Synthesis method of high-purity ferrous chloride

Abstract

The invention discloses a synthetic method of high-purity ferrous chloride. The synthetic method comprises the following steps: S1, adding iron powder into iron-containing hydrochloric acid for reduction treatment; s2, carrying out filter pressing to remove insoluble impurities; s3, performing efficient concentration treatment to extract ferrous chloride tetrahydrate crystals; s4, obtaining a metal oxide with a high melting point through a two-stage mild heating process; s5, adding an iron reducing agent, and carrying out uniform mixing and fine ball milling treatment; s6, putting in a high-temperature sintering furnace, and reducing residual ferric ions into ferrous ions; and S7, obtaining anhydrous ferrous chloride with high purity and high crystallinity. Compared with the prior art, the method disclosed by the invention is simple in principle, easily available in raw materials, low in cost and easy for mass production, and the residual hydroxide is ingeniously converted into the high-melting-point oxide in the water removal link, so that the iron oxyhydroxide is thoroughly removed, the content of impurities such as hydroxyl and ferric ions is remarkably reduced, and the method is suitable for industrial production. The chemical stability and the electrochemical performance of ferrous chloride are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of chemical engineering, and more particularly to a method for synthesizing high-purity ferrous chloride. Background Technology

[0002] The global energy structure transformation is accelerating, and battery technology, as a key component of clean energy storage, is of paramount importance. In recent years, liquid battery technology has made significant progress, with energy density approaching its theoretical limit, but further improvements face numerous challenges. This has prompted researchers to turn their attention to all-solid-state batteries, which are considered the most promising next-generation battery technology due to their advantages in higher safety, energy density, and cycle life. However, the development of all-solid-state batteries still faces many problems. Among them, poor interfacial compatibility between solid electrolytes and electrode materials, and low ion transport efficiency are key factors restricting their performance improvement. In particular, chloride-based all-solid-state batteries, while possessing high ionic conductivity and good electrochemical stability, suffer from particularly prominent interfacial compatibility issues with electrode materials.

[0003] Recent research has found that the introduction of ferrous chloride (FeCl2) offers a new approach to solving the aforementioned problems. Ferrous chloride not only significantly increases the battery's operating voltage but also enhances the compatibility between chloride electrolytes and electrode materials. The introduction of this material effectively improves interfacial stability and increases ion transport efficiency, thereby significantly improving the overall performance of all-solid-state batteries. Therefore, the application of ferrous chloride in the field of all-solid-state batteries has attracted widespread attention, providing a new direction for promoting the development of all-solid-state battery technology.

[0004] The traditional process for preparing ferrous chloride typically involves adding excess iron powder to hydrochloric acid of a certain concentration, followed by pressure filtration. The resulting filtrate is then concentrated under reduced pressure at 70-110°C to a specific gravity. After cooling and stirring, ferrous chloride crystals are crystallized, and finally, solid ferrous chloride is obtained by centrifugation. Although this process is relatively simple and low-cost, it has significant drawbacks.

[0005] First, this method is prone to introducing ferric hydroxy oxide impurities, which leads to a decrease in product purity.

[0006] Secondly, traditional processes make it difficult to precisely control the content of water of crystallization and oxygen at the same time, which directly affects the chemical stability and electrochemical performance of ferrous chloride.

[0007] In addition, impurity ions (such as Fe) 3+ OH - The presence of (etc.) will significantly affect the interfacial stability of ferrous chloride, thereby reducing its performance in all-solid-state batteries.

[0008] To avoid the introduction of ferric hydroxide impurities in traditional processes, anhydrous ferric chloride (FeCl3) can be synthesized by reacting iron with chlorine gas. This is followed by the introduction of dry, pure hydrogen gas and heating to 300-350°C for a reduction reaction to obtain anhydrous ferrous chloride. However, this method also suffers from unstable product purity, making it difficult to meet the requirements for high-purity materials. Summary of the Invention

[0009] The purpose of this invention is to provide a method for synthesizing high-purity ferrous chloride that solves the above-mentioned problems. Based on the traditional method for obtaining ferrous chloride, further processing can effectively control ferric hydroxide and impurity ions (such as Fe). 3+ OH - The content of (etc.) can be increased to improve its chemical stability and electrochemical performance.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is: a method for synthesizing high-purity ferrous chloride, the method steps of which are as follows:

[0011] S1: Iron-containing hydrochloric acid is transported to a stirring tank, and iron powder is added in proportion as a reducing agent to reduce the ferric ions to ferrous ions. In the stirring tank, the iron powder and iron-containing hydrochloric acid come into full contact and react chemically, which promotes the gradual reduction of the small amount of ferric ions in the solution to ferrous ions.

[0012] S2: The iron-containing hydrochloric acid that has undergone reduction treatment is filtered using a filter press to completely remove the insoluble impurities remaining in the solution;

[0013] S3: The clarified filtrate obtained after fine filtration is sent to the evaporation system for efficient concentration to extract ferrous chloride tetrahydrate crystals;

[0014] S4: Place the ferrous chloride tetrahydrate crystals into a vacuum tube furnace, start the vacuum system, and evacuate the furnace environment to a high vacuum state to ensure that the dehydration process is carried out in a low oxygen and low impurity environment. A two-stage mild heating process is used to promote the complete decomposition of the residual hydroxide at high temperature and transform it into a metal oxide with a high melting point.

[0015] S5: Accurately weigh the material obtained after step S4 and add an appropriate amount of iron reducing agent. Then, transfer the mixture to a ball mill under an argon atmosphere and start the ball mill for uniform mixing and fine ball milling.

[0016] Ball milling not only ensures uniform mixing of the material and the iron reducing agent, but also further refines the particles and enhances the reactivity, thereby ensuring a complete reaction. To improve the reactivity, the discharge particle size of the mixture is controlled at 1~20µm, preferably 1~10µm, and more preferably 1~5µm, because the smaller the particle size, the stronger the reactivity.

[0017] S6: The mixture after fine grinding in a ball mill is evenly filled into a pre-cleaned and dried quartz tube to ensure that the material is tightly packed and evenly distributed. Then, the quartz tube is placed in a special high-temperature sintering furnace to allow the material to fully react in a high-temperature environment and reduce the residual ferric ions to ferrous ions.

[0018] S7: After sintering, the quartz tube is transferred to a high-vacuum distillation system. By precisely controlling the distillation temperature and pressure, and utilizing the sublimation properties of ferrous chloride, it is efficiently separated from the mixture and collected by condensation. After this series of meticulous operations, a high-purity, highly crystalline anhydrous ferrous chloride product is finally obtained.

[0019] This invention employs an innovative technical solution, cleverly designing a process flow based on the characteristics of ferrous chloride tetrahydrate being easily decomposed, metal oxides having high melting and boiling points, and ferrous chloride being readily sublimable. First, low-temperature treatment under vacuum conditions promotes the decomposition of ferrous chloride tetrahydrate, generating anhydrous ferrous chloride containing small amounts of ferric hydroxide and ferric iron. Subsequently, by increasing the temperature, the remaining ferric hydroxide decomposes into high-melting-boiling-point metal oxides. On this basis, an iron reducing agent is mixed in to completely reduce the remaining ferric ions to ferrous ions, effectively preventing ferric ions from entering the finished product due to residual ferrous chloride tetrahydrate decomposition and ferrous chloride oxidation, thus ensuring the high purity of the product. Finally, utilizing the readily sublimable nature of ferrous chloride, high-purity anhydrous ferrous chloride is successfully obtained through a high-temperature distillation process. This process is simple and efficient, producing anhydrous ferrous chloride with extremely high purity. Compared with traditional methods for synthesizing ferrous chloride, this invention significantly reduces the content of impurities such as hydroxyl and ferric ions, greatly improving the chemical stability and electrochemical performance of ferrous chloride.

[0020] Preferably, in step S1, the iron-containing waste hydrochloric acid comes from the metallurgical and metal processing industry and is used to remove oxides and rust from the surface of steel. The reducing agent can be iron filings, iron sheets, iron mesh, or iron rings. On the one hand, this realizes the resource utilization of industrial waste, reduces the cost of raw material procurement, and meets environmental protection requirements. On the other hand, it clarifies that the reducing agent can be readily available materials such as iron filings and iron sheets, further reducing production costs, while ensuring the reduction effect of ferric ions and ensuring the economy and effectiveness of impurity control in the raw material stage.

[0021] Preferably, in step S2, the iron-containing waste hydrochloric acid is filtered through a filter press with an 800-1300 mesh filter cloth. The filter press is equipped with an 800-1300 mesh filter cloth. Filter cloths in this mesh range can effectively trap small insoluble impurities (such as fine silt, incompletely reacted micro solid particles, etc.) in the reduced solution. Compared with low-mesh filter cloths, this significantly improves the filtration accuracy, resulting in a clearer filtrate. This avoids micro impurities from being mixed into the subsequent crystallization process, laying the foundation for the subsequent preparation of high-purity crystals.

[0022] Preferably, in step S3, during the evaporation process, the specific gravity and solid-liquid ratio of the liquid material need to be continuously monitored. When they reach the preset standard, the feeding operation into the crystallization vessel is started immediately. Then, the crystallized liquid material formed in the crystallization vessel is transferred to a centrifuge, and ferrous chloride tetrahydrate crystals are extracted by high-speed centrifugation.

[0023] Preferably, in step S3, when the solid-liquid ratio of the concentrated crystallization reaches 5% to 40%, the crystallization vessel is discharged. Limiting the solid-liquid ratio of the concentrated crystallization to 5% to 40% allows for precise control of the concentration level: too low a ratio results in low crystal yield and low production efficiency; too high a ratio results in high viscosity, easily leading to excessive mother liquor impurities being trapped in the crystals, and increasing the difficulty of centrifugal separation. This limitation ensures crystal yield while reducing impurity trapping during crystallization, thus improving the initial purity of ferrous chloride tetrahydrate crystals.

[0024] A preferred solid-liquid ratio of 15%–30% is more suitable than 5%–40%, which promotes crystal growth, reduces impurities, and increases crystal purity. This range represents the optimal balance between crystal yield and purity. At this ratio, the crystallization rate of the feed solution is moderate, crystal growth is uniform, impurity encapsulation is minimized, and crystal separation from the mother liquor is more thorough during centrifugation, further improving the purity and yield of ferrous chloride tetrahydrate crystals and optimizing the balance between production efficiency and product quality.

[0025] Preferably, in step S4, the two-stage gentle heating process is as follows:

[0026] First, adjust the furnace temperature to the dehydration temperature and maintain it at this temperature to dehydrate the crystals. Throughout the dehydration process, monitor the discharge of water vapor in the furnace in real time. When the discharge of water vapor gradually decreases until it disappears completely and the furnace environment becomes stable, this indicates that the dehydration process has been completely completed.

[0027] Subsequently, following the preset heating program, the furnace temperature is gradually increased to carry out high-temperature calcination, which promotes the complete decomposition of the residual hydroxides at high temperature and transforms them into metal oxides with high melting points.

[0028] The two-stage gentle heating process, serving as a crucial link between "concentration and crystallization" and "mixing and ball milling," aims to maximize product yield and quality. By gently heating at a lower temperature, the crystal water is thoroughly removed, preventing residual moisture from entering the high-temperature section and hydrolyzing with ferrous chloride, thus preventing the formation of ferric hydroxide. This two-stage gentle heating process, through its step-by-step design of "vacuum low-temperature dehydration - high-temperature directional removal of hydroxides," not only solves the technical pain points of traditional calcination but also achieves a synergistic improvement in efficiency, safety, and product quality. This is one of the core innovations of this invention in the preparation of high-purity ferrous chloride.

[0029] Preferably, in step S4, the vacuum tube furnace is in a vacuum state of -0.1 MPa, the dehydration temperature is 120℃~160℃, the holding time is 8 hours or more, and the high-temperature calcination temperature is 400℃~700℃, more preferably 450℃~500℃. The -0.1 MPa high vacuum environment lowers the boiling point of water and accelerates the removal of water vapor. Combined with the low-temperature dehydration of 120℃~160℃ and the holding time of 8 hours or more, thorough dehydration can be achieved, while avoiding crystal oxidation or decomposition. The high-temperature calcination of 400℃~700℃ ensures that the residual hydroxides are fully decomposed into high-melting-point metal oxides, providing a guarantee for the subsequent separation and removal of hydroxyl impurities. At the same time, it avoids excessively high temperatures that could cause hydrolysis of ferrous chloride, preventing the formation of ferric hydroxide.

[0030] Preferably, the iron reducing agent in step S5 is high-purity iron powder or an iron-containing compound with reducing properties. When high-purity iron powder is mixed and ground with the calcined material, it will not introduce additional non-metallic or metallic impurities into the system, thus avoiding the problem of "adding other impurities in order to remove ferric iron" from the source of the reducing agent.

[0031] Both high-purity iron powder and iron-containing compounds such as ferrous oxide can be processed into fine particles (initial particle size is usually 10~50μm), similar in physical morphology to the calcined material (particle size is usually 50~100μm). Under the grinding action of a planetary ball mill, both can be simultaneously refined to the target particle size of 1~20μm, and during the grinding process, "stratification caused by density differences" (such as high-density metal reducing agent settling at the bottom and low-density non-metal reducing agent floating on the surface) is less likely to occur, ensuring uniform mixing.

[0032] Preferably, the ball mill used in step S6 is a planetary ball mill with a rotation speed of 400~650 r / min and a sintering temperature of 500℃~700℃. The ball mill, through intense impact, shearing, and grinding of the material, can refine the mixed particles of the calcined material and the iron reducing agent to 1~20 μm, achieving uniform dispersion at the molecular level. Scanning electron microscopy (SEM) observation reveals that the material particles exhibit a uniform, near-spherical distribution, without reducing agent agglomeration or material segregation, thus eliminating "reduction dead zones" and providing a structural basis for sufficient contact between ferric ions and the reducing agent. The temperature range of 500℃~700℃ precisely matches the reactivity window between the iron reducing agent (high-purity iron powder or reducing iron-containing compounds) and ferric ions.

[0033] Preferably, the vacuum distillation temperature in step S7 is 700℃~900℃, more preferably 750℃~800℃. A temperature of 700℃~900℃ allows ferrous chloride to fully sublimate while impurities such as high-melting-point metal oxides do not sublimate, thus achieving separation of the target product from impurities. The preferred temperature range of 750℃~800℃ ensures efficient sublimation of ferrous chloride while avoiding excessively high temperatures that would increase energy consumption and equipment burden, achieving a balance between efficient separation and economy, ultimately yielding high-purity anhydrous ferrous chloride.

[0034] The advantages of this invention are as follows: First, by employing a gentle calcination method, the hydroxides remaining during the dehydration process are converted into high-melting-point oxides, completely removing ferric hydroxide and creating extremely favorable conditions for subsequent distillation and purification processes. Second, given that ferrous chloride is easily oxidized to ferric chloride, this invention uses a mixed solid-phase sintering method, adding an iron reducing agent to reduce ferric ions to ferrous ions, thereby obtaining purer anhydrous ferrous chloride.

[0035] Compared with the prior art, the advantages of the present invention are as follows:

[0036] (1) The production method of high-purity anhydrous ferrous chloride of the present invention is simple in principle, the raw materials are readily available, the cost is low, and it is easy to mass-produce.

[0037] (2) The present invention adopts a mild heating process, which cleverly converts the residual hydroxide into high melting point oxide in the dehydration process, thereby achieving complete removal of ferric hydroxide and improving the purity of ferrous chloride.

[0038] (3) Given that ferrous chloride is easily oxidized to ferric chloride, this invention employs a mixed solid-phase sintering process to precisely add an iron reducing agent, thereby fully reducing ferric ions to ferrous ions. Based on this, high-purity anhydrous ferrous chloride is finally obtained through a fine treatment of high-temperature distillation.

[0039] (4) Compared with the traditional method of synthesizing ferrous chloride, the present invention significantly reduces the content of impurities such as hydroxyl groups and ferric ions, and greatly improves the chemical stability and electrochemical performance of ferrous chloride. Attached Figure Description

[0040] Figure 1 This is a process flow diagram of the present invention;

[0041] Figure 2 This is a crystal structure characterization diagram of the ferrous chloride product of the present invention. Detailed Implementation

[0042] The preparation and characterization of the present invention will be further described below:

[0043] Example 1:

[0044] (1) Synthesis of ferrous chloride tetrahydrate: Iron-containing waste hydrochloric acid was transported to a stirring tank, and excess iron filings were added. After stirring for 30 minutes, the mixture was filtered through a 200 μm pore size filter, and the filtrate was then transported to an evaporation system. When the specific gravity of the evaporated liquid reached 1.50, the liquid was discharged into a crystallization reactor, and cooling water was introduced into the jacket of the crystallization reactor. When the temperature of the liquid in the crystallization reactor dropped to 37°C, the liquid was discharged into a centrifuge, and finally ferrous chloride tetrahydrate was obtained.

[0045] (2) Dehydration of ferrous chloride tetrahydrate: The obtained 2 kg of ferrous chloride tetrahydrate was transferred to a vacuum tube furnace and connected with a circulating water vacuum pump to maintain a vacuum of -0.1 MPa. Then the temperature was gradually increased to 140°C and kept at that temperature for 8 hours until the water of crystallization was completely removed.

[0046] (3) Removal of ferric hydroxide: Following the preset heating program, the furnace temperature was gradually increased to 450℃ and held for 4 hours. The product obtained in step (2) was further processed to promote the complete decomposition of the residual hydroxide at high temperature, transforming it into an oxide with a high melting point. Testing revealed that the obtained product contained 97.5% ferrous chloride and Fe... 3+ The content is 0.5%, Mn content is 0.03%, Ni content is 0.01%, Cr content is 0.005%, and Zn content is 0.003%.

[0047] (4) High-energy ball milling: The ferrous chloride obtained in step (3) was accurately weighed, and 1% of its weight of high-purity iron powder was placed together in a planetary ball mill. The milling was continued for 4 hours at a speed of 600 r / min. Testing showed that the ferrous chloride content in the obtained product was as high as 97.995%, and the Fe content was... 3+ The content of [unspecified substance] is only 0.005%, Mn is 0.03%, Ni is 0.01%, Cr is 0.005%, and Zn is 0.003%.

[0048] (5) High-temperature purification: The product obtained in step (4) is packed into a quartz tube and then smoothly transferred to a high-vacuum distillation system. In this system, the absolute vacuum is precisely controlled to 0.001 Pa, and the temperature is set to 700℃ and maintained for 8 hours until ferrous chloride is completely sublimated and condensed. Testing showed that the ferrous chloride content in the obtained product was as high as 99.99%, and Fe... 3+ The content of [unspecified substance] is only 0.005%, Mn is 0.0015%, Ni is 0.0015%, Cr is 0.001%, and Zn is 0.0005%.

[0049] (6) Collection: Transfer the distilled ferrous chloride to a glove box for crushing and sieving.

[0050] Example 2: A method for synthesizing high-purity ferrous chloride, the process flow is as follows. Figure 1 ,

[0051] (1) Synthesis of ferrous chloride tetrahydrate: Iron-containing waste hydrochloric acid was transported to a stirring tank, and excess iron filings were added. After stirring for 30 minutes, the mixture was filtered through a 200 μm pore size filter, and the filtrate was then transported to an evaporation system. When the specific gravity of the evaporated liquid reached 1.50, the liquid was discharged into a crystallization reactor, and cooling water was introduced into the jacket of the crystallization reactor. When the temperature of the liquid in the crystallization reactor dropped to 37°C, the liquid was discharged into a centrifuge, and finally ferrous chloride tetrahydrate was obtained.

[0052] (2) Dehydration of ferrous chloride tetrahydrate: The obtained 2 kg of ferrous chloride tetrahydrate was transferred to a vacuum tube furnace and connected with a circulating water vacuum pump to maintain a vacuum of -0.1 MPa. Then the temperature was gradually increased to 140°C and kept at that temperature for 8 hours until the water of crystallization was completely removed.

[0053] (3) Removal of ferric hydroxide: Following the preset heating program, the furnace temperature was gradually increased to 450℃ and held for 4 hours. The product obtained in step (2) was further processed to promote the complete decomposition of the residual hydroxide at high temperature, transforming it into an oxide with a high melting point. Testing revealed that the obtained product contained 97.5% ferrous chloride and Fe... 3+ The content is 0.5%, Mn content is 0.03%, Ni content is 0.01%, Cr content is 0.005%, and Zn content is 0.003%.

[0054] (4) Mixing and Sintering: The obtained ferrous chloride was accurately weighed, and 1% of its weight of high-purity iron powder was placed together in a planetary ball mill. The mixture was continuously ball-milled at 500 r / min for 1 hour. Then, the finely ground mixture was evenly packed into a pre-cleaned and dried quartz tube, ensuring that the material was tightly packed and evenly distributed. Subsequently, the quartz tube was placed in a dedicated high-temperature sintering furnace, and the material was kept at 450℃ for 2 hours. Testing showed that the ferrous chloride content in the obtained product was as high as 97.999%, and the Fe content was... 3+ The content of [unspecified substance] is only 0.001%, Mn is 0.03%, Ni is 0.01%, Cr is 0.005%, and Zn is 0.003%.

[0055] (5) High-temperature purification: The product obtained in step (4) is packed into a quartz tube and then smoothly transferred to a high-vacuum distillation system. In this system, the absolute vacuum is precisely controlled to 0.001 Pa, and the temperature is set to 700℃ and maintained for 8 hours until ferrous chloride is completely sublimated and condensed. Testing showed that the ferrous chloride content in the obtained product was as high as 99.99%, and Fe... 3+The content of Cr is only 0.001%, Mn is 0.0015%, Ni is 0.0015%, Cr is 0.001%, and Zn is 0.0005%;

[0056] (6) Collection: Transfer the distilled ferrous chloride to a glove box for crushing and sieving. See the crystal structure characterization diagram of the ferrous chloride product. Figure 2 .

[0057] Comparative analysis of Example 1 and Example 2:

[0058] Example 1 demonstrates that high-energy ball milling alone can promote the reaction between the material and the iron reducing agent, eliminating the need for high-temperature calcination, but the processing time is long. Example 2 reduces the high-energy ball milling speed and processing time, but requires high-temperature calcination to ensure a complete reaction between the material and the iron reducing agent, and the reaction is more thorough than in Example 1, therefore Fe... 3+ The content is even lower.

[0059] Example 3:

[0060] (1) Synthesis of ferrous chloride tetrahydrate: Iron-containing waste hydrochloric acid was transported to a stirring tank, and excess iron filings were added. After stirring for 30 minutes, the mixture was filtered through a 200 μm pore size filter, and the filtrate was then transported to an evaporation system. When the specific gravity of the evaporated liquid reached 1.50, the liquid was discharged into a crystallization reactor, and cooling water was introduced into the jacket of the crystallization reactor. When the temperature of the liquid in the crystallization reactor dropped to 37°C, the liquid was discharged into a centrifuge, and finally ferrous chloride tetrahydrate was obtained.

[0061] (2) Dehydration of ferrous chloride tetrahydrate: The obtained 2 kg of ferrous chloride tetrahydrate was transferred to a vacuum tube furnace and connected with a circulating water vacuum pump to maintain a vacuum of -0.1 MPa. Then the temperature was gradually increased to 140°C and kept at that temperature for 8 hours until the water of crystallization was completely removed.

[0062] (3) Removal of ferric hydroxide: Following the preset heating program, the furnace temperature was gradually increased to 450℃ and held for 4 hours. The product obtained in step (2) was further processed to promote the complete decomposition of the residual hydroxide at high temperature, transforming it into an oxide with a high melting point. Testing revealed that the obtained product contained 97.5% ferrous chloride and Fe... 3+ The content is 0.5%, Mn content is 0.03%, Ni content is 0.01%, Cr content is 0.005%, and Zn content is 0.003%.

[0063] (4) Mixing and Sintering: The obtained ferrous chloride was accurately weighed, and 1% of its weight of high-purity iron powder was placed together in a planetary ball mill. The mixture was continuously ball-milled at 500 r / min for 1 hour. Then, the finely ground mixture was evenly packed into a pre-cleaned and dried quartz tube, ensuring that the material was tightly packed and evenly distributed. Subsequently, the quartz tube was placed in a dedicated high-temperature sintering furnace, and the material was kept at 450℃ for 2 hours. Testing showed that the ferrous chloride content in the obtained product was as high as 97.999%, and the Fe content was... 3+ The content of [unspecified substance] is only 0.001%, Mn is 0.03%, Ni is 0.01%, Cr is 0.005%, and Zn is 0.003%.

[0064] (5) High-temperature purification: The product obtained in step (4) is packed into a quartz tube and then smoothly transferred to a high-vacuum distillation system. In this system, the absolute vacuum is precisely controlled to 0.01 Pa, and the temperature is set to 800℃ and maintained for 8 hours until ferrous chloride is completely sublimated and condensed. Testing showed that the ferrous chloride content in the obtained product was as high as 99.99%, and Fe... 3+ The content of [unspecified substance] is only 0.001%, Mn is 0.0015%, Ni is 0.0015%, Cr is 0.001%, and Zn is 0.0005%.

[0065] (6) Collection: Transfer the distilled ferrous chloride to a glove box for crushing and sieving.

[0066] Comparative analysis of Examples 2 and 3:

[0067] Compared to Example 2, Example 3 achieved an absolute vacuum level one order of magnitude higher, at 0.01 Pa; Example 2 achieved 0.001 Pa. Specifically, Example 3 demonstrates that high-vacuum distillation cannot be achieved with only 0.001 Pa; lowering the vacuum level by one order of magnitude and increasing the sintering temperature can also achieve the desired effect.

[0068] Comparative Example 1:

[0069] The specific method is the same as in Example 2, except that step (4) is removed and mixing and sintering are not performed. The remaining steps are the same as in Example 2.

[0070] Testing revealed that the product contained 97% ferrous chloride and Fe. 3+ The content of Cr is 0.5%, Mn is 0.0015%, Ni is 0.0015%, Cr is 0.001%, and Zn is 0.0005%.

[0071] Comparative analysis was conducted: The analysis concluded that the main reason was the lack of analysis of Fe. 3+They are processed separately. During the subsequent high-temperature distillation process, ferric chloride and ferrous chloride sublimate together and enter the product, resulting in a significant decrease in product purity.

[0072] Comparative Example 2:

[0073] The specific method is the same as in Example 2. The specific difference is that the calcination mechanism in step (3) of removing hydroxyl iron oxide is changed from 450°C for 4 hours to 300°C for 4 hours. The remaining steps are the same as in Example 2.

[0074] Testing revealed that the product contained 98.9% ferrous chloride, 1% ferric hydroxide, and Fe... 3+ The content of Cr is 0.005%, Mn is 0.0015%, Ni is 0.0015%, Cr is 0.001%, and Zn is 0.0005%.

[0075] Comparative analysis revealed that the main reason was the low calcination temperature during the removal of hydroxyl iron oxide, which prevented the complete conversion of hydroxyl iron oxide into metal oxides, resulting in impurities in the final product.

[0076] As can be seen from the above examples, the purification process of this invention can effectively remove ferric hydroxide and Fe. 3 + The resulting ferrous chloride product has high purity, which fully guarantees its chemical stability and electrochemical performance.

[0077] The above provides a detailed description of a method for synthesizing high-purity ferrous chloride provided by the present invention. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Modifications and improvements to the present invention are possible without exceeding the concept and scope specified in the appended claims. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for synthesizing high-purity ferrous chloride, characterized in that, The steps are as follows: S1. Add iron powder to iron-containing hydrochloric acid in a certain proportion for reduction treatment to reduce all ferric ions to ferrous ions; S2. The iron-containing hydrochloric acid that has undergone reduction treatment is then filtered under pressure to completely remove any remaining insoluble impurities from the solution; S3. The clarified filtrate obtained after fine filtration is sent to the evaporation system for efficient concentration to extract ferrous chloride tetrahydrate crystals; S4. Place the ferrous chloride tetrahydrate crystals into a vacuum tube furnace, and evacuate the furnace environment to a high vacuum state to ensure that the dehydration process is carried out in a low oxygen and low impurity environment. Perform a two-stage mild heating process to promote the complete decomposition of the residual hydroxide at high temperature and transform it into a metal oxide with a high melting point. S5. Weigh the material obtained after step S4 and add iron reducing agent. Transfer the mixture to a ball mill under an argon atmosphere for uniform mixing and fine ball milling. S6. The mixture after fine grinding in a ball mill is loaded into a quartz tube and placed in a special high-temperature sintering furnace to allow the material to react fully in a high-temperature environment, reducing the residual ferric ions to ferrous ions. S7. After sintering, the quartz tube is transferred to a high-vacuum distillation system. By controlling the distillation temperature and pressure, and utilizing the sublimation properties of ferrous chloride, it is efficiently separated from the mixture and collected by condensation, ultimately obtaining a high-purity, high-crystallinity anhydrous ferrous chloride product.

2. The method for synthesizing high-purity ferrous chloride according to claim 1, characterized in that: In step S1, the iron-containing waste hydrochloric acid comes from the metallurgical and metal processing industry and is used to remove oxides and rust from the surface of steel. The reducing agent can be iron filings, iron sheets, iron mesh, or iron rings.

3. The method for synthesizing high-purity ferrous chloride according to claim 1, characterized in that: In step S2, the iron-containing waste hydrochloric acid is filtered through a filter press with 800-1300 mesh filter cloth.

4. The method for synthesizing high-purity ferrous chloride according to claim 1, characterized in that: In step S3, during the evaporation process, the specific gravity and solid-liquid ratio of the liquid material need to be continuously monitored. When they reach the preset standard, the feeding operation into the crystallization vessel is started immediately. Then, the crystallized liquid material formed in the crystallization vessel is transferred to a centrifuge, and ferrous chloride tetrahydrate crystals are extracted by high-speed centrifugation.

5. The method for synthesizing high-purity ferrous chloride according to claim 1, characterized in that: In step S3, when the solid-liquid ratio of the crystallized concentrate reaches 5% to 40%, the crystallization vessel is discharged, preferably with a solid-liquid ratio of 15% to 30%.

6. The method for synthesizing high-purity ferrous chloride according to claim 1, characterized in that: In step S4, the two-stage gentle heating process is as follows: First, adjust the furnace temperature to the dehydration temperature and maintain it at this temperature to dehydrate the crystals. Throughout the dehydration process, monitor the discharge of water vapor in the furnace in real time. When the discharge of water vapor gradually decreases until it disappears completely and the furnace environment becomes stable, this indicates that the dehydration process has been completely completed. Subsequently, following the preset heating program, the furnace temperature is gradually increased to carry out high-temperature calcination, which promotes the complete decomposition of the residual hydroxides at high temperature and transforms them into metal oxides with high melting points.

7. The method for synthesizing high-purity ferrous chloride according to claim 6, characterized in that: In step S4, the vacuum tube furnace is in a vacuum state of -0.1 MPa, the dehydration temperature is 120℃~160℃, the holding time is 8 hours or more, and the high-temperature calcination temperature is 400℃~700℃, more preferably 450℃~500℃.

8. The method for synthesizing high-purity ferrous chloride according to claim 1, characterized in that: In step S5, the iron reducing agent is high-purity iron powder or an iron-containing compound with reducing properties.

9. The method for synthesizing high-purity ferrous chloride according to claim 1, characterized in that: In step S6, the ball mill is a planetary ball mill with a rotation speed of 400 r / min to 650 r / min and a sintering temperature of 500℃ to 700℃.

10. The method for synthesizing high-purity ferrous chloride according to claim 1, characterized in that: In step S7, the vacuum distillation temperature is 700℃~900℃, more preferably 750℃~800℃.

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