A method for preparing battery-grade iron phosphate by utilizing iron resources in high-iron zinc leaching residue

Abstract

The application discloses a method for preparing battery-grade iron phosphate by using iron resources in high-iron zinc leaching residue, and belongs to the technical field of solid waste resource utilization. The method first reduces and acid-leaches the high-iron zinc leaching residue, uses ammonia and iron powder to neutralize and hydrolyze the obtained leaching solution to remove aluminum, and obtains an aluminum-removed solution; a phosphorus source and an oxidizing agent are added to the aluminum-removed solution to perform a precipitation reaction, and a crude iron phosphate precipitate is obtained; the crude iron phosphate precipitate is slurried and reacted at a proper temperature and pH to obtain battery-grade dihydrate iron phosphate. The method can realize efficient leaching of iron metal resources in the high-iron zinc leaching residue, realize deep separation of iron ions from impurities such as zinc ions and aluminum ions, and further obtain battery-grade iron phosphate, so that efficient recovery and high-value utilization of the difficult-to-utilize iron resources in the high-iron zinc leaching residue are realized.

Description

Technical Field

[0001] This invention relates to a method for the resource utilization of high-iron zinc leaching residue, specifically a method for preparing battery-grade iron phosphate using iron resources in high-iron zinc leaching residue, belonging to the field of solid waste resource utilization technology. Background Technology

[0002] As one of the mainstream products in the power battery field, lithium iron phosphate (LiFePO4) batteries have seen their market share continue to rise due to their cost advantages, safety performance, and cycle life. Battery-grade iron phosphate (FePO4) is the core precursor for synthesizing LiFePO4 cathodes, and the stability of its raw material supply and cost control directly affect the competitiveness of the entire industry chain. However, the iron source currently used in iron phosphate production is highly dependent on high-purity iron powder or iron salts. These raw materials are not only expensive but also have limited availability, becoming one of the bottlenecks restricting cost reduction and efficiency improvement in the industry.

[0003] Meanwhile, the zinc smelting industry faces the dual pressures of solid waste disposal and resource waste. During the "roasting-leaching-purification-electrowinning" process of producing metallic zinc from zinc sulfide concentrate, most of the iron is converted into structurally stable zinc ferrite and enriched in the leaching residue. In addition to valuable metals such as zinc and lead, the iron content in zinc smelting leaching residue is typically as high as 20% to 30%, indicating a significant resource endowment. While current mainstream pyrometallurgical volatilization or hot acid leaching processes can partially recover zinc and lead, iron resources are often not effectively utilized, ultimately ending up as waste residue piled up or landfilled. This not only results in resource idleness but also poses a long-term threat to the ecological environment due to the risk of heavy metal leaching. Currently, some pyrometallurgical combined with hydrometallurgical processes can recover iron and zinc from zinc smelting leaching residues. However, these processes are relatively complex, costly, and have low iron resource utilization rates. For example, Chinese patent (authorization announcement number: CN111286600B) discloses a method for efficiently recovering zinc and iron from zinc ferrate materials, including the following steps: grinding the zinc ferrate material, mixing it with sulfuric acid and sulfate, roasting it, stirring and leaching the roasted material, filtering it to obtain a zinc-iron solution and filter residue; removing iron from the zinc-iron solution using the goethite method to obtain goethite slag; and extracting and electrowinning the zinc solution after iron removal to obtain electrolytic zinc products, with a zinc recovery rate >98% and an iron recovery rate >95%.

[0004] Therefore, if the iron resources in high-iron zinc leaching slag can be converted into high-value-added battery-grade iron phosphate, it can not only solve the problem of low iron utilization in the zinc smelting industry, but also open up a new path for low-cost and sustainable iron source supply for the iron phosphate industry. Although existing research has involved the comprehensive recovery of valuable metals in zinc smelting slag, there are no reports on the direct preparation of high-value battery-grade iron phosphate using high-iron zinc leaching slag as a single iron source. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing battery-grade iron phosphate from iron resources in high-iron zinc leaching residue. This method enables efficient leaching of iron metal resources from high-iron zinc leaching residue and deep separation of iron ions from impurities such as zinc and aluminum ions, thereby obtaining high-purity battery-grade iron phosphate. This method achieves efficient recovery and high-value utilization of difficult-to-utilize iron resources in high-iron zinc leaching residue. Furthermore, the method is simple to operate, low in cost, and low in energy consumption, making it suitable for industrial production.

[0006] To achieve the above-mentioned technical objectives, the present invention provides a method for preparing battery-grade iron phosphate using iron resources in high-iron zinc leaching residue, which includes the following steps:

[0007] 1) Using sulfuric acid as the leaching agent and iron powder as the reducing agent, the high-iron zinc leaching residue was subjected to reducing acid leaching to obtain Fe-containing... 2+ Zn 2+ And Al 3+ Leachate and lead-enriched residue;

[0008] 2) The leachate is neutralized and hydrolyzed with ammonia and iron powder to remove aluminum, yielding a solution containing Fe. 2+ and Zn 2+ Aluminum removal liquid and aluminum dross;

[0009] 3) A phosphorus source and oxidant are added to the aluminum removal solution to carry out a precipitation reaction, resulting in crude iron phosphate precipitate and Zn-containing precipitate. 2+ The solution;

[0010] 4) The crude ferric phosphate precipitate is slurried and the pH of the system is adjusted to below 1.0. The reaction is carried out at 90~110℃ for 7~12 h to obtain battery-grade ferric phosphate dihydrate.

[0011] The iron content of the high-iron zinc leaching residue involved in this invention is generally 15% to 30%, and the main phase it contains is ZnFe2O4 (mainly containing Fe and Zn, and containing impurities such as Al, Pb, Cd, Ca, Cu, Mg, Mn, etc.).

[0012] The key to this invention's process for preparing battery-grade iron phosphate from iron-zinc leaching residue lies in employing a combination of "reduction leaching from iron-zinc leaching residue" and "stepwise removal of Al." 3+ and Zn 2+The combined process of "+" and "segmented synthesis of crude iron phosphate" enables efficient leaching of iron metal resources from high-iron zinc leaching residue, achieving deep separation of iron ions from impurities such as zinc and aluminum ions, and further obtaining high-purity battery-grade iron phosphate. This truly realizes the efficient recovery and high-value utilization of difficult-to-use iron resources in high-iron zinc leaching residue. More specifically, since the iron in zinc smelting leaching residue mainly exists in the relatively stable zinc ferrite phase, it is difficult to achieve efficient leaching of iron using conventional leaching methods. This invention uses iron powder to promote the leaching of iron from high-iron zinc leaching residue, using iron powder as a reducing agent to remove Fe from the leaching system. 3+ Reduced to Fe 2+ This lowers the redox potential of the solution and breaks down Fe. 3+ The cumulative effect of inhibiting the dissolution of zinc ferrite accelerates the destruction of the spinel structure and promotes efficient iron leaching, significantly improving the iron leaching rate. The main impurities in the leachate are aluminum and zinc ions. While aluminum ions readily hydrolyze and precipitate, they easily carry away iron and zinc ions, leading to their loss. This invention uses ammonia and iron powder as synergistic neutralizing and hydrolyzing agents. Ammonia primarily adjusts the pH, while iron powder stabilizes it, preventing rapid pH changes that could cause co-precipitation of metal ions. Simultaneously, iron powder prevents the oxidation of ferrous iron to ferric iron, thus reducing the iron precipitation rate. Therefore, their synergistic effect minimizes the loss of iron and zinc. The removal of zinc ion impurities is mainly achieved by controlling the synthesis process of iron phosphate. First, a precipitation reaction is used to utilize the low solubility of iron phosphate formed from ferric iron, leaving most of the zinc in the solution. For the small amount of zinc impurities mixed in with iron phosphate, this invention re-slurryesizes the iron phosphate precipitate and reacts under strictly controlled conditions such as pH and temperature. This reaction process mainly involves dissolving and recrystallizing the low-crystallinity iron phosphate, causing the co-precipitated zinc, calcium, and other impurities to dissolve again and inhibiting the entry of zinc ions, calcium ions, and other impurities into the iron phosphate lattice. Moreover, it can regulate the growth of iron phosphate crystals, improve the crystal morphology and particle size distribution of iron phosphate products, and thus ensure that the purity, particle size, and morphology of iron phosphate meet the requirements of battery grade.

[0013] As a preferred embodiment, the conditions for the reducing acid leaching are: a leaching liquid-to-solid ratio of 3-8 mL:1 g, a leaching temperature of 50-95°C, and a leaching time of 2-6 h. Under these preferred reducing acid leaching conditions, a high iron leaching rate can be guaranteed. The leaching temperature is further preferably 60-80°C.

[0014] As a preferred embodiment, during the reducing acid leaching process, the amount of sulfuric acid used is 1.05 to 1.35 times the theoretical amount of sulfuric acid required to completely convert the iron in the ferrous zinc leaching residue into ferrous sulfate, and the amount of iron powder used is 0.8 to 1.3 times the theoretical amount of iron powder required to completely convert the iron in the ferrous zinc leaching residue into ferrous sulfate. The main component of the ferrous zinc leaching residue is zinc ferrate, and its leaching reaction formula is as follows: ZnFe₂O₄ + 4H₂SO₄ + Fe → ZnSO₄ + 3FeSO₄ + 4H₂O.

[0015] As a preferred embodiment, the process of neutralization and hydrolysis to remove aluminum is as follows: First, ammonia is added to pre-neutralize the pH to a range of 3.0-4.0, then iron powder is added to stabilize the pH at 4.2-5.0, and the temperature is controlled at 50-95℃ for 1-6 hours. The amount of iron powder added is such that the concentration reaches 0.25-5 g / L; more preferably, the concentration reaches 0.5-1 g / L. If ammonia is used alone to adjust the pH, the pH environment is unstable, easily causing co-precipitation loss of zinc ions and ferrous ions. Introducing iron powder can stabilize the pH, and at the same time, iron powder can prevent ferrous ions from being oxidized to Fe. 3+ Premature hydrolysis interferes with the aluminum removal effect. This invention first uses ammonia to consume most of the free acid, then adds iron powder to react with the residual acid, ultimately stabilizing the pH of the system within the range of 4.2-5.0 to maintain Al... 3+ The optimal pH environment for hydrolysis precipitation to achieve Al 3+ Selective deep removal. Further preferred method: pre-neutralize with ammonia to a pH range of 3.5–4.0.

[0016] As a preferred embodiment, the precipitation reaction conditions are: temperature 40~80℃, pH 1.2~1.8, and time 0.5~3h. Under these preferred precipitation reaction conditions, iron ions can be selectively converted into iron phosphate, achieving preliminary separation from zinc ions.

[0017] As a preferred embodiment, during the precipitation reaction, the amount of oxidant used is 1 to 1.5 times the theoretical amount of oxidant required to completely convert ferrous ions into ferric ions, and the amount of phosphorus source used is based on Fe... 3+ With PO4 3- The molar ratio is 1:(1.0~1.2). The reaction formula for the precipitation reaction is as follows, taking hydrogen peroxide as the oxidant as an example: 2FeSO4 + H2O2 + H2SO4 → Fe2(SO4)3 + 2H2O.

[0018] As a preferred embodiment, the phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, or calcium dihydrogen phosphate. These phosphorus sources are highly water-soluble and can ionize into phosphate ions after dissolving in water, making them common phosphorus sources for the preparation of iron phosphate.

[0019] As a preferred embodiment, the oxidant includes hydrogen peroxide. Hydrogen peroxide is preferred as the oxidant because it does not introduce new impurities.

[0020] As a preferred embodiment, the liquid-to-solid ratio is controlled to be (1.5~8) mL:1g during the pulping process.

[0021] The crude ferric phosphate precipitate of the present invention is pulped and the pH of the system is adjusted to 0.4-0.8. Within the preferred pH range, the zinc content in the ferric phosphate product can be kept low. More preferably, the crude ferric phosphate precipitate of the present invention is pulped and the pH of the system is adjusted to 0.4-0.8, and the reaction is carried out at 90-100°C for 7-12 hours to obtain battery-grade ferric phosphate dihydrate. By synergistically controlling temperature and pH, the impurity content can be minimized and the morphology of ferric phosphate crystals can be improved. Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0022] This invention uses high-iron zinc leaching residue, a hazardous solid waste generated from hydrometallurgical zinc smelting, as a raw material to replace traditional iron powder and iron salts, greatly reducing the production cost of iron phosphate and solving the storage pressure and environmental risks of zinc smelting enterprises.

[0023] This invention employs a reduction leaching method for zinc smelting leaching residue to achieve efficient leaching of iron from the residue. This solves the technical problem that iron in zinc smelting leaching residue mainly exists as a relatively stable zinc ferrite phase, making it difficult to achieve efficient leaching of iron using conventional leaching methods.

[0024] This invention employs ammonia and iron powder as synergistic neutralizing and hydrolyzing agents in the process of aluminization by neutralization and hydrolysis. Ammonia rapidly neutralizes free acid, while iron powder stabilizes the pH, preventing rapid pH changes that could cause co-precipitation of metal ions. Simultaneously, iron powder prevents the oxidation of ferrous iron to ferric iron, thus avoiding an increased iron precipitation rate. Therefore, the synergistic effect of these two agents can effectively neutralize free acid during the aluminization process. 3+ While reducing the concentration to below 60 ppm, it significantly reduces the co-precipitation loss of zinc and iron.

[0025] The iron phosphate preparation process of this invention adopts a segmented synthesis strategy of "one-stage low pH nucleation - two-stage high acidity crystallization", which can effectively suppress impurities from entering iron phosphate. At the same time, it can control the particle size, crystallinity, morphology, etc. of iron phosphate to obtain battery-grade iron phosphate with purity, iron-phosphorus ratio, tap density, and impurity content that meet the standard of "Iron Phosphate for Batteries" (HG / T 4701-2021).

[0026] The present invention enables the simultaneous recovery of zinc resources from zinc smelting leaching residue, and the zinc-containing molten liquid can be returned to the hydrometallurgical zinc smelting system or used to prepare zinc products, thus realizing comprehensive resource recovery. Attached Figure Description

[0027] Figure 1 This is a process flow diagram for preparing battery-grade iron phosphate from the iron-zinc leaching residue of this invention.

[0028] Figure 2 The image shows the XRD pattern of the ferrous zinc leaching residue. Detailed Implementation

[0029] The following specific embodiments are intended to further illustrate the content of the present invention, rather than to limit the scope of protection of the claims.

[0030] In the following embodiments, the elemental composition of the high-ferric zinc leaching residue is shown in Table 1 below. Its main phase is zinc ferrite, for example, its XDR image is shown below. Figure 2 As shown.

[0031]

[0032] Example 1

[0033] Iron powder-sulfuric acid reduction leaching: 50g of high-ferric zinc leaching residue was ground and passed through a 100-mesh sieve. Sulfuric acid solution was added at a liquid-to-solid ratio of 4:1 mL / g (the amount of sulfuric acid used was 1.05 times the theoretical amount), along with an appropriate amount of reduced iron powder (1.05 times the theoretical amount). Leaching was carried out at 70℃ with stirring at 300 r / min for 3 h. After leaching, a first solid-liquid separation was performed to obtain the leachate and a leaching residue rich in lead and silver. Analysis showed that the Zn leaching rate was 99.99%, the Fe leaching rate was 97.61%, and the Al leaching rate was 74.24%.

[0034] The specific operating conditions for the control group are the same as in Example 1, with the following differences:

[0035] 1) A control group was set up by using different amounts of sulfuric acid. The results are shown in Table 2 below:

[0036]

[0037] 2) A control experimental group was set up using different reaction temperatures, and the results are shown in Table 3 below:

[0038]

[0039] 3) A control group was set up with different amounts of iron powder, and the results are shown in Table 4 below:

[0040]

[0041] Example 2

[0042] Ammonia-Iron Powder Combined Aluminum Removal: 100 mL of the leachate from Example 1 was placed in a beaker. First, ammonia (volume ratio 1:1) was added dropwise for pre-neutralization. The temperature was set to 60°C, and the pH of the solution was adjusted to 4, consuming most of the free acid. Then, 0.1 g of reduced iron powder was added, and the reaction continued for 2 hours. The reaction between the iron powder and the residual acid raised the pH of the system to 4.5, simultaneously removing residual Fe from the solution. 3+ Reduced to Fe 2+ After the reaction was completed, a second solid-liquid separation was performed to obtain the aluminum-removed liquid and aluminum slag. Analysis showed that the Al content in the filtrate decreased to 35 ppm, the Zn loss rate was 9.1%, and the Fe loss rate was 7.7%.

[0043] The specific operating conditions for the control group are the same as in Example 2, with the following differences:

[0044] 1) Control groups were set up using different pre-neutralization pH values, and the results are shown in Table 5 below:

[0045]

[0046] 2) A control group was set up with different amounts of reduced iron powder. The results are shown in Table 6 below:

[0047]

[0048] Example 3

[0049] Iron phosphate synthesis in one stage: Ammonium dihydrogen phosphate was added as a phosphorus source to the aluminum-removed solution from Example 2 to control the Fe content. 3+ With PO4 3- The molar ratio is 1:1.05. Slowly add 30% hydrogen peroxide (1.2 times the theoretical amount) to Fe... 2+ Oxidized to Fe 3+ The reaction temperature was controlled at 60℃, the pH of the system was adjusted to 1.5±0.1, and the reaction was stirred for 0.5 h before a third solid-liquid separation was performed to obtain crude iron phosphate precipitate and zinc-containing filtrate. The iron removal rate during the iron precipitation process was 96.98%, the zinc loss rate was 0.86%, and the iron-zinc ratio of the solution was 264:1.

[0050] The specific operating conditions for the control group are the same as in Example 3, with the following differences:

[0051] 1) A control experimental group was set up using different pH values, and the results are shown in Table 7 below:

[0052]

[0053] 2) A control group was set up at different temperatures, and the results are shown in Table 8 below:

[0054]

[0055] Example 4

[0056] The crude ferric phosphate filter cake obtained in Example 3 was transferred to a reactor, and pure water was added at a liquid-to-solid ratio of 2:1 (mL / g). Sulfuric acid solution was added dropwise to adjust the pH of the system to 0.4. The reaction was stirred at 95°C for 8 h to allow the crystals to grow fully and release the adsorbed zinc ions. After the reaction was completed, a fourth solid-liquid separation was performed to obtain a high-purity ferric phosphate dihydrate filter cake.

[0057] The specific operating conditions for the control group are the same as in Example 4, with the following differences:

[0058] 1) Control experimental groups were set up using different pH values, and the results are shown in Table 9 below.

[0059]

[0060] 2) A control group was set up at different temperatures, and the results are shown in Table 10 below:

[0061]

[0062] The obtained filter cake was washed with pure water until neutral and dried at 80℃ for 12 h to obtain battery-grade iron phosphate dihydrate. Testing showed that the product had an iron-to-phosphorus ratio of 0.982, a purity of 99.25%, a particle size (D50) of 4.817 μm, and the content of all impurities met the standards (as shown in Table 2). All indicators complied with the standard of "Battery-grade Iron Phosphate" (HG / T 4701-2021).

[0063]

Claims

1. A method for preparing battery-grade iron phosphate using iron resources from high-iron zinc leaching residue, characterized in that: Includes the following steps: 1) Using sulfuric acid as the leaching agent and iron powder as the reducing agent, the high-iron zinc leaching residue was subjected to reducing acid leaching to obtain Fe-containing... 2+ Zn 2+ And Al 3+ The leachate and lead-enriched slag; 2) the leachate is neutralized and hydrolyzed with ammonia and iron powder to remove aluminum, yielding Fe-containing slag. 2+ and Zn 2+ Aluminum removal liquid and aluminum dross; 3) A phosphorus source and oxidant are added to the aluminum removal solution to carry out a precipitation reaction, resulting in crude iron phosphate precipitate and Zn-containing precipitate. 2+ 4) The crude ferric phosphate precipitate is slurried and the pH of the system is adjusted to below 1.

0. The reaction is carried out at 90~110℃ for 7~12 h to obtain battery-grade ferric phosphate dihydrate.

2. The method for preparing battery-grade iron phosphate using iron resources in high-iron zinc leaching residue according to claim 1, characterized in that: The conditions for the reducing acid leaching are: a leaching liquid-to-solid ratio of 3-8 mL:1 g, a leaching temperature of 50-95 °C, and a leaching time of 2-6 h.

3. A method for preparing battery-grade iron phosphate using iron resources in high-iron zinc leaching residue according to claim 1 or 2, characterized in that: In the reduction acid leaching process, the amount of sulfuric acid used is 1.05 to 1.35 times the theoretical amount of sulfuric acid required to convert all the iron in the ferrous zinc leaching residue into ferrous sulfate, and the amount of iron powder used is 0.8 to 1.3 times the theoretical amount of iron powder required to convert all the iron in the ferrous zinc leaching residue into ferrous sulfate.

4. The method for preparing battery-grade iron phosphate from iron resources in high-iron zinc leaching residue according to claim 1, characterized in that: The process of neutralizing and dealuminizing by water is as follows: first, ammonia water is added to pre-neutralize the pH to a range of 3.0~4.0, then iron powder is added to stabilize the pH at 4.2~5.0, and the temperature is controlled at 50~95℃ for 1~6 hours.

5. The method for preparing battery-grade iron phosphate from iron resources in high-iron zinc leaching residue according to claim 1, characterized in that: The precipitation reaction conditions are: temperature 40~80℃, pH 1.2~1.8, and time 0.5~3h.

6. A method for preparing battery-grade iron phosphate from iron resources in high-iron zinc leaching residue according to claim 1 or 5, characterized in that: During the precipitation reaction, the amount of oxidant used is 1 to 1.5 times the theoretical amount of oxidant required to completely convert ferrous ions into ferric ions, and the amount of phosphorus source used is based on Fe... 3+ With PO4 3- The molar ratio is 1:(1.0~1.2).

7. A method for preparing battery-grade iron phosphate from iron resources in high-iron zinc leaching residue according to claim 6, characterized in that: The phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, or calcium dihydrogen phosphate. The oxidizing agent includes hydrogen peroxide.

8. The method for preparing battery-grade iron phosphate from iron resources in high-iron zinc leaching residue according to claim 1, characterized in that: During the pulping process, the liquid-to-solid ratio is controlled at (1.5~8) mL:1g.

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