Method for removing iron from zinc hydrometallurgy phosphate and co-producing battery-grade iron phosphate

Abstract

The invention discloses a method for removing iron from zinc hydrometallurgy phosphate and co-producing battery-grade iron phosphate. The method comprises the following steps: (1) crushing and grading zinc concentrate, and oxidizing and roasting; (2) adding dilute sulphuric acid or waste electrolyte and an oxidizing agent, oxidizing and leaching to obtain a neutral leachate, standing and thickening, and carrying out solid-liquid separation to obtain a neutral underflow solid phase and neutral supernate; (3) dilute acid is added into the neutral underflow solid phase for hot acid leaching, solid-liquid separation is conducted, and leaching residues and leaching liquid are obtained; (4) adding a phosphorus source into the leachate, adjusting the pH value, and coprecipitating to prepare iron phosphate; and (5) filtering and washing the iron phosphate obtained by coprecipitation, and carrying out heat treatment crystallization to obtain the battery-grade iron phosphate. According to the method, the iron removal link in the zinc hydrometallurgy process is combined with the preparation process of the battery-grade iron phosphate, and iron slag source emission reduction and green and clean production in the zinc smelting process are achieved; the acid waste liquid generated in the coprecipitation process is circularly used for zinc smelting neutral leaching, sulfuric acid consumption is reduced, and waste liquid discharge is reduced.

Description

Technical Field

[0001] The present invention relates to a method for preparing battery-grade ferric phosphate, in particular to a method for preparing battery-grade ferric phosphate by coupling hydrometallurgical zinc removal with phosphate removal, and belongs to the technical field of hydrometallurgy. Background Art

[0002] Over 85% of the world's zinc is produced through hydrometallurgy. This involves roasting and leaching zinc ore to extract the zinc into a leachate, which is then electrolyzed to produce elemental zinc. However, zinc ore contains significant amounts of iron impurities, which can enter the leachate during the leaching process, affecting the effectiveness of subsequent electrolytic refining. To address this issue, a purification process is often added before electrolysis, focusing on converting the iron into a precipitate for separation. By 2023, China's refined zinc production had reached 7 million tons, ranking first globally. This massive zinc output inevitably generates a significant amount of iron-containing waste slag. Finding suitable methods to recycle this iron resource is of great practical value.

[0003] With the continued advancement of the new energy sector, the power battery industry has experienced rapid growth. Lithium-ion batteries, with their superior performance and low production costs, have become a major trend in the industry. Lithium iron phosphate batteries, characterized by a stable charge and discharge platform, excellent safety performance, and low cost, are widely used in new energy vehicles, energy storage devices, and other fields. Currently, one of the mainstream synthesis processes for lithium iron phosphate is the iron phosphate process, which uses iron phosphate as a precursor, wet-grinding and mixing it with a lithium source and a carbon source, and then using a carbothermal reduction method to prepare the lithium iron phosphate cathode material. In this preparation method, the properties of the iron phosphate precursor essentially determine the overall performance of the lithium iron phosphate material.

[0004] After years of exploration, zinc smelting has developed a variety of mature iron removal processes. However, the removed iron still needs to be recycled to avoid environmental pollution and waste of resources. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the deficiency in the prior art that iron resources are difficult to be recycled in the wet zinc smelting production process. A method for removing iron from phosphate in wet zinc smelting and co-producing battery-grade iron phosphate is proposed. The wet zinc smelting is combined with the co-precipitation process for preparing iron phosphate, and battery-grade iron phosphate is prepared by utilizing the iron resources in zinc ore. At the same time, the waste liquid generated by the co-precipitation is used to circulate and leach the roasted ore.

[0006] The present invention not only realizes high-quality utilization of iron resources in zinc ore, but also realizes recycling of waste liquid in the process of preparing ferric phosphate by coprecipitation.

[0007] The technical solution adopted by the present invention to solve the technical problem is a method for removing iron from zinc phosphate by wet smelting and co-producing battery-grade iron phosphate, comprising the following steps:

[0008] (1) crushing and classifying the zinc concentrate, and oxidizing and roasting it to obtain roasted ore;

[0009] (2) adding dilute sulfuric acid or spent electrolyte to the roasted ore obtained in step (1), adding an oxidant, controlling the pH of the system, oxidizing and leaching to obtain a neutral leachate, and allowing the leachate to stand and concentrate, and performing solid-liquid separation to obtain a neutral underflow solid phase and a neutral supernatant;

[0010] The final pH after leaching is close to neutral, so it is called neutral leaching. Because the main components of roasted ore are zinc oxide and iron oxide, the addition of dilute sulfuric acid converts these oxides into ions. The amount of oxidant used is mainly determined by the ferrous content in the roasted ore. The main reactions that occur in roasted ore leaching are as follows:

[0011] ZnO+H2SO4=ZnSO4+H2O (1)

[0012] 2FeSO4+MnO2+2H2SO4=Fe2(SO4)3+MnSO4+2H2O (2)

[0013] Fe2(SO4)3+6H2O=2Fe(OH)3↓+3H2SO4 (3)

[0014] Therefore, the amount of sulfuric acid is determined by precise control of pH. The oxidant is mainly used to oxidize the ferrous ions in the roasted ore into ferric iron. Therefore, the amount of oxidant used should be sufficient to oxidize all the ferrous ions in the roasted ore.

[0015] Neutral concentration in hydrometallurgy refers to the process of liquid-solid separation of the slurry after the neutral leaching stage. Its core function is to separate the neutral leaching slurry into a neutral supernatant and a neutral underflow through gravity settling, achieving efficient zinc recovery and impurity separation.

[0016] The obtained supernatant contains a large amount of zinc element and can be used for subsequent electrolytic refining of zinc.

[0017] (3) adding dilute acid to the neutral underflow solid phase obtained in step (2) to perform hot acid leaching, and performing solid-liquid separation to obtain leaching residue and leachate;

[0018] The leaching residue obtained is enriched with a large amount of lead and silver and is used to separate and recover elements such as Pb and Ag.

[0019] (4) adding a phosphorus source to the leachate obtained in step (3), adjusting the pH to co-precipitate ferric phosphate, and filtering to obtain precipitated ferric phosphate and a liquid phase;

[0020] The liquid phase is returned to step (2) to replace the dilute sulfuric acid for leaching the roasted ore.

[0021] The liquid phase contains part of zinc and a large amount of sulfuric acid, which is returned to step (2) for zinc recovery and is used to leach the roasted ore instead of the dilute sulfuric acid in step (2).

[0022] (5) The iron phosphate precipitated in step (4) is filtered, washed, and heat-treated for crystallization to obtain battery-grade iron phosphate.

[0023] Furthermore, in step (1), the mass content of zinc in the raw zinc concentrate is 30% to 70% (preferably 40% to 60%), and the mass content of iron is 3% to 20% (preferably 5% to 15%).

[0024] Furthermore, in step (1), the calcination temperature is 850-1050°C, preferably 900°C. Studies have shown that if the calcination temperature is too low, desulfurization will be insufficient, while if the calcination temperature is too high, the sulfate will be completely decomposed. The calcination time is preferably 3 hours or more, more preferably 4-8 hours. The calcination is to convert ZnS into ZnO.

[0025] Furthermore, the dilute sulfuric acid in step (2) has a lower quality requirement and can be prepared by using the waste liquid from electrolytic refining and the dilute sulfuric acid therein.

[0026] Furthermore, in step (2), the oxidant is at least one of air, oxygen, hydrogen peroxide, potassium permanganate, manganese dioxide, and lead dioxide.

[0027] Furthermore, in step (2), the system pH should be adjusted to 5.0-5.4 to ensure that Zn does not hydrolyze and other elements can be precipitated to the greatest extent, preferably pH = 5.2.

[0028] Furthermore, in step (2), the leaching temperature is 60-75° C. (preferably 70° C.), and the leaching time is 1-2 h (preferably 1 h).

[0029] Furthermore, in step (2), the supernatant after solid-liquid separation of the neutral concentrate is enriched in zinc and has a composition of 140-170 g / L zinc, <0.1 g / L iron, and <0.1 g / L other metal elements. This is the pre-solution for industrial electrolytic zinc ingot production.

[0030] Furthermore, in step (3), hot acid leaching is performed with dilute acid, wherein the dilute acid is concentrated sulfuric acid, the leaching temperature is 85-100° C. (preferably 90° C.), the leaching time is 2-4 h (preferably 3 h), and the leaching endpoint pH is 2-3 (preferably 2.5).

[0031] Furthermore, the phosphorus source added in step (4) is phosphoric acid, and the concentration of the phosphoric acid is controlled to be 0.1 to 0.3 mol / L (preferably 0.2 mol / L). The pH of the solution is adjusted to 1.8 to 2.3, preferably 1.8, using ammonia water. The molar ratio of phosphoric acid to metal element (P / M value) is controlled to be 1.00 to 1.05:1, preferably 1.03:1.

[0032] Furthermore, step (4) is a co-precipitation synthesis method of iron phosphate, which controls the co-precipitation conditions and utilizes elements in the concentrate, such as Cu, Ni, Co, etc., to obtain element-doped iron phosphate to improve the performance of the product.

[0033] Furthermore, in step (5), the heat treatment crystallization temperature is 200-500° C., preferably 300-400° C. A heat treatment temperature that is too high will cause an undesirable phase change of the iron phosphate, while a temperature that is too low will not achieve the crystallization effect.

[0034] The present invention addresses the technical issues of low iron resource utilization and high processing costs in the hydrometallurgical zinc production process and provides a method for preparing battery-grade iron phosphate from zinc concentrate. The method combines the iron removal step in the hydrometallurgical zinc production process with the co-precipitation process for preparing iron phosphate. More specifically, the zinc concentrate is first crushed and roasted, and then dilute sulfuric acid and manganese dioxide are added for neutral leaching. The leachate is then purified and electrolyzed to obtain zinc ingots. The solid phase leached in the previous step is then subjected to hot acid leaching, and the waste liquid is added with a phosphorus source, the pH is adjusted, and hydrated iron phosphate is synthesized using a homogeneous precipitation technique. Finally, battery-grade iron phosphate is obtained through heat treatment. The iron phosphate prepared by this method has high crystallinity, and its iron-phosphorus content, tap density, and impurity element content all meet the requirements of battery-grade iron phosphate. The present invention uses the iron resources that need to be removed during the hydrometallurgical zinc production process as raw materials to synthesize battery-grade iron phosphate, which not only meets the iron removal requirements of the original hydrometallurgical zinc production process, but also realizes the comprehensive recovery and utilization of iron.

[0035] The present invention addresses the technical problem of the difficulty in recycling the large amount of waste liquid generated in the coprecipitation process for preparing ferric phosphate. It provides a method that combines wet zinc smelting with coprecipitation to prepare ferric phosphate. Specifically, the waste liquid (acidic) generated by coprecipitation to prepare ferric phosphate is recycled into the neutral leaching process step of zinc smelting. The acidic waste liquid assists in the neutral leaching of the roasted ore, reducing the use of sulfuric acid in the zinc smelting process and the discharge of waste liquid from the coprecipitation process for preparing ferric phosphate. This method not only achieves the iron removal requirement in the zinc smelting process, but also enables the recycling of waste liquid from the coprecipitation process for preparing ferric phosphate.

[0036] Compared with the prior art, the present invention has the following advantages:

[0037] (1) The present invention combines the iron removal process in the hydrometallurgical zinc smelting process with the preparation process of battery-grade ferric phosphate, making full use of the iron resources in the zinc ore, thereby achieving high-quality utilization of the iron resources in the zinc ore and reducing iron slag emissions at the source and achieving green and clean production in the zinc smelting process.

[0038] (2) The present invention recycles the waste liquid (acidic) generated by co-precipitation to prepare ferric phosphate into the zinc smelting process. The acidic waste liquid assists in neutral leaching of the roasted ore, reducing the use of sulfuric acid in the zinc smelting process and reducing the discharge of waste liquid in the co-precipitation process to prepare ferric phosphate.

[0039] (3) The present invention can utilize metal elements (such as Cu, Mn, Co, etc.) in the roasted ore during the coprecipitation process to obtain element-doped iron phosphate, thereby improving the performance of the iron phosphate.

[0040] (4) The preparation process of the present invention is compatible with the general hydrometallurgical zinc smelting process and is easy to produce on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is the XRD pattern of the product of Example 1 of the present invention;

[0042] Figure 2 This is a SEM image of the product of Example 1 of the present invention. DETAILED DESCRIPTION

[0043] The present invention is further described in detail below with reference to specific examples. The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0044] In this specification, unless otherwise specified, the percentages are by mass.

[0045] Example 1

[0046] The method of removing iron from zinc phosphate by hydrometallurgy and co-producing battery-grade iron phosphate in this embodiment includes the following steps:

[0047] (1) crushing and grinding the zinc concentrate and passing it through a 200-mesh sieve, and then oxidizing and roasting it at 900° C. to obtain roasted ore sand;

[0048] (2) 10 g of the calcined sand obtained in step (1) and 0.5 g of manganese dioxide were added to 100 ml of 1 mol / L sulfuric acid, the leaching temperature was 70° C., the leaching time was 1 h, the stirring speed was 200 r / min, and the pH at the reaction end point was 5.2; the mixed solution was then allowed to stand at room temperature, and then solid-liquid separation was performed, which is called neutral concentration, to obtain a neutral underflow solid phase and a neutral supernatant;

[0049] The neutral supernatant obtained in step (2) can be purified industrially to obtain zinc ingots.

[0050] (3) 5 g of the neutral underflow solid phase obtained in step (2) was added to 100 ml of a 1 mol / L sulfuric acid solution, and leached for 3 h at a leaching temperature of 90° C., a stirring speed of 200 r / min, and a leaching end point pH of 2.5; after solid-liquid separation, a leaching residue and a leachate were obtained; the obtained leaching residue contained lead and silver precious metals;

[0051] (4) 25 ml of the leachate obtained in step (3) was added. The iron content in the solution was 0.45 mol / L, so 110 ml of 0.1 mol / L phosphoric acid solution was added to ensure that the phosphorus-iron molar ratio was 1.03:1; the mixture was stirred for 10 min, and then ammonia water was added to adjust the pH of the solution to 1.8 to precipitate the iron phosphate. The solid-liquid separation was performed to obtain precipitated iron phosphate and a liquid phase; the liquid phase was transferred to step (2);

[0052] (5) The iron phosphate hydrate precipitate obtained in step (4) is filtered and washed, and then sintered at 300° C. to de-crystallize to obtain battery-grade iron phosphate.

[0053] The composition of the raw zinc concentrate of this embodiment is shown in Table 1; the element content distribution of the supernatant solution after neutral concentration in step (2) is shown in Table 2; and the element content of the liquid phase after solid-liquid separation after iron removal in step (4) is shown in Table 3.

[0054] Figure 1 is the XRD pattern of the product of Example 1 of the present invention; Figure 2 This is a SEM image of the product of Example 1 of the present invention.

[0055] Figure 1 The XRD pattern shows that the present invention successfully obtains iron phosphate. Figure 2 The SEM image shows that the iron phosphate obtained by the present invention has good crystallinity and is similar to the currently commercially available iron phosphate in terms of particle size.

[0056] The battery-grade iron phosphate obtained in this example was tested for component content. The test standards and results are shown in Table 4.

[0057] Example 2

[0058] This example differs from Example 1 in that different zinc concentrate raw materials are used, and the differences in their contents are shown in Table 1. Compared with Example 1, the zinc concentrate used in this example has a lower zinc content and a higher iron content. However, the XRD patterns of the resulting ferric phosphate are essentially the same.

[0059] The battery-grade iron phosphate obtained in this example was tested for component content. The test standards and results are shown in Table 4.

[0060] Example 3

[0061] This embodiment differs from embodiment 1 in that, in step (4), 25 ml of the liquid supernatant from step (3) is first taken and then 0.25 g of CuSO4·5H2O is dissolved therein. The other steps remain unchanged, and the pH is adjusted to 2 to obtain Cu-doped iron phosphate. Cu-doped iron phosphate has excellent performance in related research. In this study, by adding a small amount of copper salt, the Cu element in the zinc smelting process is not only refined but also the performance of the iron phosphate battery can be improved.

[0062] The battery-grade iron phosphate obtained in this example was tested for component content. The test standards and results are shown in Table 4.

[0063] Example 4

[0064] This embodiment differs from embodiment 1 in that the dilute sulfuric acid used in step (2) is obtained from the waste liquid in step (4), and the other steps remain unchanged. In this embodiment, 100 ml of waste liquid is added to 2.2 ml of concentrated sulfuric acid to obtain a 1.0 mol / L sulfuric acid solution for the neutral leaching process.

[0065] The battery-grade iron phosphate obtained in this example was tested for component content. The test standards and results are shown in Table 4.

[0066] Comparative Example 1

[0067] This comparative example uses a conventional wet zinc smelting iron removal process. Compared with Example 1, the difference is that in step (4), 50 ml of the liquid supernatant obtained in step (3) is taken, 2.13 g of sodium sulfate is added, and the zinc roasted sand in step (1) is used as a regulator to continuously adjust the pH to maintain it at 1.5. After continuously stirring the reaction for 1 hour, the iron removal filtrate and filter cake are obtained by filtration. This scheme uses a conventional wet zinc smelting iron removal process. After the iron removal process in Comparative Example 1, the element ratios of the iron removal liquids of the two are shown in Table 2. It shows that the phosphate iron removal of the embodiment of the present invention has an iron removal efficiency similar to that of the comparative example wet zinc smelting process.

[0068] Table 1 Example of zinc concentrate composition (mass percentage)

[0069] Concentrate Source Zn Fe S Pb Cu other Example 1 A mine in Gansu 55.1 4.4 30.4 1.1 0.4 8.6 Example 2 A mine in Hunan 44.8 15.6 32.4 1.0 0.6 5.6

[0070] Table 2 Element distribution of neutral concentrated liquid (g / L)

[0071] element Zn Fe Cu Mn Cd Co Pb S F Example 1 140 0.03 0.02 0.04 0.05 0.005 0.001 0.015 0.8

[0072] Table 3 Distribution of liquid elements after iron removal

[0073]

[0074] Table 4 Test results of the composition of the products of iron phosphate and battery-grade iron phosphate obtained in Examples 1-3

[0075]

[0076]

Claims

1. A method for removing iron from zinc phosphate by wet process and co-producing battery-grade iron phosphate, characterized in that: The following steps are involved: (1) crushing and classifying the zinc concentrate, and oxidizing and roasting it to obtain roasted ore; (2) adding dilute sulfuric acid or spent electrolyte to the roasted ore obtained in step (1), adding an oxidant, controlling the pH of the system, oxidizing and leaching to obtain a neutral leachate, and allowing the leachate to stand for solid-liquid separation to obtain a neutral underflow solid phase and a neutral supernatant; (3) adding dilute acid to the solid phase obtained in step (2) to perform hot acid leaching, and performing solid-liquid separation to obtain leaching residue and leachate; (4) adding a phosphorus source to the leachate obtained in step (3), and adjusting the pH to co-precipitate and prepare ferric phosphate; obtaining precipitated ferric phosphate and a liquid phase; The liquid phase is returned to step (2) to replace the dilute sulfuric acid for leaching the roasted ore; (5) The iron phosphate precipitated in step (4) is filtered, washed, and heat-treated for crystallization to obtain battery-grade iron phosphate.

2. The method for removing iron from zinc phosphate and co-producing battery-grade iron phosphate according to claim 1, characterized in that: In step (1), the mass content of zinc in the raw zinc concentrate is 30% to 70%, and the mass content of iron is 3% to 20%.

3. The method for removing iron from zinc phosphate and co-producing battery-grade iron phosphate according to claim 1 or 2, characterized in that: In step (1), the calcination temperature is 850-1050°C.

4. The method for removing iron from zinc phosphate and co-producing battery-grade iron phosphate according to claim 1 or 2, characterized in that: In step (2), the oxidant is at least one of air, oxygen, hydrogen peroxide, potassium permanganate, manganese dioxide, and lead dioxide.

5. The method for removing iron from zinc phosphate and co-producing battery-grade iron phosphate according to claim 1 or 2, characterized in that: In step (2), the system pH should be adjusted to 5.0-5.4; and / or, the amount of sulfuric acid used is determined by precise control of the pH, and sulfuric acid is industrially prepared using the electrolyte remaining in the zinc electrolysis process; and / or, the amount of the oxidant used is based on the standard of being able to completely oxidize the ferrous ions in the roasted ore; and / or, in step (2), the leaching temperature is 60-75° C., and the leaching time is 1-2 hours.

6. The method for removing iron from zinc phosphate and co-producing battery-grade iron phosphate according to claim 1 or 2, characterized in that: In step (2), the supernatant after solid-liquid separation of the neutral concentrate is enriched with zinc, and its composition is: Contains zinc 140-170g / L, iron <0.1g / L, and other metal elements <0.1g / L.

7. The method for removing iron from zinc phosphate and co-producing battery-grade iron phosphate according to claim 1 or 2, characterized in that: In step (3), hot acid leaching is performed, the leaching temperature is 85-100° C., the leaching time is 2-4 hours, and the leaching end point pH is 2-3.

8. The method for removing iron from zinc phosphate and co-producing battery-grade iron phosphate according to claim 1 or 2, characterized in that: The phosphorus source added in step (4) is phosphoric acid, and the concentration of the phosphoric acid is controlled to be 0.1-0.3 mol / L; and / or, ammonia water is used to adjust the pH of the solution to 1.8-2.3; and / or, the molar ratio of phosphoric acid to metal element is controlled to be 1.00-1.05:

1.

9. The method for removing iron from zinc phosphate and co-producing battery-grade iron phosphate according to claim 1 or 2, characterized in that: Step (4) is a co-precipitation synthesis method of ferric phosphate, which controls the co-precipitation conditions and utilizes the elements Cu, Ni, and Co in the concentrate to obtain element-doped ferric phosphate.

10. The method for removing iron from zinc phosphate and co-producing battery-grade iron phosphate according to claim 1 or 2, characterized in that: In step (5), the heat treatment crystallization temperature is 200-500°C.

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