smelting hematite process is the iron removal slag from the wet zinc smelting hematite process.

[0014] In the pressure reduction leaching process, the acidic leaching agent is preferably sulfuric acid. Based on the total iron content of the hematite slag, the excess coefficient of sulfuric acid is 1.2~1.5, and the solid-liquid ratio is 1:5~8 g / mL.

[0015] In the pressure reduction leaching process, sulfur dioxide is introduced to maintain the partial pressure of sulfur dioxide in the reaction system at 0.15~0.3MPa, and pressure reduction leaching is carried out under closed conditions.

[0016] The pressure reduction leaching is carried out at a temperature of 80~120℃ for a time of 0.5~2.0h.

[0017] In the high-temperature hydrothermal synthesis process, the reducing agent is preferably ascorbic acid, used in an amount of 0.002~0.005 g / ml. The phosphorus source is preferably phosphoric acid with a concentration of 12~16 mol / L, based on the Fe content in the ferrous sulfate solution. 2+ The excess coefficient of phosphoric acid is 1.2~1.5. The preferred lithium source is lithium hydroxide, based on the Fe content in the ferrous sulfate solution. 2+ The excess coefficient of lithium hydroxide is 1.1~1.2.

[0018] The high-temperature hydrothermal synthesis is carried out at a temperature of 180~220℃ for 8~10 hours.

[0019] Both the pressurized reduction leaching process and the high-temperature hydrothermal synthesis process are carried out under closed conditions.

[0020] Example 1

[0021] Raw materials: Hematite slag provided by a hydrometallurgical zinc smelting enterprise was used as raw material. The main components (wt%) were: Fe 59.17%, Zn 0.27%, S 2.68%, SiO2 0.21%, As 0.14%, K 0.10%, Na 0.070%, etc.

[0022] Pressure reduction leaching: 150g of hematite slag and 1200mL of 155g / L sulfuric acid were placed in a 2L high-pressure reactor to obtain a mixed slurry a. Sulfur dioxide gas was introduced to maintain the partial pressure of sulfur dioxide in the reaction system at 0.15~0.3 MPa. Pressure reduction leaching was carried out at 80~120 (80)℃ for 0.5~2.0 (2.0) h. Solid-liquid separation was performed to obtain Fe. 3+ Ferrous sulfate leachate with a concentration of 0.3 g / L.

[0023] High-temperature hydrothermal synthesis: 648 mL of ferrous sulfate leaching solution, 2.6 g of ascorbic acid, 159 mL of 15 mol / L phosphoric acid and 477 mL of 2 mol / L lithium hydroxide were placed in a 2 L autoclave to obtain mixed slurry b. After hydrothermal treatment at 180~220 (180) °C for 8~10 (10) h, solid-liquid separation was performed. The solid product was washed multiple times with deionized water and anhydrous ethanol, and then vacuum dried at 70 °C for 12 h. Finally, it was ground to obtain the target lithium iron phosphate.

[0024] The lithium iron phosphate obtained in Example 1 was characterized by XRD, and the results are as follows: Figure 2 As shown.

[0025] Example 2

[0026] Pressure reduction leaching: 200g of hematite slag and 1200mL of 225g / L sulfuric acid were placed in a 2L high-pressure reactor to obtain a mixed slurry a. Sulfur dioxide gas was introduced to maintain the partial pressure of sulfur dioxide in the reaction system at 0.15~0.3 MPa. Pressure reduction leaching was carried out at 80~120 (90)℃ for 0.5~2.0 (1.0) h. Solid-liquid separation was performed to obtain Fe. 3+ Ferrous sulfate leachate with a concentration of 0.2 g / L.

[0027] High-temperature hydrothermal synthesis: 665 mL of ferrous sulfate leaching solution, 3.9 g of ascorbic acid, 184 mL of 15 mol / L phosphoric acid and 609 mL of 2 mol / L lithium hydroxide were placed in a 2 L autoclave to obtain mixed slurry b. After hydrothermal treatment at 180~220 (200) °C for 8~10 (9) h, solid-liquid separation was performed. The solid product was washed multiple times with deionized water and anhydrous ethanol, and then vacuum dried at 70 °C for 12 h. Finally, it was ground to obtain the target lithium iron phosphate.

[0028] The lithium iron phosphate obtained in Example 2 was characterized by XRD, and the results are as follows: Figure 2 As shown.

[0029] Example 3

[0030] Pressure reduction leaching: 300g of hematite slag and 1500mL of 315g / L sulfuric acid were placed in a 2L high-pressure reactor to obtain mixed slurry a. Sulfur dioxide gas was introduced to maintain the partial pressure of sulfur dioxide in the reaction system at 0.15~0.3 MPa. Pressure reduction leaching was carried out at 80~120 (120)℃ for 0.5~2.0 (0.5) h. Solid-liquid separation was performed to obtain Fe. 3+ Ferrous sulfate leachate with a concentration of 0.4 g / L.

[0031] High-temperature hydrothermal synthesis: 840 mL of ferrous sulfate leaching solution, 8.4 g of ascorbic acid, 255 mL of 15 mol / L phosphoric acid and 874 mL of 2 mol / L lithium hydroxide were placed in a 2 L autoclave to obtain mixed slurry b. After hydrothermal treatment at 180~220 (220) °C for 8~10 (8) h, solid-liquid separation was performed. The solid product was washed multiple times with deionized water and anhydrous ethanol, and then vacuum dried at 70 °C for 12 h. Finally, it was ground to obtain the target lithium iron phosphate.

[0032] The lithium iron phosphate obtained in Example 3 was characterized by XRD, and the results are as follows: Figure 2 As shown.

[0033] Figure 2The XRD patterns of lithium iron phosphate prepared in Examples 1, 2, and 3 are shown. The results indicate that the XRD pattern of lithium iron phosphate prepared in Example 1 is basically consistent with the LiFePO4 standard card (PDF#40-1499), showing only LiFePO4 diffraction peaks without other impurities, and the peaks are sharp, indicating that the LiFePO4 crystal has high crystallinity. The XRD pattern of lithium iron phosphate prepared in Example 2 also shows only LiFePO4 diffraction peaks without other impurities, and the peaks are sharp. Compared with the results of Example 1, the diffraction peaks of the two are basically consistent, further verifying the repeatability and stability of the preparation process of this invention. The XRD pattern of lithium iron phosphate prepared in Example 3 also shows only LiFePO4 diffraction peaks without other impurities, and the peaks are sharp. Compared with the results of Examples 1 and 2, the diffraction peaks are basically consistent, again verifying the repeatability and stability of the preparation process of this invention.

Claims

1. A method for preparing lithium iron phosphate using hematite slag from a wet zinc smelting process, characterized in that, The process includes the following steps: Pressure reduction leaching: Hematite slag is mixed with an acidic leaching agent to obtain mixed slurry a. Sulfur dioxide is then introduced for pressure reduction leaching, and solid-liquid separation yields Fe. 3+ Ferrous sulfate leachate with a concentration <1g / L; High-temperature hydrothermal synthesis: Ferrous sulfate leachate is mixed with reducing agent, phosphorus source and lithium source to obtain mixed slurry b. After high-temperature hydrothermal treatment, solid-liquid separation, washing and drying are performed to obtain the target lithium iron phosphate.

2. The method for preparing lithium iron phosphate using hematite slag from wet zinc smelting according to claim 1, characterized in that, In the pressure reduction leaching process, the acidic leaching agent is sulfuric acid. Based on the total iron content of the hematite slag, the excess coefficient of sulfuric acid is 1.2~1.5, and the solid-liquid ratio is 1:5~8 g / mL.

3. The method for preparing lithium iron phosphate using hematite slag from wet zinc smelting according to claim 1, characterized in that, In the pressure reduction leaching process, sulfur dioxide is introduced to maintain the partial pressure of sulfur dioxide in the reaction system at 0.15~0.3 MPa, and pressure reduction leaching is carried out under closed conditions.

4. The method for preparing lithium iron phosphate using hematite slag from wet zinc smelting according to claim 1, characterized in that, The pressure reduction leaching is carried out at a temperature of 80~120℃ for a time of 0.5~2.0h.

5. The method for preparing lithium iron phosphate using hematite slag from wet zinc smelting according to claim 1, characterized in that, In the high-temperature hydrothermal synthesis process, the reducing agent is ascorbic acid, and the dosage is 0.002~0.005g / ml.

6. The method for preparing lithium iron phosphate using hematite slag from wet zinc smelting according to claim 1, characterized in that, In the high-temperature hydrothermal synthesis process, the phosphorus source is phosphoric acid with a concentration of 12-16 mol / L, based on the Fe in the ferrous sulfate solution. 2+ The excess coefficient of phosphoric acid is 1.2~1.

5.

7. The method for preparing lithium iron phosphate using hematite slag from wet zinc smelting according to claim 1, characterized in that, In the high-temperature hydrothermal synthesis process, the lithium source is lithium hydroxide, based on the Fe in the ferrous sulfate solution. 2+ The excess coefficient of lithium hydroxide is 1.1~1.

2.

8. The method for preparing lithium iron phosphate using hematite slag from wet zinc smelting according to claim 1, characterized in that, The high-temperature hydrothermal synthesis is carried out at a temperature of 180~220℃ for 8~10 hours.

9. The method for preparing lithium iron phosphate using hematite slag from wet zinc smelting according to claim 1, characterized in that, The high-temperature hydrothermal synthesis is carried out under closed conditions.

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