Electrodialysis device and method for selectively synthesizing cobalt ferricyanate and efficiently extracting potassium and application

Abstract

The invention relates to an electrodialysis device and method for selectively synthesizing cobalt ferricyanate and efficiently extracting potassium and application. A membrane stack structure of the electrodialysis device sequentially comprises a first anion exchange membrane, a cation exchange membrane, a monovalent and divalent cation selective separation membrane and a second anion exchange membrane to form an anode chamber, a first raw material chamber, a product chamber, a second raw material chamber and a cathode chamber. Under the driving of a direct-current electric field, Co < 2 + > and [Fe (CN) 6] < 4-> are directionally migrated to a product chamber for reaction, and a CoHCF material with smooth surface, uniform size and high crystallinity is generated. The method effectively inhibits side reactions, and improves the purity and structural controllability of the material. The separation coefficient of the prepared CoHCF on K < + > in a high-sodium solution with the ratio of K < + > to Na < + > being 1: 30 reaches up to 13.05, and the CoHCF is suitable for efficient selective extraction of potassium resources in seawater and brine.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of wastewater treatment and functional material synthesis, and particularly relates to an electrodialysis device, method and application for selectively synthesizing cobalt hexacyanoferrate and efficiently extracting potassium. BACKGROUND

[0002] With the continuous growth of global demand for high-purity potassium compounds, especially in the fields of food security and high-end chemical production (such as electronic-grade potassium hydroxide), efficient separation of potassium ions (K + ) and sodium ions (Na + ) from complex systems has become an urgent scientific and technological challenge. The target resources include concentrated brine from seawater desalination and salt lake brine, which are characterized by extremely low potassium-to-sodium ratios (K + / Na + ≈1:20 or even lower). However, K + and Na + have highly similar physicochemical properties, such as the same charge and similar hydrated ion radii, which severely restricts the economic feasibility and separation selectivity of traditional separation methods (such as fractional crystallization, adsorption, and co-precipitation) in high-sodium backgrounds.

[0003] Among existing separation technologies, membrane-based processes, such as electrodialysis (ED), show good application prospects due to their low energy consumption and potential for continuous operation. The performance of electrodialysis is critically dependent on ion exchange membranes, especially cation exchange membranes (CEMs) with high selectivity for target ions. However, current electrodialysis systems are still limited by the availability of high-performance monovalent selective CEMs. Although surface-modified CEMs (such as PEI / PSS coatings or nanocomposites) have been extensively studied to enhance their selectivity for monovalent ions, these modified membranes generally suffer from insufficient stability, complex preparation processes, and easy deactivation of active centers in high-salinity, strong-ion-competition environments, greatly limiting their large-scale application in extremely high-sodium-to-potassium-ratio actual brine systems.

[0004] On the other hand, cobalt hexacyanoferrate (CoHCF), as a representative of Prussian blue analogues (PBAs), exhibits significant advantages in ion recognition and selective separation due to its open framework structure, tunable pore size, and abundant cyanide coordination sites. The highly ordered lattice channels of PBAs allow precise regulation of ion selectivity by changing the central metal ion and its valence state, especially exhibiting high affinity for K + , which is mainly attributed to the strong electrostatic interaction between K +The size matching with the lattice hole and the strong ion-skeleton interaction. The mixed valence characteristic (involving cobalt and ferricyanide center) of CoHCF can also adjust its electronic structure through redox reaction, thereby further enhancing the adsorption capacity of specific ions. However, the traditional CoHCF synthesis method (such as coprecipitation) is difficult to effectively control the crystal morphology, pore size distribution and purity of the material, and is prone to cause competitive side reactions (such as the generation of Fe(OH)3), resulting in the unsatisfactory selective adsorption capacity and long-term cycle stability of the final material.

[0005] More importantly, the conventional electrodialysis device mainly focuses on desalination or solution concentration, and the homogeneous and repeated membrane stack structure cannot realize the spatial confinement and precise delivery of reaction ions, and thus is not suitable for the controllable and efficient synthesis of high-value functional materials such as CoHCF. The prior art lacks a specialized device and process that can combine the directional mass transfer advantage of electrodialysis with the in-situ synthesis requirement of functional materials.

[0006] Therefore, in view of the above technical bottlenecks, it is urgent to develop an electrodialysis device and supporting process specially used for synthesizing CoHCF and other Prussian blue analogues, so as to realize the efficient and controllable synthesis of materials and ultimately apply them to the high-selectivity extraction of potassium resources under high-sodium background. SUMMARY

[0007] The present application relates to an electrodialysis device, method and application for selectively synthesizing cobalt hexacyanoferrate and efficiently extracting potassium. The method effectively suppresses side reactions and realizes precise control of material morphology and composition. The synthesized CoHCF material exhibits excellent selective adsorption performance for K + under high-sodium background (K + / Na + =1:30), with a separation coefficient as high as 13.05, providing a new technical and material solution for efficient extraction of potassium resources from seawater or salt lake brine.

[0008] In one aspect, the present application provides an electrodialysis device for selectively synthesizing cobalt hexacyanoferrate and efficiently extracting potassium. The device comprises at least one synthesis unit, each synthesis unit comprising, in sequence along the solution flow direction, a first anion exchange membrane (2), a cation exchange membrane (3), a divalent cation selective separation membrane (4), and a second anion exchange membrane (5), thereby forming and isolating five independent chambers: an anode chamber (7) surrounded by the end plate (1) and the first anion exchange membrane; a first raw material chamber (8) surrounded by the first anion exchange membrane and the cation exchange membrane; a product chamber (9) surrounded by the cation exchange membrane and the divalent cation selective separation membrane; The second raw material chamber (10) is surrounded by a divalent cation selective separation membrane and a second anion exchange membrane; The cathode chamber (11) is surrounded by the second anion exchange membrane and the second end plate; The anode chamber and the cathode chamber are provided with electrodes and connected to a direct current power supply; the first raw material chamber is used for introducing and circulating cobalt salt solution, the second raw material chamber is used for introducing and circulating ferrocyanide salt solution, and the product chamber is used for receiving Co 2+ and [Fe(CN)6] 4- and generating cobalt hexacyanoferrate precipitate.

[0009] Preferably, the anode chamber (7), the first raw material chamber (8), the product chamber (9), the second raw material chamber (10) and the cathode chamber (11) are respectively connected to the respective solution storage tanks through independent circulating pumps, forming five independent closed-loop circulating systems.

[0010] On the other hand, the application also provides a use method of the electrodialysis device for selectively synthesizing cobalt hexacyanoferrate and efficiently extracting potassium, comprising the following steps: (1) Device assembly and solution filling: filling electrode solution into the anode chamber and the cathode chamber; filling cobalt salt solution into the first raw material chamber; filling ferrocyanide salt solution into the second raw material chamber; filling deionized water or dilute electrolyte solution as initial reaction medium into the product chamber; (2) Electric field driven synthesis: starting the direct current power supply, operating in constant current mode, controlling the current to be between 0.1A and 0.15A, and making Co 2+ and [Fe(CN)6] 4- directionally migrate to the product chamber for co-precipitation reaction, the reaction temperature is 27-30℃, and the reaction time is 4-12 hours; (3) Post-treatment: after the reaction is completed, collecting the precipitate in the product chamber, and filtering, washing and drying to obtain cobalt hexacyanoferrate (CoHCF) active material.

[0011] Preferably, the current in the constant current mode is preferably 0.15A.

[0012] Preferably, the reaction time is preferably 8 hours.

[0013] Preferably, the cobalt salt solution is CoCl2 solution with a concentration of 0.1M; the ferrocyanide salt solution is Na4[Fe(CN)6] solution with a concentration of 0.05M; and the electrode solution is 0.1M NaCl solution.

[0014] Preferably, the drying is vacuum drying at 80℃ for 12 hours.

[0015] Preferably, the Co / Fe molar ratio of the material is close to 2:1.

[0016] The application also provides an application of the cobalt hexacyanoferrate active material in selectively adsorbing potassium ions from a mixed solution containing potassium and sodium ions.

[0017] Preferably, the molar ratio of K + to Na + in the mixed solution ranges from 1:1 to 1:30, and the separation coefficient of the CoHCF active material to K + is up to 13.05.

[0018] In summary, the application has the following beneficial effects: The core beneficial effect of the application lies in the synergistic innovation of the device and the process. By designing the special membrane stack structure of “negative-positive-one-two-valent positive-negative”, a reaction chamber with physical isolation but electric field linkage is constructed, and for the first time, the electrodialysis technology is successfully applied to the controllable synthesis of functional materials. The device realizes the directional transmission and spatial confinement of the reaction ions (Co 2+ and [Fe(CN)6] 4- ) to the product chamber, fundamentally solving the key problems such as uneven initial concentration of reactants, multiple by-products, and uncontrollable morphology in the traditional coprecipitation method. By accurately controlling the electric field parameters, the occurrence of competitive side reactions such as Fe(OH)3 is effectively inhibited, providing a reliable platform for the in-situ synthesis of high-quality and high-purity CoHCF crystals.

[0019] Based on the above-mentioned innovative process, the CoHCF material synthesized exhibits excellent microstructure and ion selectivity performance. The material has a smooth surface and uniform size, and under an extremely high-sodium background (K + / Na + ≈1:30), the separation coefficient to K + is up to 13.05, showing excellent selective adsorption capacity. At the same time, the preparation process provided by the application is simple, low in cost and easy to scale up, opening up a new and scalable technical path for large-scale production of high-efficiency adsorption materials for seawater potassium resource recovery. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a diagram of the membrane stack; Figure 2 is a diagram of the internal structure of the membrane stack; Figure 3 is a scanning electron microscope (SEM) image of the CoHCF-8h material prepared in Example 2; Figure 4 is an SEM corresponding EDS diagram of the electrodialysis reaction time of 4h, 8h, 12h. DETAILED DESCRIPTION

[0021] The application will be further described in detail below in conjunction with the examples.

[0022] Embodiment Embodiment 1 As Figure 1 shown, the application provides a special electrodialysis device for synthesizing cobalt hexacyanoferrate active material, which comprises at least one synthesis unit, each synthesis unit is sequentially composed of a first anion exchange membrane (2), a cation exchange membrane (3), a divalent cation selective separation membrane (4) and a second anion exchange membrane (5) along the solution flow direction, thereby forming and isolating five independent chambers: an anode chamber (7) surrounded by the end plate (1) and the first anion exchange membrane; a first raw material chamber (8) surrounded by the first anion exchange membrane and the cation exchange membrane; a product chamber (9) surrounded by the cation exchange membrane and the divalent cation selective separation membrane; a second raw material chamber (10) surrounded by the divalent cation selective separation membrane and the second anion exchange membrane; a cathode chamber (11) surrounded by the second anion exchange membrane and the second end plate; Among them, the anode chamber and the cathode chamber are provided with electrodes and connected to a direct current power supply; the first raw material chamber is used for introducing and circulating cobalt salt solution, the second raw material chamber is used for introducing and circulating ferrocyanide salt solution, the product chamber is used for receiving Co 2+ and [Fe(CN)6] 4- and generating cobalt hexacyanoferrate precipitate.

[0023] The anode chamber (7), the first raw material chamber (8), the product chamber (9), the second raw material chamber (10) and the cathode chamber (11) are respectively connected to the solution storage tank through independent circulating pumps, forming five independent closed loop circulation systems.

[0024] Embodiment 2 A synthesis and adsorption test of CoHCF material, the specific steps are as follows: 1) Inject 400mL of 0.1M NaCl solution into the anode chamber and the cathode chamber; inject 400mL of 0.1M CoCl2·6H2O solution into the first raw material chamber; inject and circulate 400mL of deionized water as the initial reaction medium into the product chamber; inject 400mL of 0.05M Na4[Fe(CN)6] solution into the second raw material chamber. Under the action of a direct current field, control the current to be constant at 0.15A, the voltage range is 10-15V, the solution flow rate is 88mL / min, and the reaction is carried out at room temperature (27-30℃) for 8 hours, and the reaction principle is as Figure 2 shown.

[0025] 2) Material post-processing: After the reaction is completed, the CoHCF precipitate generated in the product chamber is back-flushed, and then filtered and washed with deionized water for 3 times, and then dried at 80°C under vacuum for 12 hours to obtain CoHCF-8h active material.

[0026] 3) Adsorption performance test: 0.1 g of the CoHCF-8h material prepared above is weighed and added to 100 mL of a mixed solution with a potassium-sodium molar ratio of 1:30. The mixture is placed in a constant temperature shaker, and adsorbed at 35°C under the condition of 150 rpm oscillation for 0.5 hours to reach equilibrium.

[0027] The obtained CoHCF-8h material has a K + / Na + selective adsorption performance, with a K + Separation coefficient as high as 13.05. As Figure 3 shown, the structure of the material presents a clear ridge line, smooth surface and uniform size under scanning electron microscopy (SEM).

[0028] Example 3 Synthesis and adsorption test of a CoHCF material, the specific steps are as follows: The difference between this example and Example 2 is that the same electro-dialysis device is used, and the reaction time of the electro-dialysis synthesis stage is controlled to be 4 hours, 8 hours and 12 hours respectively, in order to explore the influence of reaction time on the structure and performance of the material. The other experimental conditions and steps are exactly the same as those of Example 2.

[0029] As Figure 4 shown, the SEM and EDS images corresponding to the electro-dialysis reaction time of 4h, 8h and 12h, and the column chart in the figure is the weight percentage and atomic percentage.

[0030] The performance test results show that the selective coefficients of the CoHCF-4h, CoHCF-8h and CoHCF-12h materials obtained in Example 2 for K + are 11.37, 13.05 and 3.76 respectively. X-ray diffraction (XRD) analysis shows that the crystallinity is 6.53%, 23.43% and 13.74% respectively. In summary, the CoHCF-8h material synthesized by using the device for 8 hours has the best crystal structure integrity and ion selectivity.

[0031] Example 4 Adsorption test of a CoHCF material, the specific steps are as follows: The difference between the present embodiment and embodiment 2 is that CoHCF-8h material is used, the adsorption test environment is changed, and the adsorption test is carried out in a mixed solution with a potassium-sodium molar ratio of 1:1, and other experimental conditions and steps are the same as those in step 3) of embodiment 2.

[0032] The present embodiment is tested in an environment with a potassium-sodium molar ratio of 1:1, and the obtained CoHCF-4h, CoHCF-8h and CoHCF-12h materials have a selectivity coefficient of 0.21, 2.76 and 0.23, respectively, for K + . This result further confirms the universal selective advantage of the CoHCF-8h material synthesized by the device in different sodium ion backgrounds, especially in a high-sodium environment (K + / Na + =1:30) where the selectivity is most prominent.

[0033] Embodiment 5 The synthesis and adsorption test of a CoHCF material are as follows: The difference between the present embodiment and embodiment 1 is that the direct current is increased to 0.5 A, and other experimental conditions and steps are the same as those in embodiment 1.

[0034] The experimental results show that when the current is increased to 0.5 A, the voltage on both sides of the membrane stack is too high, resulting in the ionization of part of the [Fe(CN)6] 4- complex ions during migration, which cannot effectively combine with Co 2+ in the product chamber to generate the target CoHCF material. This comparison proves that it is crucial to control the synthesis current in the device of the present application within the range of 0.1 A-0.15 A (preferably 0.15 A) for the successful synthesis of high-purity, complete-crystal CoHCF material.

[0035] The above are preferred embodiments of the present application, and do not limit the protection scope of the present application, so: any equivalent changes made in the structure, shape, principle of the present application should be covered within the protection scope of the present application.

Claims

1. An electrodialysis device for selectively synthesizing cobalt hexacyanoferrate and efficiently extracting potassium, characterized in that, The device comprises at least one synthesis unit, which is sequentially provided with an end plate (1), a first anion exchange membrane (2), a cation exchange membrane (3), a divalent cation selective separation membrane (4), a second anion exchange membrane (5), and a second end plate (6) along the solution flow direction. The end plate (1) and the first anion exchange membrane (2) form an anode chamber (7). The first anion exchange membrane (2) and the cation exchange membrane (3) form a first raw material chamber (8). The cation exchange membrane (3) and the divalent cation selective separation membrane (4) form a product chamber (9). The divalent cation selective separation membrane (4) and the second anion exchange membrane (5) form a second raw material chamber (10). The second anion exchange membrane (5) and the second end plate (6) form a cathode chamber (11). The anode chamber (7) and the cathode chamber (11) are provided with electrodes and connected to a direct current power supply; the first raw material chamber (8) is used for feeding and circulating cobalt salt solution, the second raw material chamber (10) is used for feeding and circulating ferrocyanide solution, and the product chamber (9) is used for receiving Co 2+ and [Fe(CN)6] 4- and generates cobalt ferricyanide precipitate.

2. The electrodialysis unit for selective synthesis of cobalt hexacyanoferrate and efficient potassium extraction according to claim 1, characterized in that, The anode chamber (7), the first raw material chamber (8), the product chamber (9), the second raw material chamber (10), and the cathode chamber (11) are respectively connected to a solution storage tank through an independent circulating pump, forming five independent closed-loop circulation systems.

3. A method for using the electrodialysis device for selectively synthesizing cobalt hexacyanide and efficiently extracting potassium according to any one of claims 1 or 2, characterized in that, The method comprises the following steps: (1) Device assembly and solution filling: filling electrode solution into the anode chamber (7) and the cathode chamber (11); filling cobalt salt solution into the first raw material chamber (8); filling ferrocyanide solution into the second raw material chamber (10); and filling deionized water or dilute electrolyte solution as the initial reaction medium into the product chamber (9); (2) Electric field driven synthesis: start the direct current power supply, run in constant current mode, control the current between 0.1 A and 0.15 A, and make Co 2+ and [Fe(CN)6] 4- migrate to the product chamber for coprecipitation reaction, the reaction temperature is 27°C to 30°C, and the reaction time is 4 to 12 hours; (3) Post-treatment: after the reaction is completed, the precipitate in the product chamber is collected, filtered, washed, and dried to obtain the cobalt hexacyanoferrate active material.

4. A method of using the electrodialysis unit for selective synthesis of cobalt hexacyanoferrate and efficient potassium extraction as claimed in claim 3, wherein, In step (2), the constant current mode current is preferably 0.15 A.

5. The method of using the electrodialysis unit for selective synthesis of cobalt hexacyanoferrate and efficient potassium extraction as claimed in claim 3, wherein, In step (2), the reaction time is preferably 8 hours.

6. A method of using the electrodialysis unit for selective synthesis of cobalt hexacyanoferrate and efficient potassium extraction as claimed in claim 3, wherein, In step (1), the cobalt salt solution is a CoCl2 solution with a concentration of 0.1 M; the ferrocyanide solution is a Na4[Fe(CN)6] solution with a concentration of 0.05 M; and the electrode solution is a 0.1 M NaCl solution.

7. A method of using the electrodialysis unit for selective synthesis of cobalt hexacyanoferrate and efficient potassium extraction as claimed in claim 3, wherein, In step (3), the drying is vacuum drying at 80°C for 12 hours.

8. A cobalt hexacyanoferrate (CoHCF) active material prepared by the method of any one of claims 3 to 7, characterized in that, The Co / Fe molar ratio of the material is close to 2:

1.

9. Use of the cobalt hexacyanoferrate active material according to claim 8 for selectively adsorbing potassium ions from a mixed solution containing potassium and sodium ions.

10. Use according to claim 9, characterized in that, The molar ratio of K + to Na + ranges from 1:1 to 1:30.

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