A method of washing a ferric phosphate product

Abstract

This invention relates to a washing method for ferric phosphate products, belonging to the field of ferric phosphate product preparation technology, and includes the following steps: S1, First combined washing: The ferric phosphate material to be treated is immersed in water for incubation and washing at a temperature of 80-99°C. After the first incubation and washing time, the temperature is lowered to a second temperature, hydrochloric acid is added, and the pH is controlled at 1-2. Washing is performed at the second temperature for a second time, followed by solid-liquid separation to obtain first combined washed ferric phosphate; S2, Phosphoric acid washing: The first combined washed ferric phosphate is washed with a phosphoric acid washing solution with a pH of 0-2. Washing is performed at a third temperature for a third time, followed by solid-liquid separation to obtain phosphoric acid washed ferric phosphate, wherein the pH of the phosphoric acid washing solution is lower than the pH of the first combined washing; S3, Water washing: The phosphoric acid washed ferric phosphate is washed with water, followed by solid-liquid separation to obtain purified ferric phosphate. The processing method of this invention can achieve simple and effective removal of trace impurities in ferric phosphate products, optimizing the purity of ferric phosphate products.

Description

Technical Field

[0001] This invention relates to the field of ferric phosphate product preparation technology, and specifically to a washing method for ferric phosphate products. Background Technology

[0002] In recent years, the new energy industry has experienced rapid development, and lithium iron phosphate batteries, as a high-performance power battery, have become the preferred choice for new energy electric vehicles. Lithium iron phosphate cathode materials have advantages such as high specific capacity, long cycle life, and good safety. Meanwhile, the demand for iron phosphate, as a crucial material for synthesizing lithium iron phosphate, is also increasing daily.

[0003] Ferric phosphate is generally derived from the smelting of ferrophosphate ore. In recent years, with the development of the battery recycling industry, the preparation of ferric phosphate from ferrophosphate slag has become an important source of ferric phosphate. Due to the diversity, complexity, and instability of raw material composition, even after product washing processes, the content of one or more impurity elements in the finished ferric phosphate product still exceeds the standard, forming trace impurities that are stably present in the ferric phosphate product. These trace impurities are difficult to effectively remove through conventional washing methods, ultimately causing the entire batch of product to fail to meet customer requirements. This results in the need for either downgrading and reuse, investing heavily in complex reprocessing, or sacrificing recovery rates to achieve a certain degree of purity improvement. However, regardless of the method used, it leads to a significant reduction in the overall value of ferric phosphate product recycling. Given the current surge in demand for high-quality ferric phosphate products, it is essential to develop low-cost technologies that can comprehensively and thoroughly reduce the content of various impurity elements, including trace impurities, in ferric phosphate products, thereby ensuring that the content of single or total impurities in ferric phosphate products remains at a low level. This can greatly reduce resource waste and production costs, and achieve sustainable, high-value recycling of resources.

[0004] Currently, there is little in-depth research on reducing trace impurities in ferric phosphate products. Only some existing technologies touch upon this topic. For example, patent CN 202311126858.8 discloses a method for preparing high-purity ferric phosphate material from ferric phosphate slag. This method involves treating the ferric phosphate slag to obtain crude ferric phosphate product, then using a first-type acid to acid-wash the crude ferric phosphate to remove phosphate impurities, thus obtaining high-purity ferric phosphate material. The first-type acid is selected from one or more of sulfuric acid, hydrochloric acid, oxalic acid, carbonic acid, citric acid, hydrofluoric acid, malic acid, gluconic acid, formic acid, lactic acid, benzoic acid, acrylic acid, acetic acid, propionic acid, stearic acid, hypochlorous acid, and nitric acid, with a concentration of 1%-20%. This process using the first-type acid can only remove phosphate impurities from the crude ferric phosphate and does not address the problem of residual trace impurities that are difficult to treat in ferric phosphate. The purity of the obtained ferric phosphate material can only reach above 98%, which cannot meet the purity requirements of high-quality ferric phosphate products.

[0005] Patent CN 202211734129.6 discloses a method for recovering ferric phosphate and lithium carbonate from waste materials. The method uses waste containing ferric phosphate, lithium carbonate, and glucose as raw materials. The process involves acid washing to obtain crude ferric phosphate and a lithium-containing solution. The crude ferric phosphate is then washed with water to obtain ferric phosphate. During washing, the mass ratio of crude ferric phosphate to water is 1:(5-20), the number of washes is 1-5, and the washing temperature is 90-98℃. This method can only process ferric phosphate recovered from specific ferric phosphate raw materials. Furthermore, the washing is mainly used to remove residual glucose from the raw materials, and it does not address the removal of difficult-to-treat trace impurities. The overall washing temperature is also relatively high, resulting in high energy consumption and significant safety hazards in the operating environment.

[0006] Patent CN 202011326398.X discloses a comprehensive recycling method for waste lithium iron phosphate batteries. Using waste lithium-ion batteries as raw materials, after selective lithium extraction, crude iron phosphate is prepared from the lithium extraction residue. This crude iron phosphate is then purified through a reverse three-stage washing process to obtain battery-grade iron phosphate. The reverse three-stage washing process includes the following steps: b1) Washing solution preparation: Superior purity hydrochloric acid is added to pure water to prepare a hydrochloric acid washing solution with a pH of 1.5-2.0 for later use; b2) First washing: The crude iron phosphate filter cake is added to the second washing water at a mass ratio of 1 / 3-5, stirred for 30-60 minutes, filtered by pressure, and washed with the second washing water. The filtrate and washing solution are then separated. Upon entering the wastewater treatment plant, the filter cake undergoes a second washing; b3) Second washing: The crude ferric phosphate filter cake obtained from the first washing is added to the third washing water at a mass ratio of 1 / 3-5, stirred for 30-60 minutes, filtered by pressure, and washed with the third washing water. The filtrate and washing liquid are used for the first washing; the filter cake then undergoes a third washing; b4) Third washing: The crude ferric phosphate filter cake obtained from the second washing is added to the prepared hydrochloric acid washing solution with a mass ratio of 1 / 3-5, stirred for 30-60 minutes, filtered by pressure, and washed with the prepared hydrochloric acid washing solution with a mass ratio of 1.5-2.0. The filtrate and washing liquid are used for the second washing. This process obtains crude ferric phosphate through alkali precipitation. It is difficult to obtain a product with the required phosphorus-to-ferric ratio by simply performing a three-stage reverse washing with hydrochloric acid. As can be seen from its examples and comparative examples, the pH range of acid washing is extremely narrow, making precise control in production operations difficult. The washing temperature is not disclosed, making it difficult to know the specific washing scheme and reproduce the washing effect. With only hydrochloric acid washing, it is difficult to avoid residual acid entrainment in the ferric phosphate product, and it only focuses on the removal of a small amount of impurities.

[0007] Patent CN 202210179731.1 discloses a method for producing battery-grade iron phosphate from iron-containing waste residue. Using iron-containing waste residue as raw material, fine-particle iron phosphate is obtained through ammonium phosphate precipitation, followed by washing and drying to obtain battery-grade iron phosphate. In this patent, the fine-particle iron phosphate is washed once with a freshly prepared 0.1 mol / L phosphoric acid solution, filtered, and then washed twice with water. This patent also suffers from the drawbacks of direct acid washing resulting in significant iron phosphate dissolution loss, high requirements for the washing solution (requiring freshly prepared solution), and complex reagent preparation. Furthermore, its washing method is also insufficient to remove trace impurities.

[0008] In addition, the current process involves too many washes, which is a crude washing method that sacrifices washing efficiency and loss rate to obtain qualified products. This not only wastes resources and manpower, but also makes it difficult to guarantee the washing effect. Summary of the Invention

[0009] The present invention provides a washing method for ferric phosphate products to solve at least one of the technical problems mentioned in the background art.

[0010] The technical solution of this invention is as follows: A washing method for ferric phosphate products includes the following steps: S1. One-time combined washing: The ferric phosphate material to be treated is put into water for heat preservation and washing at a temperature of 80-99℃. After the first heat preservation and washing time, the temperature is lowered to the second temperature, hydrochloric acid is added, and the pH is controlled at 1-2. The material is washed for the second time at the second temperature, and the solid and liquid are separated to obtain ferric phosphate that has been washed once. S2, Phosphoric acid washing: The first combined washing of ferric phosphate is washed with a phosphoric acid washing solution with a pH of 0-2, and then washed for a third time at a third washing temperature. Solid-liquid separation is performed to obtain phosphoric acid washed ferric phosphate, wherein the pH of the phosphoric acid washing solution is lower than the pH of the first combined washing. S3. Water washing: Wash the ferric phosphate with the phosphoric acid, and separate the solid and liquid to obtain purified ferric phosphate.

[0011] Furthermore, in S1, the heat preservation washing temperature is 80-95℃, preferably 85-95℃, and more preferably 85-90℃.

[0012] Furthermore, in S1, the concentration of hydrochloric acid used is ≥1 mol / L, preferably ≥2 mol / L, and more preferably ≥3 mol / L.

[0013] Furthermore, in S1, the amount of iron phosphate added satisfies a liquid-to-solid ratio (mass ratio, the same below) of 4-6:1, preferably 4.5-6:1, and more preferably 4.5-5.5:1.

[0014] Furthermore, in S1, the first time for heat preservation and washing is 60-180 minutes, preferably 90-150 minutes, and more preferably 120-150 minutes.

[0015] Furthermore, in S1, the pH is controlled at 1.1-1.9, preferably 1.2-1.8, and more preferably 1.3-1.7.

[0016] Furthermore, in S1, the second temperature is 40-80°C, preferably 45-70°C, and more preferably 50-60°C.

[0017] Furthermore, in S1, the second time is 15-60 min, preferably 20-50 min, and more preferably 25-45 min.

[0018] Furthermore, in S1, when the temperature drops to the second temperature, the temperature drop is greater than 10°C.

[0019] Furthermore, in S2, the pH of the phosphoric acid washing solution is 0.1-2, preferably 0.1-1.5, and more preferably 0.1-1.

[0020] Furthermore, in S2, the third washing temperature is 50-90°C, preferably 55-80°C, and more preferably 60-75°C.

[0021] Furthermore, in S2, the washing liquid to solid ratio is 3-5:1, preferably 3.5-4.5:1, and more preferably 4-5:1.

[0022] Furthermore, in S2, the third time is 15-60 min, preferably 20-50 min, and more preferably 25-40 min.

[0023] Furthermore, in S3, the water washing temperature is 40-80℃, preferably 45-70℃, and more preferably 50-65℃.

[0024] Furthermore, in S3, the washing liquid to solid ratio is 3-8:1, preferably 3-6:1, and more preferably 4-6:1.

[0025] Furthermore, in the water washing step, the washing time is 10-60 minutes, preferably 12-45 minutes, and more preferably 15-30 minutes.

[0026] Furthermore, it also includes: S4, drying step, in which the purified ferric phosphate product obtained from the water washing step is dried to obtain the ferric phosphate product.

[0027] Furthermore, the content of ferric phosphate or ferric phosphate dihydrate in the anhydrous ferric phosphate material to be treated is 99.0 wt.% or more, preferably 99.5% or more, and more preferably 99.9% or more.

[0028] This invention optimizes the washing process of ferric phosphate by employing a single combined washing, followed by sequential washing with phosphoric acid and water. This approach further enhances the purity of ferric phosphate products, effectively removing not only conventional impurities but also trace impurities that cannot be removed by conventional single acid washing and / or water washing. Furthermore, it reduces the number of washing cycles, improving washing efficiency, minimizing water waste, and effectively avoiding additional losses caused by multiple solid-liquid separations during production line operations. Specifically, the single combined washing process involves high-temperature water washing to pre-wash soluble impurities and stabilize the ferric phosphate structure, reducing dissolution losses during subsequent acid washing. Following the high-temperature water washing, hydrochloric acid washing removes trace impurities that are difficult to remove effectively with water alone. Then, washing with a lower pH phosphoric acid solution further removes impurities and replaces other forms of iron salts, such as ferric hydroxide, in the ferric phosphate product, improving the purity of the ferric phosphate material and optimizing the phosphorus-to-iron ratio. Finally, pure water washing removes residual acid and further eliminates any remaining trace impurities. By organically combining the steps, trace impurities that are difficult to remove with conventional washing are effectively removed, while avoiding uncontrollable losses caused by the dissolution of iron phosphate, thus ensuring the recovery rate of iron phosphate products. Through the organic combination of washing steps and the control of relevant parameters between steps, trace impurities in lithium iron phosphate products are effectively removed, achieving high-value recycling and regeneration of iron phosphate products.

[0029] Beneficial effects (1) The process has high applicability and is applicable to ferric phosphate products containing trace impurities prepared by various wet processes, and has high industrial application value.

[0030] (2) In response to the problem that trace impurities in battery-grade iron phosphate exceed the standard and are difficult to remove to the level required by customers, the present invention can effectively remove them, ensuring that the overall purity of the product and the content of a single impurity meet the requirements. Moreover, there are no restrictions on iron phosphate raw materials or pre-preparation processes. Therefore, there is no need to modify the existing production line, nor is there any need to worry about the adverse effects of the diversity and complexity of raw materials on the final product.

[0031] (3) On the basis of improving product purity, the loss caused by the dissolution of ferric phosphate during the washing process is effectively avoided, the final product yield is guaranteed, and the economic benefits are guaranteed.

[0032] (4) Fewer washing cycles effectively reduce washing water consumption, avoiding washing water treatment problems from the source. At the same time, reducing the number of filtration cycles can effectively improve production efficiency and reduce additional losses caused by filtration operations. Implementation The present invention will be described in detail below with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other. Unless otherwise specified, the relevant percentages refer to mass percentages. The ferric phosphate raw material compositions in the embodiments and comparative examples of this application are merely exemplary components and do not constitute a limitation on the processing of ferric phosphate materials in this application.

[0033] The main components of the ferric phosphate raw material before washing in the following examples are as follows: Example 1 The ferric phosphate material to be treated was immersed in water at 90°C and washed for 120 min at a liquid-to-solid mass ratio of 5:1. The temperature was then lowered to 60°C, hydrochloric acid was added to adjust the pH to 2, and the mixture was washed for another 30 min. Solid-liquid separation was then performed to obtain first-stage washed ferric phosphate. The first-stage washed ferric phosphate was then washed with a phosphoric acid washing solution at pH 0.5 at 80°C and a liquid-to-solid ratio of 4:1 for 30 min, followed by solid-liquid separation to obtain phosphoric acid washed ferric phosphate. Finally, the phosphoric acid washed ferric phosphate was washed with water at a liquid-to-solid ratio of 4:1 at 60°C for 30 min, followed by solid-liquid separation to obtain purified ferric phosphate. In this embodiment, the ferric phosphate loss rate was 5.21%.

[0034] The composition of the washed ferric phosphate product is as follows: Example 2 The ferric phosphate material to be treated was immersed in water at 80°C and washed for 60 minutes at a liquid-to-solid mass ratio of 6:1. The temperature was then lowered to 70°C, and hydrochloric acid was added to adjust the pH to 1.5. After washing for another 30 minutes, solid-liquid separation was performed to obtain first-stage washed ferric phosphate. The first-stage washed ferric phosphate was then washed with a phosphoric acid washing solution at pH 0.1 at 65°C and a liquid-to-solid ratio of 5:1 for 20 minutes, followed by solid-liquid separation to obtain phosphoric acid washed ferric phosphate. Finally, the phosphoric acid washed ferric phosphate was washed with water at a liquid-to-solid ratio of 5:1 at 50°C for 30 minutes, followed by solid-liquid separation to obtain purified ferric phosphate. In this example, the ferric phosphate loss rate was 8.34%.

[0035] The composition of the washed ferric phosphate product is as follows: Example 3 The ferric phosphate material to be treated was immersed in water at 95°C and washed for 90 minutes at a liquid-to-solid mass ratio of 4:1. The temperature was then lowered to 45°C, and hydrochloric acid was added to adjust the pH to 1.0. After washing for 20 minutes, solid-liquid separation was performed to obtain first-stage washed ferric phosphate. The first-stage washed ferric phosphate was then washed with a phosphoric acid washing solution at pH 0.4 at 90°C and a liquid-to-solid ratio of 3:1 for 25 minutes, followed by solid-liquid separation to obtain phosphoric acid washed ferric phosphate. Finally, the phosphoric acid washed ferric phosphate was washed with water at a liquid-to-solid ratio of 3:1 at 70°C for 25 minutes, followed by solid-liquid separation to obtain purified ferric phosphate. In this example, the ferric phosphate loss rate was 7.53%.

[0036] The composition of the washed ferric phosphate product is as follows: Example 4 The ferric phosphate material to be treated was immersed in water at 85°C and washed for 150 min at a liquid-to-solid mass ratio of 5:1. The temperature was then lowered to 50°C, and hydrochloric acid was added to adjust the pH to 1.2. After washing for 45 min, solid-liquid separation was performed to obtain first-stage washed ferric phosphate. The first-stage washed ferric phosphate was then washed with a phosphoric acid washing solution at pH 0.9 at 70°C and a liquid-to-solid ratio of 3:1 for 45 min, followed by solid-liquid separation to obtain phosphoric acid washed ferric phosphate. Finally, the phosphoric acid washed ferric phosphate was washed with water at a liquid-to-solid ratio of 4:1 at 45°C for 35 min, followed by solid-liquid separation to obtain purified ferric phosphate. In this example, the ferric phosphate loss rate was 6.75%.

[0037] The composition of the washed ferric phosphate product is as follows: Example 5 The ferric phosphate material to be treated was immersed in water at 99°C and washed for 180 min at a liquid-to-solid mass ratio of 6:1. The temperature was then lowered to 75°C, and hydrochloric acid was added to adjust the pH to 1.8. After washing for 60 min, solid-liquid separation was performed to obtain first-stage washed ferric phosphate. The first-stage washed ferric phosphate was then washed with a phosphoric acid washing solution at pH 1.5 at 60°C and a liquid-to-solid ratio of 4:1 for 60 min, followed by solid-liquid separation to obtain phosphoric acid washed ferric phosphate. Finally, the phosphoric acid washed ferric phosphate was washed with water at a liquid-to-solid ratio of 5:1 at 40°C for 15 min, followed by solid-liquid separation to obtain purified ferric phosphate. In this example, the ferric phosphate loss rate was 6.11%.

[0038] The composition of the washed ferric phosphate product is as follows: Comparative Example 1 The ferric phosphate material to be treated was immersed in water at 60°C and washed for 120 min at a liquid-to-solid mass ratio of 5:1. After cooling to 60°C, hydrochloric acid was added to adjust the pH to 2, and the mixture was washed for another 30 min, followed by solid-liquid separation to obtain first-stage washed ferric phosphate. The first-stage washed ferric phosphate was then washed with a phosphoric acid washing solution at pH 0.5 at 80°C and a liquid-to-solid ratio of 4:1 for 30 min, followed by solid-liquid separation to obtain phosphoric acid washed ferric phosphate. Finally, the phosphoric acid washed ferric phosphate was washed with water at a liquid-to-solid ratio of 4:1 at 60°C for 30 min, followed by solid-liquid separation to obtain purified ferric phosphate. In this example, the ferric phosphate loss rate was 19.48%.

[0039] The composition of the washed ferric phosphate product is as follows: Comparative Example 2 The ferric phosphate material to be treated was immersed in water at 90°C and washed for 120 min at a liquid-to-solid mass ratio of 5:1. The temperature was then raised to 95°C, hydrochloric acid was added to adjust the pH to 2, and the mixture was washed for another 30 min. Solid-liquid separation was then performed to obtain ferric phosphate washed once. The ferric phosphate was then washed with a phosphoric acid washing solution at pH 0.5 at 80°C and a liquid-to-solid ratio of 4:1 for 30 min, followed by solid-liquid separation to obtain phosphoric acid washed ferric phosphate. Finally, the phosphoric acid washed ferric phosphate was washed with water at a liquid-to-solid ratio of 4:1 at 60°C for 30 min, followed by solid-liquid separation to obtain purified ferric phosphate. In this example, the ferric phosphate loss rate was 15.71%.

[0040] The composition of the washed ferric phosphate product is as follows: Comparative Example 3 The ferric phosphate material to be treated was immersed in water at 90°C and washed for 120 min at a liquid-to-solid mass ratio of 2:1. The temperature was then lowered to 60°C, hydrochloric acid was added to adjust the pH to 2, and the mixture was washed for another 30 min. Solid-liquid separation was then performed to obtain ferric phosphate washed once. The ferric phosphate was then washed with a phosphoric acid washing solution at pH 0.5 at 80°C and a liquid-to-solid ratio of 2:1 for 30 min, followed by solid-liquid separation to obtain phosphoric acid washed ferric phosphate. Finally, the phosphoric acid washed ferric phosphate was washed with water at a liquid-to-solid ratio of 2:1 at 60°C for 30 min, followed by solid-liquid separation to obtain purified ferric phosphate. In this embodiment, the ferric phosphate loss rate was 4.26%.

[0041] The composition of the washed ferric phosphate product is as follows: Comparative Example 4 The ferric phosphate material to be treated was immersed in water at 90°C and washed for 120 min at a liquid-to-solid mass ratio of 8:1. The temperature was then lowered to 60°C, hydrochloric acid was added to adjust the pH to 2, and the mixture was washed for another 30 min. Solid-liquid separation was then performed to obtain ferric phosphate washed once. The ferric phosphate was then washed with a phosphoric acid washing solution at pH 0.5 at 80°C and a liquid-to-solid ratio of 8:1 for 30 min, followed by solid-liquid separation to obtain phosphoric acid washed ferric phosphate. Finally, the phosphoric acid washed ferric phosphate was washed with water at a liquid-to-solid ratio of 8:1 at 60°C for 30 min, followed by solid-liquid separation to obtain purified ferric phosphate. In this example, the ferric phosphate loss rate was 16.11%.

[0042] The composition of the washed ferric phosphate product is as follows: Comparative Example 5 The ferric phosphate material to be treated was immersed in water at 90°C and washed for 120 min at a liquid-to-solid mass ratio of 5:1. The temperature was then lowered to 60°C, hydrochloric acid was added to adjust the pH to 2, and the material was washed for another 5 min. Solid-liquid separation was then performed to obtain ferric phosphate washed once. The ferric phosphate was then washed with a phosphoric acid washing solution at pH 0.5 at 80°C and a liquid-to-solid ratio of 4:1 for 5 min, followed by solid-liquid separation to obtain phosphoric acid washed ferric phosphate. Finally, the phosphoric acid washed ferric phosphate was washed with water at a liquid-to-solid ratio of 4:1 at 60°C for 30 min, followed by solid-liquid separation to obtain purified ferric phosphate. In this embodiment, the ferric phosphate loss rate was 3.37%.

[0043] The composition of the washed ferric phosphate product is as follows: Comparative Example 6 The ferric phosphate material to be treated was immersed in water at 90°C and washed for 120 minutes at a liquid-to-solid mass ratio of 5:1. The temperature was then lowered to 60°C, hydrochloric acid was added to adjust the pH to 2, and the mixture was washed for another 90 minutes. Solid-liquid separation was then performed to obtain first-stage washed ferric phosphate. The first-stage washed ferric phosphate was then washed with a phosphoric acid washing solution at pH 0.5 at 80°C and a liquid-to-solid ratio of 4:1 for 30 minutes, followed by solid-liquid separation to obtain phosphoric acid washed ferric phosphate. Finally, the phosphoric acid washed ferric phosphate was washed with water at a liquid-to-solid ratio of 4:1 at 60°C for 30 minutes, followed by solid-liquid separation to obtain purified ferric phosphate. In this example, the ferric phosphate loss rate was 13.53%.

[0044] The composition of the washed ferric phosphate product is as follows: Comparative Example 7 The ferric phosphate material to be treated was immersed in water at 60°C and washed for 120 min at a liquid-to-solid mass ratio of 5:1, followed by solid-liquid separation to obtain once-washed ferric phosphate. The once-washed ferric phosphate was then washed with a phosphoric acid washing solution at pH 0.5 at 80°C and a liquid-to-solid ratio of 4:1 for 30 min, followed by solid-liquid separation to obtain phosphoric acid-washed ferric phosphate. Finally, the phosphoric acid-washed ferric phosphate was washed with water at 60°C and a liquid-to-solid ratio of 4:1 for 30 min, followed by solid-liquid separation to obtain purified ferric phosphate. In this embodiment, the ferric phosphate loss rate was 3.79%.

[0045] The composition of the washed ferric phosphate product is as follows: Comparative Example 8 The ferric phosphate material to be treated was immersed in water at 60°C at a liquid-to-solid mass ratio of 5:1 and washed for 120 minutes. After cooling to 60°C, hydrochloric acid was added to adjust the pH to 2, and the mixture was washed for another 30 minutes. Solid-liquid separation was then performed to obtain ferric phosphate that had undergone a single combined washing process. This ferric phosphate was then washed with water at a liquid-to-solid ratio of 4:1 at 60°C for 30 minutes, followed by solid-liquid separation to obtain purified ferric phosphate. In this embodiment, the ferric phosphate loss rate was 4.96%.

[0046] The composition of the washed ferric phosphate product is as follows: Comparative Example 9 The ferric phosphate material to be treated was immersed in water at 90°C and washed for 120 minutes at a liquid-to-solid ratio of 5:1. The temperature was then lowered to 60°C, and the material was washed for another 30 minutes, followed by solid-liquid separation to obtain first-washed ferric phosphate. The first-washed ferric phosphate was then washed with water at 80°C and a liquid-to-solid ratio of 4:1 for 30 minutes, followed by solid-liquid separation to obtain second-washed ferric phosphate. Finally, the ferric phosphate was washed with phosphoric acid at a liquid-to-solid ratio of 4:1 at 60°C for 30 minutes, followed by solid-liquid separation to obtain purified ferric phosphate. In this embodiment, the ferric phosphate loss rate was 2.13%.

[0047] Comparative Example 10 The ferric phosphate material to be treated was immersed in water at 90°C and washed for 120 min at a liquid-to-solid mass ratio of 5:1. The temperature was then lowered to 60°C, and phosphoric acid was added to adjust the pH to 0.5. After washing for 30 min, solid-liquid separation was performed to obtain first-stage washed ferric phosphate. The first-stage washed ferric phosphate was then washed with hydrochloric acid solution at pH 2 at 80°C and a liquid-to-solid ratio of 4:1 for 30 min, followed by solid-liquid separation to obtain hydrochloric acid washed ferric phosphate. Finally, the phosphoric acid washed ferric phosphate was washed with water at a liquid-to-solid ratio of 4:1 at 60°C for 30 min, followed by solid-liquid separation to obtain purified ferric phosphate. In this example, the ferric phosphate loss rate was 5.07%.

[0048] The composition of the washed ferric phosphate product is as follows: As can be seen from the above examples and comparative examples, washing with hydrochloric acid, phosphoric acid, and water alone, or washing with phosphoric acid first and then hydrochloric acid, cannot effectively remove trace impurities while ensuring that the phosphorus-to-iron ratio of the product meets the national standard requirements. In contrast, water pretreatment in a single combined washing process plays an important role in stabilizing ferric phosphate and reducing the loss of ferric phosphate during the washing process.

[0049] The above embodiments should be understood as being used only to illustrate the present invention more clearly, and not to limit the scope of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art fall within the scope defined by the appended claims.

Claims

1. A washing method for ferric phosphate products, characterized in that, Includes the following steps: S1. Single-stage combined washing: The ferric phosphate material to be treated is immersed in water for incubation and washing at a temperature of 80-99℃. After the first incubation and washing time, the temperature is lowered to a second temperature, hydrochloric acid is added, and the pH is controlled at 1-2. The material is then washed at the second temperature for a second time, resulting in solid-liquid separation and obtaining single-stage combined-washed ferric phosphate. The amount of ferric phosphate added meets the requirement of a liquid-to-solid ratio of 4-6:

1. The first incubation and washing time is 60-180 min. The second temperature is 40-80℃. The second washing time is 15-60 min. S2, Phosphoric acid washing: The first combined washing of ferric phosphate is washed with a phosphoric acid washing solution with a pH of 0-2, and then washed for a third time at a third washing temperature. Solid-liquid separation is performed to obtain phosphoric acid washed ferric phosphate, wherein the pH of the phosphoric acid washing solution is lower than the pH of the first combined washing. S3. Water washing: Wash the ferric phosphate with the phosphoric acid, and separate the solid and liquid to obtain purified ferric phosphate.

2. The washing method for ferric phosphate products according to claim 1, characterized in that, In step S1, the heat preservation and washing temperature is 80-95℃.

3. The washing method for ferric phosphate products according to claim 1, characterized in that, In S1, the heat preservation and washing temperature is 85-95℃.

4. The washing method for the ferric phosphate product according to claim 1, characterized in that, In S1, the heat preservation and washing temperature is 85-90℃.

5. The washing method for the ferric phosphate product according to any one of claims 1-4, characterized in that, In S1, the concentration of hydrochloric acid used is ≥1 mol / L.

6. The washing method for the ferric phosphate product according to any one of claims 1-4, characterized in that, In S1, the concentration of hydrochloric acid used is ≥2mol / L.

7. The washing method for the ferric phosphate product according to any one of claims 1-4, characterized in that, In S1, the concentration of hydrochloric acid used is ≥3mol / L.

8. The washing method for the ferric phosphate product according to claim 1, characterized in that, In step S1, the amount of ferric phosphate added satisfies a liquid-to-solid ratio of 4.5-6:1; and / or the first washing time is 90-150 min.

9. The washing method for the ferric phosphate product according to claim 1, characterized in that, In step S1, the amount of ferric phosphate added satisfies a liquid-to-solid ratio of 4.5-5.5:1; and / or the first washing time is 120-150 min.

10. The washing method for the ferric phosphate product according to any one of claims 1-4, characterized in that, In S1, when the temperature drops to the second temperature, the temperature drop is greater than 10°C.

11. The washing method for the ferric phosphate product according to any one of claims 1-4, characterized in that, In S1, the pH is controlled to be 1.1-1.

9.

12. The washing method for the ferric phosphate product according to any one of claims 1-4, characterized in that, In S1, the pH is controlled at 1.2-1.8; and / or the second temperature is 45-70℃; and / or the second time is 20-50min.

13. The washing method for the ferric phosphate product according to any one of claims 1-4, characterized in that, In S1, the pH is controlled at 1.3-1.7; and / or the second temperature is 50-60℃; and / or the second time is 25-45min.

14. The washing method for the ferric phosphate product according to any one of claims 1-4, characterized in that, In step S2, the pH of the phosphoric acid washing solution is 0.1-2; and / or the third washing temperature is 50-90℃; and / or the washing solution-to-solid ratio is 3-5:1; and / or the third washing time is 15-60 min.

15. The washing method for the ferric phosphate product according to any one of claims 1-4, characterized in that, In step S2, the pH of the phosphoric acid washing solution is 0.1-1.5; and / or the third washing temperature is 55-80℃; and / or the washing solution-to-solid ratio is 3.5-4.5:1; and / or the third washing time is 20-50 min.

16. The washing method for the ferric phosphate product according to any one of claims 1-4, characterized in that, In step S2, the pH of the phosphoric acid washing solution is 0.1-1; and / or the third washing temperature is 60-75℃; and / or the washing solution-to-solid ratio is 4-5:1; and / or the third washing time is 25-40 min.

17. The washing method for the ferric phosphate product according to any one of claims 1-4, characterized in that, In step S3, the water washing temperature is 40-80℃; and / or the washing liquid-to-solid ratio is 3-8:1; and / or the washing time is 10-60 min.

18. The washing method for the ferric phosphate product according to any one of claims 1-4, characterized in that, In step S3, the water washing temperature is 45-70℃; and / or the washing liquid-to-solid ratio is 3-6:1; and / or the washing time is 12-45 min.

19. The washing method for the ferric phosphate product according to any one of claims 1-4, characterized in that, In step S3, the water washing temperature is 50-65℃; and / or the washing liquid-to-solid ratio is 4-6:1; and / or the washing time is 15-30 min.

20. The washing method for the ferric phosphate product according to any one of claims 1-4, characterized in that, Also includes: S4. Drying step: The purified ferric phosphate product obtained from the water washing step is dried to obtain the dried ferric phosphate product.

21. The washing method for the ferric phosphate product according to any one of claims 1-4, characterized in that, The iron phosphate material to be treated contains 99.0 wt.% or more of iron phosphate or iron phosphate dihydrate.

22. The washing method for the ferric phosphate product according to any one of claims 1-4, characterized in that, The iron phosphate material to be treated contains 99.5 wt.% or more of iron phosphate or iron phosphate dihydrate.

23. The washing method for the ferric phosphate product according to any one of claims 1-4, characterized in that, The iron phosphate material to be treated contains 99.9 wt.% or more of iron phosphate or iron phosphate dihydrate.

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