A method and system for preparing ferric phosphate based on continuous acid hydrolysis of ferric phosphide powder

Abstract

This invention discloses a method and system for preparing iron phosphate based on continuous acid hydrolysis of iron phosphate powder, belonging to the fields of hydrometallurgy and battery material preparation technology. The method includes: adding a first oxidant to a reaction slurry containing a solution of divalent iron ions, acid, and iron phosphate powder to oxidize the Fe in the reaction slurry. 2+ Oxidized to Fe 3+ and make Fe 3+ It undergoes a redox reaction with ferric phosphide to obtain a product rich in Fe. 2+ and PO4 3‑ The leachate; at least a portion of the leachate is reacted with a second oxidizing agent to reduce the Fe in the leachate. 2+ All oxidized to Fe 3+ and PO4 3‑ Ferric phosphate is produced. This method achieves efficient and continuous dissolution of ferric phosphate by constructing an ingenious internal iron ion oxidation system, solving the technical problem of direct acid dissolution of ferric phosphate powder in existing technologies. The method has a short process, low cost, and is easy to scale up for continuous industrial production. The corresponding system setup is simple and easy to implement, making it suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the fields of hydrometallurgy and battery material preparation technology, and more specifically, to a method and system for preparing iron phosphate based on continuous acid hydrolysis of iron phosphate powder. Background Technology

[0002] Iron phosphide is an important industrial intermediate or byproduct, and may also originate from the recycling process of specific waste materials. Due to its stable crystal structure and high chemical inertness, iron phosphide is extremely difficult to dissolve in common acids (such as sulfuric acid and hydrochloric acid), which severely restricts its use as an iron and phosphorus source for high-value-added products (such as battery-grade iron phosphate).

[0003] In existing technologies, high-temperature and high-pressure leaching or the introduction of strong oxidants (such as sodium chlorate or nitric acid) are commonly used to treat such sparingly soluble materials. However, the high-temperature and high-pressure method requires sophisticated equipment, consumes a lot of energy, and has poor operational safety; while the use of liquid strong oxidants is costly, the reaction is violent and difficult to control, and may introduce new anionic impurities (such as Cl-). - NO3 - This also includes issues such as material passivation or element loss due to excessive concentration in certain areas (e.g., phosphorus escaping as PH3 gas).

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a method and system for preparing ferric phosphate based on continuous acid hydrolysis of ferric phosphate powder, so as to solve or improve at least one of the above-mentioned technical problems.

[0006] This invention can be implemented as follows: In a first aspect, the present invention provides a method for preparing ferric phosphate based on continuous acid hydrolysis of ferric phosphate powder, comprising the following steps: adding a first oxidant to a reaction slurry containing a solution of divalent ferric ions, an acid, and ferric phosphate powder, so as to oxidize the Fe in the reaction slurry. 2+ Oxidized to Fe 3+ and the generated Fe 3+ It undergoes a redox reaction with ferric phosphide to obtain a product rich in Fe. 2+ and PO4 3- The leachate; At least a portion of the leachate is reacted with a second oxidizing agent to reduce the Fe in the leachate. 2+ All oxidized to Fe 3+ and PO4 3- Iron phosphate is produced.

[0007] In an optional implementation, the solution is continuously directed towards obtaining Fe-rich... 2+ and PO4 3-Iron phosphide powder and acid are added to the leaching reaction device of the leachate, while Fe-rich solutions are continuously drawn from the leaching reaction device. 2+ and PO4 3- The leachate is used to ensure that the system in the leaching reaction apparatus always maintains Fe 2+ state.

[0008] In an optional implementation, Fe in the ferrous ion solution 2+ The molar ratio of iron phosphate powder to iron phosphate powder is 9:2 to 9:5.

[0009] In an optional embodiment, the acid includes at least one of sulfuric acid and phosphoric acid.

[0010] In an optional embodiment, the first oxidant and the second oxidant independently include at least one of oxygen, air, ozone and hydrogen peroxide.

[0011] In an optional embodiment, the first oxidant and the second oxidant independently include at least one of oxygen and air.

[0012] In an optional implementation, the generated Fe 3+ The redox reaction with ferric phosphide is carried out under conditions of pH 1.5~2 and temperature 60℃~95℃.

[0013] In an optional embodiment, the volume of leachate used to react with the second oxidant accounts for 30% to 40% of the total leachate volume, by volume percentage.

[0014] In an optional embodiment, the leachate not used for reaction with the second oxidant is returned to a Fe-rich solution. 2+ and PO4 3- In the leaching reaction apparatus of the leachate.

[0015] In an optional embodiment, the remaining leachate, excluding the leachate returned to the leaching reaction apparatus, is subjected to solid-liquid separation, and the separated liquid is used to react with the second oxidant.

[0016] In an optional embodiment, at least a portion of the leachate reacts with the second oxidant at a pH of 1.5 to 3.0 and a temperature of 50°C to 90°C.

[0017] In an optional implementation, the pH of the reaction is adjusted by adding ammonia.

[0018] Secondly, the present invention provides a system for preparing iron phosphate based on continuous acid hydrolysis of iron phosphate powder, including a leaching reaction device and a product synthesis device. The leaching reaction apparatus is used to react a reaction slurry containing a solution of ferrous ions, acid, and iron phosphide powder with a first oxidizing agent to obtain a Fe-rich solution.2+ and PO4 3- The leachate; The product synthesis apparatus is used to react at least a portion of the leachate with a second oxidant to reduce the Fe in the leachate. 2+ All oxidized to Fe 3+ and PO4 3- Iron phosphate is produced.

[0019] In optional embodiments, the leaching reaction apparatus includes a stirred tank reactor, a tower reactor, or a cascade reactor group.

[0020] In an optional embodiment, the system further includes a solid-liquid separation device for separating the leachate reacting with the second oxidant, wherein the separated liquid is used to react with the second oxidant.

[0021] In an optional implementation, the system further includes a diversion and circulation device for diverting Fe-rich water. 2+ and PO4 3- The leachate is divided into a portion that returns to the leaching reaction unit and a portion that is used to enter the product synthesis unit, and the portion that returns to the leaching reaction unit is recycled back to the leaching reaction unit.

[0022] The beneficial effects of this invention include: The present invention provides a method for preparing ferric phosphate based on continuous acid hydrolysis of ferric phosphate powder. This method involves adding a first oxidant to a reaction slurry containing a solution of ferrous ions, acid, and ferric phosphate powder to oxidize the Fe in the reaction slurry. 2+ Oxidized to Fe 3+ and the generated Fe 3+ It undergoes a redox reaction with ferric phosphide to obtain a product rich in Fe. 2+ and PO4 3- The leachate; at least a portion of the leachate is reacted with a second oxidizing agent to reduce the Fe in the leachate. 2+ All oxidized to Fe 3+ and PO4 3- Iron phosphate is produced.

[0023] The above method, by introducing a ferrous iron recycling system, transforms iron phosphide, which is difficult to dissolve directly in acid, into a form that can be efficiently and completely dissolved, thus solving a technical bottleneck in the industry. Furthermore, this method fully utilizes the iron and phosphorus elements inherent in the iron phosphide powder, resulting in a short process flow, low reagent consumption, high raw material utilization, and low overall production costs. In addition, this method does not require high-temperature roasting or high-pressure leaching, has low equipment requirements, is easy to control during operation, and has low energy consumption. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 The process flow diagram of the method for preparing iron phosphate based on continuous acid hydrolysis of iron phosphate powder provided by the present invention is shown. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0027] The method and system for preparing iron phosphate based on continuous acid hydrolysis of iron phosphate powder provided by the present invention will be described in detail below.

[0028] This invention provides a method for preparing ferric phosphate based on continuous acid hydrolysis of ferric phosphate powder, such as... Figure 1 As shown, it includes the following steps: S1: A first oxidizing agent is added to the reaction slurry containing ferrous ions, acid, and iron phosphide powder to oxidize the Fe in the reaction slurry. 2+ Oxidized to Fe 3+ and the generated Fe 3+ It undergoes a redox reaction with ferric phosphide to obtain a product rich in Fe. 2+ and PO4 3- The leachate.

[0029] In some alternative implementations, the initial ferrous ion solution may be the leaching solution of the system or a ferrous sulfate solution.

[0030] In some alternative embodiments, the acid may exemplary include at least one of sulfuric acid and phosphoric acid. When phosphoric acid is used, it may also serve to adjust the iron-to-phosphorus molar ratio in the final product, ferric phosphate.

[0031] In some alternative embodiments, the first oxidant may exemplary include at least one selected from oxygen, air, ozone, and hydrogen peroxide. In some preferred embodiments, the first oxidant may include at least one selected from oxygen and air. The actual amount of the first oxidant added may be 1 to 2 times the theoretical amount added, where the theoretical amount of the first oxidant refers to the amount of Fe... 2+ Completely formed Fe 3+ The required amount.

[0032] In some alternative implementations, Fe in the ferrous ion solution 2+ The chemical reaction equation between Fe2P and iron phosphide powder is as follows: Fe2P + 9Fe 3+ +4H₂O→11Fe 2+ +H2PO4 - +6H + ;2Fe 2+ +1 / 2O2+2H + →2Fe 3+ +H₂O. According to the above chemical reaction equation, Fe²⁺ ions in the ferrous ion solution... 2+ The stoichiometric ratio of the ferric phosphide to iron phosphide is 9:1. In actual operation, iron phosphide powder is added in excess, for example, in a solution of ferrous ions containing Fe. 2+ The molar ratio of iron phosphide powder to Fe is 9:2 to 9:5 (e.g., 9:2, 9:3, 9:4, or 9:5, etc.), that is, the amount of iron phosphide powder added is relative to the amount of Fe in the system. 3+ It is added in excess to ensure that the iron ions in the system after the reaction exist mainly in the divalent form. By controlling the amount of iron phosphide powder added, sufficient Fe can always be present in the reaction slurry before and during the reaction process after the addition of the first oxidant. 2+ To maintain the stability of the reaction and inhibit Fe 3+ Premature hydrolysis.

[0033] In some alternative implementations, the generated Fe 3+ The redox reaction with ferric phosphide is carried out under conditions of pH 1.5~2 (e.g., 1.5, 1.6, 1.7, 1.8, 1.9, or 2) and temperature 60℃~95℃ (e.g., 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, or 95℃).

[0034] In other words, the reactions in step S1 were all carried out at a pH of 1.5 to 2 (with residual acid of 10 g / L to 30 g / L) and a temperature of 60°C to 95°C.

[0035] Preferably, the first oxidant is continuously added to completely dissolve the iron phosphide powder in the reaction slurry, resulting in a Fe-rich slurry. 2+ and PO4 3- The leachate.

[0036] In some optional embodiments, step S1 described above can be carried out continuously in a single reactor or multiple reactors in series. The acid, iron phosphide powder, and the first oxidant can be added continuously or semi-continuously, and the leachate can be discharged continuously or semi-continuously to achieve continuous dissolution of the iron phosphide powder. In some preferred embodiments, by continuously adding the acid, iron phosphide powder, and the first oxidant to obtain Fe-rich solutions... 2+and PO4 3- Iron phosphide powder and acid are added (supplemented) to the leaching reaction apparatus of the leachate, while Fe-rich solution is continuously discharged (drawn out) from the leaching reaction apparatus. 2+ and PO4 3- The leachate is used to ensure that the system in the leaching reaction apparatus always maintains Fe 2+ state.

[0037] Continuing from above, step S1 involves mixing a ferrous ion solution with acid and iron phosphide powder to form a reaction slurry primarily composed of ferrous ions; then, a first oxidant is introduced into the reaction slurry. The first oxidant firstly oxidizes the Fe in the reaction slurry... 2+ Oxidized to Fe 3+ The generated Fe 3+ As a strong oxidizing agent, it immediately undergoes a redox reaction with excess iron phosphide powder in the reaction slurry, converting the iron and phosphorus in the iron phosphide powder into Fe. 2+ and PO4 3- Form dissolution, while Fe 3+ It was reduced to Fe 2+ This achieves complete dissolution of iron phosphide powder. The above "oxidation-dissolution" process is repeated cyclically, with the first oxidant continuously dissolving the Fe... 2+ Oxidized to Fe 3+ Fe 3+ Continue to dissolve iron phosphide powder until the theoretically required amount of iron phosphide powder is completely dissolved, yielding a product rich in Fe. 2+ and PO4 3- The leachate.

[0038] S2: React at least a portion of the leachate with a second oxidizing agent to reduce the Fe in the leachate. 2+ All oxidized to Fe 3+ and PO4 3- Iron phosphate is produced.

[0039] That is, part of the leachate obtained in step S1 is used for subsequent oxidative synthesis of iron phosphate, and the other part is returned to step S1 as Fe. 2+ The source, mixed with newly added acid and iron phosphide powder, maintains the Fe content in the leaching system. 2+ The concentration is adjusted to achieve continuous leaching, forming a continuous and efficient closed-loop production process.

[0040] In some alternative embodiments, the remaining leachate, excluding the leachate returned to the leaching reaction apparatus, is subjected to solid-liquid separation, and the separated liquid is used to react with a second oxidant.

[0041] The leachate returned to the leaching reaction device is used as a circulating liquid to continue participating in the acidolysis process of iron phosphate powder, while the remaining leachate is used to prepare iron phosphate products in step S2 after solid-liquid separation.

[0042] In some optional embodiments, the volume percentage of the leachate used to react with the second oxidant can be 30% to 40% of the total leachate volume, such as 30%, 32%, 35%, 38%, or 40%, or other values ​​within the range of 30% to 40%. Furthermore, this percentage can also be adjusted based on the Fe content in the leaching system. 2+ The concentration needs to be kept stable and the product synthesis rate should be dynamically adjusted.

[0043] In some optional embodiments, the second oxidant may exemplary include at least one selected from oxygen, air, ozone, and hydrogen peroxide. In some preferred embodiments, the second oxidant may include at least one selected from oxygen and air. The actual amount of the second oxidant added may be 1 to 1.5 times the theoretical amount added, where the theoretical amount of the second oxidant refers to the amount of Fe... 2+ Completely formed Fe 3+ The required amount.

[0044] In some alternative embodiments, the leachate not used for reaction with the second oxidant is returned to a Fe-rich state. 2+ and PO4 3- In the leaching reaction apparatus of the leachate.

[0045] In some alternative embodiments, at least a portion of the leachate reacts with the second oxidant at a pH of 1.5 to 3.0 (e.g., 1.5, 1.8, 2.2, 2.5, 2.8, or 3) and a temperature of 50°C to 90°C (e.g., 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, or 90°C).

[0046] In some alternative implementations, the pH of the reaction can be adjusted by adding ammonia.

[0047] Continuing from the above, in step S2, the second oxidant reacts with the corresponding leachate, causing the Fe in that portion of the leachate to... 2+ All oxidized to Fe 3+ Fe 3+ With the PO4 in this part of the leachate 3- They combine to form iron phosphate.

[0048] Further, after step S2, solid-liquid separation is performed, and the separated solid is washed and dried to obtain battery-grade iron phosphate product.

[0049] In addition, the separated liquid can be recycled or discharged in compliance with standards after treatment.

[0050] Building upon the above, the method for preparing ferric phosphate based on continuous acid hydrolysis of ferric phosphate powder provided by this invention achieves efficient and continuous dissolution reaction of ferric phosphate by constructing an ingenious internal cyclic oxidation system for iron ions. This method is characterized by mild conditions, high efficiency, low cost, and ease of implementation.

[0051] Accordingly, the present invention also provides a system for the continuous acid hydrolysis of iron phosphide powder to prepare iron phosphate, including a leaching reaction apparatus and a product synthesis apparatus. Further, it may also include a solid-liquid separation apparatus and a diversion and circulation apparatus.

[0052] The leaching reaction apparatus is used to react a reaction slurry containing a solution of ferrous ions, acid, and iron phosphide powder with a first oxidant to obtain a Fe-rich solution. 2+ and PO4 3- The leachate.

[0053] The aforementioned leaching reaction apparatus includes at least one reactor for acid hydrolysis of iron phosphide powder. This reactor has a feed inlet, an oxidant inlet, and a discharge outlet. The feed inlet is used to add a ferrous ion solution, acid, and iron phosphide powder; the oxidant inlet is used to add a first oxidant; and the discharge outlet is used to discharge Fe-rich... 2+ and PO4 3- The leachate.

[0054] In some alternative embodiments, the dissolution reaction apparatus may include a stirred tank reactor, a tower reactor, or a cascade reactor group.

[0055] The diversion and circulation device is used to divert Fe-rich water... 2+ and PO4 3- The leachate is divided into a portion that returns to the leaching reaction unit and a portion that is used to enter the product synthesis unit, and the portion that returns to the leaching reaction unit is recycled back to the leaching reaction unit.

[0056] The solid-liquid separation device is used to separate the leachate from the second oxidant. The separated liquid is then used to react with the second oxidant. Specifically, the inlet of the diversion and circulation device is connected to the outlet of the leaching reaction device. The liquid separated by the diversion and circulation device is divided into circulating liquid and product liquid. The outlet of the diversion and circulation device is divided into a circulating liquid outlet and a product liquid outlet. The circulating liquid outlet is connected to the inlet of the leaching reaction device to return the circulating liquid to the Fe-rich area. 2+ and PO4 3- In the leaching reaction device of the leachate; the product liquid outlet is connected to the inlet of the solid-liquid separation device to perform solid-liquid separation of the product liquid, and the outlet of the solid-liquid separation device is connected to the inlet of the product synthesis device to transport the solid-liquid separated product liquid to the product synthesis device to react with the second oxidant.

[0057] The product synthesis apparatus is used to react at least a portion of the leachate (i.e., the product liquid after the aforementioned solid-liquid separation) with a second oxidant, so as to reduce the Fe in that portion of the leachate... 2+ All oxidized to Fe 3+ and PO4 3- Ferric phosphate is produced. The outlet of the product synthesis unit is then used to output ferric phosphate.

[0058] Furthermore, the above system can also be equipped with separation devices, washing devices, drying devices, etc., as needed, to prepare battery-grade iron phosphate products from the output of the product synthesis device.

[0059] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0060] The following examples all use industrial by-product iron phosphate powder (Fe2P) as raw material.

[0061] Example 1 This embodiment provides a method for preparing ferric phosphate based on continuous acid hydrolysis of ferric phosphate powder, including the following steps: S1: In a reactor equipped with heating and ventilation devices, add pure water to dissolve ferrous sulfate (FeSO4·7H2O) to prepare 10L of a 0.8mol / L ferrous ion solution. Add concentrated sulfuric acid to the reactor to adjust the acidity to 80g / L, and adjust the concentration of Fe in the ferrous ion solution according to the required concentration. 2+ An excess of iron phosphide powder (Fe₂P) was added at a molar ratio of 9:4 to the iron phosphide powder. Stirring was started, and air was simultaneously introduced at a flow rate of 3 L / min to maintain the reaction temperature at 95°C. The air carried the Fe... 2+ Oxidized to Fe 3+ Fe 3+ It immediately undergoes a redox reaction with iron phosphate powder, converting the iron and phosphorus in the iron phosphate powder into Fe. 2+ and PO4 3- Form dissolution, while Fe 3+ It was reduced to Fe 2+ The system always maintains Fe 2+ State. Iron phosphide powder and sulfuric acid are continuously added to the reactor, while Fe-rich water is continuously drawn from the bottom of the reactor. 2+ and PO4 3- The leachate.

[0062] rich in Fe 2+ and PO4 3- The leachate is diverted through a diversion valve, with about 70% of the flow being returned to the reactor as a circulating liquid to continue participating in the acidolysis process of iron phosphate powder, and 30% of the flow being filtered. The filtrate is then transported to the synthesis reactor as the product liquid to prepare iron phosphate products.

[0063] S2: In the synthesis reactor, the product liquid is heated to 80°C, excess air is introduced, and the pH is slowly adjusted and maintained at around 2.0 with ammonia. After 4 hours of reaction, a large amount of white precipitate (ferric phosphate) is generated.

[0064] The resulting white precipitate was filtered, washed, and dried to obtain the ferric phosphate product.

[0065] According to the test, the main components of the iron phosphate product, by mass percentage, are as follows: Fe 36.8%, P 20.56%, S 0.0034%, Ca 0.0025%, Mg 0.0024%, Si 0.002%, Na 0.006%. The main content of the product complies with the standard HG / T4701-2021 "Iron Phosphate for Batteries", and the content of key impurity elements (Ca, Mg and Na) is low.

[0066] Example 2 This embodiment provides a method for preparing ferric phosphate based on continuous acid hydrolysis of ferric phosphate powder, including the following steps: S1: In a reactor equipped with heating and ventilation devices, add pure water to dissolve ferrous sulfate (FeSO4·7H2O) to prepare 10L of a 0.65mol / L ferrous ion solution. Add concentrated sulfuric acid to the reactor to adjust the acidity to 65g / L, and adjust the concentration of Fe in the ferrous ion solution according to the required concentration. 2+ An excess of iron phosphide powder (Fe₂P) was added at a molar ratio of 9:4 to the iron phosphide powder. Stirring was started, and air was simultaneously introduced at a flow rate of 2 L / min to maintain the reaction temperature at 80°C. The air carried the Fe... 2+ Oxidized to Fe 3+ Fe 3+ It immediately undergoes a redox reaction with iron phosphate powder, converting the iron and phosphorus in the iron phosphate powder into Fe. 2+ and PO4 3- Form dissolution, while Fe 3+ It was reduced to Fe 2+ The system always maintains Fe 2+ State. Iron phosphide powder and sulfuric acid are continuously added to the reactor, while Fe-rich water is continuously drawn from the bottom of the reactor. 2+ and PO4 3- The leachate.

[0067] rich in Fe 2+ and PO4 3- The leachate is diverted through a diversion valve, with about 60% of the flow being returned to the reactor as a circulating liquid to continue participating in the acidolysis process of iron phosphate powder, and 40% of the flow being filtered. The filtrate is then transported to the synthesis reactor as the product liquid to prepare iron phosphate products.

[0068] S2: In the synthesis reactor, the product liquid is heated to 75°C, excess air is introduced, and the pH is slowly adjusted and maintained at around 2.0 with ammonia. After 4 hours of reaction, a large amount of white precipitate (ferric phosphate) is generated.

[0069] The resulting white precipitate was filtered, washed, and dried to obtain the ferric phosphate product.

[0070] According to the test results, the main components of the iron phosphate product, by mass percentage, are as follows: Fe 35.6%, P 21.2%, S 0.004%, Ca 0.0021%, Mg 0.002%, Si 0.002%, Na 0.001%. The main contents of the product meet the standards, and the contents of key impurity elements are low.

[0071] Example 3 The difference between this embodiment and Embodiment 1 is that in S1, the Fe in the ferrous ion solution is... 2+ An excess of iron phosphate powder (Fe2P) is added at a molar ratio of 9:2 to iron phosphate powder.

[0072] Example 4 The difference between this embodiment and Example 1 is that in S1, the reaction is carried out under the conditions of pH 1.5 and temperature 70°C.

[0073] Example 5 The difference between this embodiment and embodiment 1 is that in S2, the reaction is carried out under the conditions of pH 1.5 and temperature 90°C.

[0074] Example 6 The difference between this embodiment and embodiment 1 is that in S2, the reaction is carried out under the conditions of pH 3.0 and temperature 50°C.

[0075] Example 7 This embodiment provides a system for the continuous acid hydrolysis of iron phosphate powder to prepare iron phosphate. The system includes a leaching reaction device, a solid-liquid separation device, a diversion and circulation device, a product synthesis device, a separation device, a washing device, and a drying device.

[0076] The leaching reaction apparatus is used to react a reaction slurry containing a solution of ferrous ions, acid, and iron phosphide powder with a first oxidizing agent to obtain a Fe-rich solution. 2+ and PO4 3- The leachate is obtained from the leaching process. The leaching reaction apparatus is a stirred tank reactor, equipped with a feed inlet, an oxidant inlet, and a discharge outlet. The feed inlet is used to add ferrous ion solution, acid, and iron phosphide powder; the oxidant inlet is used to add the first oxidant; and the discharge outlet is used to discharge the Fe-rich solution. 2+ and PO4 3- The leachate.

[0077] The diversion and circulation device is used to divert Fe-rich water... 2+ and PO4 3- The leachate is divided into a portion returned to the leaching reactor and a portion used to enter the product synthesis unit. The portion returned to the leaching reactor is then recycled back into the leaching reactor. A solid-liquid separation unit is used to separate the leachate from the second oxidant; the separated liquid is then used to react with the second oxidant.

[0078] The inlet of the diversion and circulation device is connected to the outlet of the leaching reaction device. The liquid separated by the diversion and circulation device is divided into circulating liquid and product liquid. The outlet of the diversion and circulation device is divided into a circulating liquid outlet and a product liquid outlet. The circulating liquid outlet is connected to the inlet of the leaching reaction device to return the circulating liquid to the Fe-rich area. 2+ and PO4 3- In the leaching reaction device of the leachate; the product liquid outlet is connected to the inlet of the solid-liquid separation device to perform solid-liquid separation of the product liquid, and the outlet of the solid-liquid separation device is connected to the inlet of the product synthesis device to transport the solid-liquid separated product liquid to the product synthesis device to react with the second oxidant.

[0079] The product synthesis apparatus is used to react at least a portion of the leachate (i.e., the product liquid after the aforementioned solid-liquid separation) with a second oxidant, so as to reduce the Fe in that portion of the leachate... 2+ All oxidized to Fe 3+ and PO4 3- Ferric phosphate is produced. The outlet of the product synthesis unit is then used to output ferric phosphate.

[0080] The inlet of the separation device is connected to the outlet of the product synthesis device to separate the product in the product synthesis device; the inlet of the washing device is connected to the outlet of the separation device to wash the solid separated by the separation device; the inlet of the drying device is connected to the outlet of the washing device to dry the washed solid to obtain battery-grade iron phosphate product.

[0081] Comparative Example This comparative example provides a method for preparing lithium iron phosphate using iron phosphate powder as a raw material, which includes the following steps: (1) Pretreatment and acid leaching of ferrophosphorus powder: 100g of ferrophosphorus powder was weighed and placed in a muffle furnace and calcined at 650℃ for 4h, so that the phosphorus and iron were oxidized to P2O5 and Fe2O3, respectively. The calcined product was cooled and ground into powder. The powder was then transferred to a reaction vessel, and 500mL of 2mol / L sulfuric acid solution was added. The mixture was stirred and leached at 90℃ for 2h. During this process, most of the Fe2O3 and P2O5 reacted with sulfuric acid to produce ferric sulfate and phosphoric acid.

[0082] (2) Purification and impurity removal of the solution: The above acid leaching slurry was filtered to obtain a solution containing Fe. 3+ PO4 3- and various impurity ions (such as Al) 3+ Cu 2+ The leachate of Fe (etc.). 3+ Hydrolysis and precipitation begin at a pH of approximately 2.5, making it impossible to remove impurities simply by adjusting the pH. Therefore, the pH of the leachate was first adjusted to 4.0 using NaOH solution to allow Fe to precipitate. 3+ And Al 3+ These ions, along with other metal ions, form hydroxide precipitates, while phosphate ions react with some metal ions to form complex phosphate precipitates, resulting in phosphorus loss. Filtration yields impure iron-rich slag and a phosphorus-containing filtrate (requiring further treatment to recover phosphorus).

[0083] The iron-rich slag was redissolved with dilute sulfuric acid, and then NaOH solution was slowly added to the solution, strictly controlling the pH to around 3.0, for Fe... 3+ Hydrolysis precipitation, while Al 3+ The precipitate remains in the solution. After filtration and washing, a preliminarily purified ferric hydroxide precipitate is obtained. This precipitate is then dissolved again with sulfuric acid to prepare a ferric sulfate solution of higher purity.

[0084] (3) Synthesis of ferric phosphate: The purified ferric sulfate solution obtained in step (2) was mixed with the phosphorus-containing filtrate (after composition adjustment) at a 1:1 molar ratio of iron to phosphorus. The pH of the mixed solution was adjusted to 1.8 with ammonia, and the mixture was stirred and aged at 85°C for 2 hours to generate ferric phosphate precipitate. After the reaction was completed, the precipitate was filtered, washed repeatedly with deionized water, and dried at 110°C for 12 hours to obtain the precursor ferric phosphate.

[0085] Test case The utilization rates and yields of P and Fe elements corresponding to the methods provided in Examples 1-6 and the comparative examples were compared, and the results are shown in Table 1.

[0086] Table 1 Results

[0087] As can be seen from Table 1, the methods provided in Examples 1 to 6 of this invention can all achieve high utilization rates and yields of P and Fe elements.

[0088] Compared to the embodiments, the comparative method is lengthy, involving high-temperature roasting, multiple acid dissolutions, multiple precipitations, and filtrations. The operation is cumbersome, the production cycle is long, resulting in high energy consumption, large equipment investment, and high labor costs. Furthermore, the material yield of the entire process is reduced due to the multiple transfer steps. During the purification and impurity removal process in step (2), iron and phosphorus are severely lost. When the pH is initially adjusted to 4.0, phosphate ions co-precipitate with some metal impurities, leading to a low phosphorus recovery rate. The multiple precipitation-dissolution processes of iron also result in unavoidable losses. Moreover, the comparative method consumes a large amount of sulfuric acid and NaOH for pH adjustment and precipitation, generating a large amount of wastewater with high salinity, resulting in high subsequent treatment costs and a heavy environmental burden.

[0089] Therefore, compared with the traditional methods of comparison, the short-process technology based on the divalent iron cycle provided by the present invention has significant advantages in terms of production efficiency, raw material utilization, cost control and environmental friendliness, which fully demonstrates the progressiveness of the process of the present invention.

[0090] In summary, this invention ingeniously utilizes the principle of ferric phosphate oxidation to dissolve iron phosphate. By introducing a ferrous phosphate recycling system, it transforms iron phosphate, which is difficult to dissolve directly with acid, into a form that can be efficiently and completely dissolved, thus solving a technical bottleneck in the industry. This method constructs an internally circulating ferrous ion catalyst or oxygen carrier system by partially returning the leachate, allowing for continuous feeding of acid, iron phosphate powder, and oxidant, and continuous production of the leachate, greatly improving production efficiency and making it suitable for large-scale industrial production. Furthermore, the entire reaction is carried out at atmospheric pressure and moderate temperature, without the need for high-temperature calcination; the entire process does not use strong oxidants such as nitric acid, and does not produce toxic or harmful gases, making the process clean and environmentally friendly. In addition, the method provided by this invention fully utilizes the iron and phosphorus elements in the iron phosphate powder itself, resulting in a short process flow, low reagent consumption, high raw material utilization, and low overall production cost. Because impurities (such as metallic impurities) in the iron phosphate powder are not easily introduced into the solution or separated in subsequent synthesis under specific redox potentials, the high purity of the iron phosphate product is ensured.

[0091] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing ferric phosphate based on continuous acid hydrolysis of ferric phosphate powder, characterized in that, Includes the following steps: A first oxidizing agent is added to a reaction slurry containing a solution of ferrous ions, an acid, and iron phosphide powder to oxidize the Fe in the reaction slurry. 2+ Oxidized to Fe 3+ and the generated Fe 3+ The iron phosphate powder undergoes a redox reaction to obtain a product rich in Fe. 2+ and PO4 3- The leachate; At least a portion of the leachate is reacted with a second oxidant to reduce the Fe in the leachate. 2+ All oxidized to Fe 3+ and PO4 3- Iron phosphate is produced; Continuous application to obtain Fe-rich 2+ and PO4 3- Iron phosphide powder and acid are added to the leaching reaction device of the leachate, while Fe-rich solutions are continuously drawn from the leaching reaction device. 2+ and PO4 3- The leaching solution is used to ensure that the system in the leaching reaction apparatus always maintains Fe... 2+ state; The first oxidant and the second oxidant independently include at least one of oxygen, air, ozone and hydrogen peroxide; The generated Fe 3+ The oxidation-reduction reaction with the iron phosphide powder is carried out under conditions of pH 1.5~2 and temperature 60℃~95℃.

2. The method according to claim 1, characterized in that, Fe in the divalent iron ion solution 2+ The molar ratio of the iron phosphate powder to the iron phosphate powder is 9:2 to 9:

5.

3. The method according to claim 1, characterized in that, The acid includes at least one of sulfuric acid and phosphoric acid.

4. The method according to claim 1, characterized in that, The first oxidant and the second oxidant independently include at least one of oxygen and air.

5. The method according to claim 1, characterized in that, By volume percentage, the volume of leachate used to react with the second oxidant accounts for 30% to 40% of the total volume of leachate.

6. The method according to claim 5, characterized in that, Leachate not used for reaction with the second oxidant is returned to a Fe-rich state. 2+ and PO4 3- In the leaching reaction apparatus of the leachate.

7. The method according to claim 1, characterized in that, It also includes solid-liquid separation of the remaining leachate except for the one returned to the leaching reaction device, and the separated liquid is used to react with the second oxidant.

8. The method according to claim 1, characterized in that, The pH value of the at least part of the leachate reacting with the second oxidant is 1.5 to 3.0, and the temperature is 50°C to 90°C.

9. The method according to claim 8, characterized in that, The pH of the reaction was adjusted by adding ammonia.

Images