A coupled ion-rectification displacement electrodialysis system and its application

Abstract

The application discloses a kind of coupled ion rectification displacement electrodialysis system and its application, it is the effective coupling of ion rectification technology and displacement electrodialysis technology, namely, in raw material room and byproduct room between stacking same kind ion membrane, construct ion rectification room, utilize the characteristics that cation exchange membrane mainly passes through cation, anion exchange membrane mainly passes through anion, realize multiple barrier to the same ion leakage, finally realize the promotion of product purity.The coupled system of the application can realize the production of high-purity lithium hydroxide and the like, especially the production of battery-grade lithium hydroxide, is expected to shorten the subsequent refining process route in the production process of lithium hydroxide, reduce the production cost of lithium hydroxide, improve the purity, quality and recovery rate of lithium hydroxide product.

Description

Technical Field

[0001] This invention belongs to the field of electrically driven membrane separation, specifically relating to a displacement electrodialysis system coupled with ion distillation and its application, particularly in the production of high-purity lithium hydroxide. Background Technology

[0002] High-quality lithium salts are indispensable raw materials for lithium-ion battery new energy vehicles. Among them, lithium hydroxide is one of the three core raw materials for battery lithium products, especially the high-nickel ternary cathode material widely used in high-performance power batteries (partial NCM622, all NCM811, 90505, and NCA). In recent years, driven by the lithium-ion battery industry, the demand for lithium hydroxide has continued to rise. According to statistics, the global demand for LiOH was approximately 200,000 tons in 2021, and it is estimated that the demand for LiOH will reach 540,000 tons in 2025, with a compound annual growth rate of 38.78%.

[0003] Currently, lithium is abundant in lake brines, lithium ores, and spent lithium-ion batteries. To utilize these lithium resources to produce LiOH, a causticization process is required. In traditional industry, this process often occurs under heterogeneous conditions, with the main product, lithium hydroxide, and byproducts often mixed in a homogeneous form. Separation, purification, and refining require separation methods involving phase transitions. For example, lithium hydroxide can be prepared by adding sodium hydroxide to lithium sulfate obtained from acid leaching of ore; or by producing crude lithium carbonate from salt lake brine and then adding refined lime slurry to the crude lithium carbonate for causticization; or by adding sodium hydroxide to a lithium-containing solution obtained from acid leaching of spent batteries for causticization. However, these preparation methods all face many common problems: (1) In the subsequent crystallization and separation process, the purity of LiOH products is low due to the presence of raw materials and by-products required in the "causticization" process; (2) Due to multiple crystallizations during the refining process, a large amount of lithium element is lost; (3) A large amount of waste salt is generated during the process, resulting in high process costs and serious environmental pollution; (4) Existing lithium hydroxide production routes mostly adopt the synergistic coupling between multiple technical units, resulting in long technical routes, complex processes, and low integration. Therefore, it is urgent to develop a simplified, efficient, and environmentally friendly LiOH production route to maximize resource utilization.

[0004] Displacement electrodialysis is a high-capacity, low-cost, easy-to-operate, and environmentally friendly platform technology that combines the effects of concentration, desalination, and metathesis reactions. It has been used to produce LiOH. Its principle is as follows: in a displacement electrodialysis membrane stack, anion and cation exchange membranes are arranged alternately to form a by-product chamber, a first feed chamber, a main product chamber, and a second feed chamber. Anions and cations in the two feed chambers move to the two product chambers respectively under the influence of an electric field, forming two new salts. Although displacement electrodialysis is a clean and sustainable technology, problems such as ion leakage and low product purity still exist, mainly due to the limited permeation selectivity of the ion exchange membranes.

[0005] Ion exchange membranes achieve selective passage of different ions based on the charge type of the functional groups within the membrane, utilizing the principle of like-charge repulsion. Taking anion exchange membranes as an example, the membrane contains many positively charged functional groups, allowing anions to pass through while blocking cations. The migration number of an ion exchange membrane refers to the ratio of the amount of charge transported by a specific ion to the total charge transported. It characterizes the membrane's selective permeability to oppositely charged ions and its repulsiveness to like-charged ions. For example, the migration number of the AMX anion exchange membrane is 99.9% (data from the Journal of Membrane Science 325 (2008) 215-222), indicating that anions transport 99.9% of the total charge transported, while cations transport only 0.1%. The migration number of an ion exchange membrane does not actually reach 100%, meaning that cation exchange membranes do not only allow cations to pass through, and anion exchange membranes do not only allow anions to pass through. A higher migration number indicates higher selective permeability to oppositely charged ions and higher repulsiveness to like-charged ions. The ion leakage problem in displacement electrodialysis stems from the fact that the migration number of the ion exchange membrane cannot reach 100%. Under the influence of the electric field, some cations in the by-product chamber will pass through the anion exchange membrane towards the cathode, enter the feed chamber, and then pass through the cation exchange membrane towards the cathode, eventually reaching the main product chamber. Similarly, some anions in the by-product chamber will pass through the cation exchange membrane towards the anode, enter the feed chamber, and then pass through the anion exchange membrane towards the anode, eventually reaching the main product chamber, thus contaminating the main product. Therefore, the production of LiOH or other products using displacement electrodialysis inevitably requires subsequent refining and purification steps.

[0006] Ion distillation is a novel electro-driven membrane separation technology. This technology arranges multiple identical ion exchange membranes according to the principle of "same type, same side," utilizing the multi-stage sieving mechanism of specific ions in the stacked ion exchange membranes and the amplification effect of ion selectivity to ultimately achieve precise separation of specific ions. To effectively address the problems of ion leakage and low product purity, this invention effectively couples ion distillation technology with displacement electrodialysis technology. Specifically, identical ion exchange membranes are stacked between the feed chamber and the by-product chamber to construct an ion distillation chamber. Utilizing the characteristic that cation exchange membranes primarily permeate cations and anion exchange membranes primarily permeate anions, this allows for multiple blocking of leaked ions of the same type (here, "same ion" refers to ions with the same charge type as the groups within the membrane; for example, if the groups within the anion exchange membrane are positively charged, then "same ion" refers to cations, and the anion exchange membrane can block leaked cations), ultimately improving product purity. In previous studies, ion distillation was used only as a standalone technology and was not coupled with traditional electrodialysis or other techniques. Therefore, this invention not only improves the economic and environmental benefits in the field of lithium hydroxide preparation, but also successfully couples ion distillation technology with other electrodialysis technologies, achieving a "1+1>2" effect. Summary of the Invention

[0007] To avoid the problem of low purity of target products generated by displacement electrodialysis for lithium hydroxide or other products, this invention provides a displacement electrodialysis system coupled with ion distillation. The system aims to effectively improve product purity by constructing an ion distillation chamber, based on the characteristics of displacement electrodialysis that can effectively separate main products and by-products, the multi-stage sieving mechanism of ions in the functional membrane, and the stage amplification effect of the ion selectivity coefficient.

[0008] To achieve its objectives, the present invention employs the following technical solution:

[0009] This invention first discloses a displacement electrodialysis system coupled with ion distillation, characterized in that it includes a displacement electrodialysis membrane stack composed of alternating layers of cation exchange membranes and anion exchange membranes, forming a by-product chamber, a first feed chamber, a main product chamber, and a second feed chamber within the displacement electrodialysis membrane stack; if the first feed chamber and the adjacent by-product chamber are separated by an anion exchange membrane, then the second feed chamber and the adjacent by-product chamber are separated by a cation exchange membrane.

[0010] One or more anion exchange membranes are added between the first raw material chamber and the adjacent by-product chamber, thereby forming one or more anion distillation chambers between the adjacent anion exchange membranes, which sequentially blocks the cations in the by-product chamber to prevent the cations in the by-product chamber from leaking into the first raw material chamber.

[0011] And / or, one or more cation exchange membranes are added between the second raw material chamber and the adjacent by-product chamber, thereby forming one or more cation distillation chambers between the adjacent cation exchange membranes, which sequentially block anions in the by-product chamber to prevent anions in the by-product chamber from leaking into the second raw material chamber.

[0012] This invention further discloses the application of the coupled ion distillation displacement electrodialysis system, characterized in that it is used to recombine cations in a first raw material with anions in a second raw material through ion exchange to obtain the main product, i.e., the target product. Specifically, in the process of obtaining the main product composed of cations in the first raw material and anions in the second raw material through displacement electrodialysis by ion exchange of the first and second raw materials, the purity of the target product is improved by utilizing the coupled ion distillation chamber.

[0013] Furthermore, the cations include, but are not limited to, NH4. + Li + Na + K + 、Rb + Cs + Ag + Zn 2+ Mg 2+ Ca 2+ Ba 2+ Fe 2+ Cu 2+ Mn 2+ Co 2+ Ni 2+ Al 3+ Fe 3+ Cr 3+ Co 3+ Inorganic cations, (The cationic form of amino acids, where R represents different groups), at least one of the following organic cations: quaternary ammonium salt ion, quaternary phosphate salt ion, imidazole salt ion, and pyrrole salt ion; the anion includes, but is not limited to, F. - Cl - ,Br - I - OH - NO3 - ClO3 - MnO4 - HCO3 - H2PO4 - BF4 - PF6 - CO3 2- SO4 2- PO4 3- [Fe(CN)6]2- [Fe(CN)6] 3- Inorganic anions, HCOO - CH3COO- At least one of the following organic anions: (anionic form of amino acids, where R represents different groups).

[0014] The displacement electrodialysis system using coupled ion distillation described in this invention can be used to produce a variety of products, such as lithium salts like LiOH, LiCl, and Li2CO3; potassium salts like K2SO4 and KCl; ammonium salts like NH4HCO3, NH4Cl, and NaNO3; amino acid salts like sodium L-lysine and zinc L-glutamine; and ionic liquids like TAPOH.

[0015] The principle by which this invention can improve product purity lies in:

[0016] The displacement electrodialysis process is limited by the migration rate of the ion exchange membrane, which cannot actually reach 100%, leading to ion leakage and low product purity. This application couples ion distillation with displacement electrodialysis. According to the basic operating mechanism of electrodialysis, displacement electrodialysis typically uses a combination of cation exchange membranes and anion exchange membranes, with the two membranes stacked to form a membrane unit. Repeated stacking of membrane units can increase the material throughput. This invention breaks with the traditional operating mechanism of displacement electrodialysis, arranging ion exchange membranes according to the principle of "same type, same side." Based on the actual ion leakage situation in displacement electrodialysis, the charge type of the leaking ions is determined, and n "same type" ion exchange membranes are sequentially stacked, capable of transporting ions migrating from the feed chamber to the product chamber while blocking ions leaking from the by-product chamber to the feed chamber. By utilizing the high mobility number of ion exchange membranes, and through n-stage selective separation, ions leaking from the by-product chamber to the feed chamber are effectively blocked. Specifically, cations leaking from the by-product chamber to the feed chamber are effectively blocked by multiple anion exchange membranes, and anions leaking from the by-product chamber to the feed chamber are effectively blocked by multiple cation exchange membranes. This enables the preparation of high-purity target products in a coupled system of ion distillation and displacement electrodialysis technologies.

[0017] In practice, the charge type of the ions that need to be blocked, i.e., the charge type of the leaked ions, can be determined based on the ion leakage situation during the actual operation of the displacement electrodialysis and the purity requirements of the target product. Then, ion exchange membranes of the same charge type are used to couple the process with the displacement electrodialysis, thereby improving product purity. For example, when the leaked ions include both negatively and positively charged ions, one or more anion exchange membranes are added between the first raw material chamber and the adjacent by-product chamber, and one or more cation exchange membranes are added between the second raw material chamber and the adjacent by-product chamber. When the leaked ions are negatively charged, only one or more cation exchange membranes need to be added between the second raw material chamber and the adjacent by-product chamber. When the leaked ions are positively charged, only one or more anion exchange membranes need to be added between the first raw material chamber and the adjacent by-product chamber.

[0018] The first raw material is lithium salt Li x M y (Anion is M) x- The second raw material is alkaline solution N(OH). z (Cation is N) z+ The target product is LiOH, and the byproduct is N. x M z For example:

[0019] If the leaked ions include both negatively charged and positively charged ions: Simultaneously install cation exchange membranes and anion exchange membranes to distill the leaked negatively charged and positively charged ions. Then, use lithium salt Li... x M y and alkaline solution N(OH) Z The first and second raw material chambers are respectively added, strong electrolytes are added to the cathode and anode chambers, auxiliary electrolyte solutions are added to each cation and anion distillation chamber, and pure water or auxiliary electrolyte solution is added to the product chamber. Driven by an electric field, the various levels of anion exchange membranes located between the first raw material chamber and the by-product chamber effectively allow the lithium salt from the raw material Li to pass through. x M y anion M x- It also blocks the flow of byproduct N x M z N-cations z+ In each stage of anion distillation chamber, the cation N z+ The cation exchange membranes at each stage are effectively blocked; simultaneously, the cation exchange membranes at each stage, located between the second raw material chamber and the by-product chamber, allow effective permeation of N(OH) from the alkaline solution. z N-cations z+ It also blocks the flow of byproduct N x M z anion M x- In each stage of cation distillation chambers, anions Mx- The lithium hydroxide product is effectively blocked at each stage, thereby improving its purity.

[0020] If the leaked ions are negatively charged: Add a cation exchange membrane to distill the leaked negatively charged ions. Then, use lithium salt Li... x M y and alkaline solution N(OH) Z The electrolyte is added to the first and second feed chambers respectively, a strong electrolyte is added to the cathode and anode chambers, an auxiliary electrolyte solution is added to each cation distillation chamber, and pure water or an auxiliary electrolyte solution is added to the product chamber. Driven by an electric field, the cation exchange membranes at each stage, located between the second feed chamber and the by-product chamber, effectively allow N(OH)2 from the alkaline solution to pass through. z N-cations z+ It also blocks the flow of byproduct N x M z anion M x- In each stage of cation distillation chambers, anions M x- The lithium hydroxide product is effectively blocked at each stage, thereby improving its purity.

[0021] If the leaked ions are positively charged, an anion exchange membrane is added to distill the leaked positively charged ions. The lithium salt Li... x M y and alkaline solution N(OH) Z The first and second raw material chambers are respectively added, strong electrolytes are added to the cathode and anode chambers, auxiliary electrolyte solutions are added to each anion distillation chamber, and pure water or auxiliary electrolyte solutions are added to the product chamber. Driven by an electric field, the various anion exchange membranes located between the first raw material chamber and the by-product chamber effectively allow the lithium salt from the raw material Li to pass through. x M y anion M x- It also blocks the flow of byproduct N x M z N-cations z+ In each stage of anion distillation chamber, the cation N z+ The lithium hydroxide product is effectively blocked at each stage, thereby improving its purity.

[0022] Specifically: Lithium salts include, but are not limited to, common lithium salts extracted from salt lakes, lithium mines, or spent lithium batteries using techniques such as acid leaching or pyrometallurgical processes, including LiCl, Li2SO4, LiNO3, Li3PO4, and Li2CO3. Alkalis include, but are not limited to, commonly used alkalis such as NaOH, KOH, Ca(OH)2, and NH3·H2O.

[0023] Furthermore, the number of distillation stages in the added ion distillation chamber is greater than or equal to one, and the number of ion distillation stages can be freely increased or decreased according to the composition of the system being processed and the processing objectives.

[0024] Furthermore, the added ion exchange membrane can be selected as needed, and the optional membranes include, but are not limited to, monovalent and polyvalent ion membranes, electrofiltration membranes, conventional ion exchange membranes, bipolar membranes, alkaline membranes, proton exchange membranes, alloy membranes, heterogeneous membranes, etc.

[0025] Compared with existing technologies, the beneficial effects of this invention are reflected in:

[0026] This invention breaks the basic operating mechanism of traditional displacement electrodialysis by coupling ion distillation with a displacement electrodialysis system. By utilizing the ion distillation chamber to achieve multiple isolations of leaked ions, it effectively solves the problem of low product purity caused by ion leakage in traditional displacement electrodialysis. Therefore, this invention provides an innovative method for the preparation of high-purity products (such as battery-grade lithium hydroxide), effectively improving product purity, quality, and recovery rate while shortening the production process and reducing production costs. Attached Figure Description

[0027] Figure 1 The membrane stack configuration of the displacement electrodialysis system used in the comparative example;

[0028] Figure 2 The membrane stack configuration of the displacement electrodialysis system with coupled ion distillation used in the examples;

[0029] Figure 3 This is a schematic diagram of the displacement electrodialysis system and process used in the comparative example of the present invention.

[0030] Figure 4 For the comparison example, the main product chamber contains Li + and Na + Schematic diagram of concentration change over time;

[0031] Figure 5 For the comparative example, the OH in the main product chamber - and SO4 2- Schematic diagram of concentration change over time;

[0032] Figure 6 This is a schematic diagram of the coupled ion distillation displacement electrodialysis system and process used in the embodiments of the present invention;

[0033] Figure 7 In the example, Li in the main product chamber + and Na + Schematic diagram of concentration change over time;

[0034] Figure 8In the example, OH in the main product chamber - and SO4 2- Schematic diagram of concentration change over time;

[0035] Figure 9 In the anion distillation chamber of the example, Li + and Na + Schematic diagram of concentration change over time. Detailed Implementation

[0036] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings and examples. The following content is merely illustrative and explanatory of the concept of the present invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, as long as they do not deviate from the inventive concept or exceed the scope defined by the claims, all of which should fall within the protection scope of the present invention.

[0037] The following examples, using lithium sulfate as the first raw material and sodium hydroxide as the second raw material to produce lithium hydroxide, analyze the application method of the displacement electrodialysis system coupled with anion distillation in this invention. The following comparative examples represent displacement electrodialysis without coupled ion distillation.

[0038] Comparative Example 1

[0039] This comparative example uses displacement electrodialysis with uncoupled ion distillation to prepare lithium hydroxide, with the membrane stack configuration as follows: Figure 1 As shown, a schematic diagram of the displacement electrodialysis system and process flow for uncoupled ion distillation is as follows: Figure 3 As shown.

[0040] In a traditional displacement electrodialysis system, anion and cation exchange membranes are arranged alternately to form two raw material chambers and two product chambers. The anions and cations in the two raw material chambers move to the product chambers under the action of an electric field to form two new salts. Taking displacement electrodialysis with lithium sulfate as the first raw material and sodium hydroxide as the second raw material as an example, the main product is lithium hydroxide and the by-product is sodium sulfate. The traditional displacement electrodialysis membrane stack configuration can be divided into three categories: (1) The arrangement sequence of ion exchange membranes can be: anode - "anion exchange membrane - cation exchange membrane - anion exchange membrane - cation exchange membrane" alternating superimposed repeating units - cathode, where the number of repeating units is at least 1, and the chambers formed are arranged in the order of "by-product chamber - first raw material chamber - main product chamber - second raw material chamber" repeating units along the anode to cathode, and an additional by-product chamber adjacent to the second raw material chamber of the last unit is set at the end. The electrode chambers at both ends are connected and also serve as sodium sulfate product chambers. (2) The arrangement of ion exchange membranes can be in the following order: anode - anion exchange membrane - cation exchange membrane - anion exchange membrane - cation exchange membrane alternating superimposed repeating units - anion exchange membrane - cathode, wherein the number of repeating units is at least 1, and the chambers formed are arranged in the following order from anode to cathode: anode chamber - repeating units of "first raw material chamber - main product chamber - second raw material chamber - by-product chamber" - cathode chamber, and the electrode chambers at both ends are connected. (3) The arrangement of ion exchange membranes can be in the following order: anode - anion exchange membrane - cation exchange membrane - anion exchange membrane alternating superimposed repeating units - cation exchange membrane - cathode, wherein the number of repeating units is at least 1, and the chambers formed are arranged in the following order from anode to cathode: anode chamber - repeating units of "main product chamber - second raw material chamber - by-product chamber - first raw material chamber" - cathode chamber, and the electrode chambers at both ends are connected.

[0041] The system comprises a cathode chamber connected to the anode chamber, through which a low-concentration sodium sulfate solution is introduced as a buffer solution; a lithium sulfate solution of a certain concentration is introduced into the first raw material chamber; a low-concentration lithium hydroxide solution is introduced into the main product chamber; and a sodium hydroxide solution of a certain concentration is introduced into the second raw material chamber. Based on this, a peristaltic pump is used to create four circulation pathways for sodium sulfate, lithium sulfate, lithium hydroxide, and sodium hydroxide. Under the influence of an electric field, lithium ions in the lithium sulfate raw material migrate towards the cathode, passing through the cation membrane into the lithium hydroxide product chamber; sulfate ions in the lithium sulfate raw material migrate towards the anode, passing through the anion membrane into the sodium sulfate product chamber; sodium ions in the sodium hydroxide raw material migrate towards the cathode, passing through the cation membrane into the sodium sulfate product chamber; and hydroxide ions in the sodium hydroxide raw material migrate towards the anode, passing through the anion membrane into the lithium hydroxide product chamber.

[0042] In this comparative example, the displacement electrodialysis configuration is the first configuration described above, with two repeating units, including four cation exchange membranes and four anion exchange membranes. Two ruthenium-iridium electrodes are installed on both sides of the displacement electrodialysis system as end plates and current collectors. Commercially available CMB and AMX membranes are used for the ion exchange membranes. The membrane stack configuration is as follows: anode plate - anode chamber (also a by-product chamber) - anion exchange membrane - first feed chamber - cation exchange membrane - main product chamber - anion exchange membrane - second feed chamber - cation exchange membrane - by-product chamber - anion exchange membrane - first feed chamber - cation exchange membrane - main product chamber - second feed chamber - cation exchange membrane - cathode chamber (also a by-product chamber) - cathode plate. The cathode chamber is connected to the anode chamber. A 0.1 mol / L lithium sulfate solution is introduced into the first feed chamber, and a 0.2 mol / L sodium hydroxide solution is introduced into the second feed chamber. A 0.01 mol / L lithium hydroxide solution is introduced into the main product chamber as an auxiliary electrolyte, and a 0.01 mol / L sodium sulfate solution is introduced into the by-product chamber (which also serves as the electrode chamber) as an auxiliary electrolyte.

[0043] The solutions in each membrane stack chamber were circulated in the storage tank for 15 minutes until the liquid levels in each chamber remained constant and the device was running stably. A constant current was then applied to the displacement electrodialysis unit, and the current and voltage changes during operation were monitored online using a power supply. A conductivity meter was used to detect changes in conductivity in each chamber during operation. During operation, samples were periodically taken from the main product chamber, and ICP analysis was performed to detect and analyze the Li in the main product chamber. + Na + and SO4 2- The concentration of OH in the main product chamber was determined by titration. - Concentration, Li + and Na + concentration such as Figure 4 As shown, OH - and SO4 2- concentration Figure 5 As shown.

[0044] Example 1

[0045] This embodiment uses displacement electrodialysis with coupled ion distillation to prepare lithium hydroxide, and the membrane stack configuration is as follows: Figure 2 As shown, the schematic diagram of the displacement electrodialysis system and process of coupled ion distillation is as follows: Figure 6 As shown.

[0046] The displacement electrodialysis system with coupled ion distillation proposed in this invention breaks away from the alternating arrangement of anion and cation exchange membranes. Based on the ion leakage situation in traditional displacement electrodialysis (i.e., ions leaking from the by-product chamber move to the nearest feed chamber under the action of an electric field), one or more ion exchange membranes with the same charge as the leaked ions are selectively added between the by-product chamber and the feed chamber. The principle of mutual repulsion of like charges is used to block the leaked ions step by step, thereby reducing the degree of contamination of the feed chamber.

[0047] Using lithium sulfate as the primary feedstock and sodium hydroxide as the secondary feedstock, the main product is lithium hydroxide, and the byproduct is sodium sulfate. Based on the first type of displacement electrodialysis listed in the comparative example, coupled ion distillation is employed. The displacement electrodialysis membrane stack configurations for coupled ion distillation can be divided into three categories:

[0048] (1) In order to effectively block sodium ions leaking from the by-product sodium sulfate, one or more anion exchange membranes (hereinafter, n represents the number of anion exchange membranes between the by-product chamber and the first raw material chamber) are added between the by-product chamber and the first raw material chamber, i.e., a coupled anion distillation chamber. The arrangement order of the ion exchange membranes is: anode - "anion exchange membrane (×n) - cation exchange membrane - anion exchange membrane - cation exchange membrane" alternating repeating units - cathode, wherein the number of repeating units is at least 1, and the chambers formed are arranged in the following order from anode to cathode: "by-product chamber - anion distillation chamber (×n-1) - first raw material chamber - main product chamber - second raw material chamber" repeating units, and an additional by-product chamber adjacent to the second raw material chamber of the last unit is set at the end. The electrode chambers at both ends are connected and also serve as by-product chambers, through which a low-concentration sodium sulfate solution is introduced as a buffer solution; a low-concentration lithium sulfate solution is introduced as a buffer solution in the anion distillation chamber; a certain concentration of lithium sulfate solution is introduced into the first raw material chamber; a low-concentration lithium hydroxide solution is introduced into the main product chamber; and a certain concentration of sodium hydroxide solution is introduced into the second raw material chamber. Based on this, a peristaltic pump is used to construct circulation pathways for the by-product chamber, the anion distillation chamber (each stage is circulated separately), the first raw material chamber, the second raw material chamber, and the main product chamber.

[0049] (2) To effectively block sulfate ions leaking from the by-product sodium sulfate, one or more cation exchange membranes (hereinafter, m represents the number of cation exchange membranes between the by-product chamber and the second raw material chamber) are added between the by-product chamber and the second raw material chamber, i.e., a coupled cation distillation chamber. The arrangement of the ion exchange membranes is as follows: anode - alternating repeating units of "anion exchange membrane - cation exchange membrane - anion exchange membrane - cation exchange membrane (×m)" - cathode, wherein the number of repeating units is at least 1. The chambers formed are arranged in the following order from anode to cathode: "by-product chamber - first raw material chamber - main product chamber - second raw material chamber - cation distillation chamber (×m-1)" repeating units, and an additional by-product chamber adjacent to the last cation distillation chamber is provided at the end. The electrode chambers at both ends are connected and also serve as by-product chambers, through which a low-concentration sodium sulfate solution is introduced as a buffer solution; a low-concentration lithium hydroxide solution is introduced as a buffer solution in the cation distillation chamber; a certain concentration of lithium sulfate solution is introduced into the first raw material chamber; a low-concentration lithium hydroxide solution is introduced into the main product chamber; and a certain concentration of sodium hydroxide solution is introduced into the second raw material chamber. Based on this, a peristaltic pump is used to construct circulation pathways for the by-product chamber, the cation distillation chamber (each stage is circulated separately), the first raw material chamber, the second raw material chamber, and the main product chamber.

[0050] (3) In order to effectively block sodium ions and sulfate ions leaking from the by-product sodium sulfate, one or more anion exchange membranes are added between the by-product chamber and the first raw material chamber (hereinafter, n represents the number of anion exchange membranes between the by-product chamber and the first raw material chamber), and one or more cation exchange membranes are added between the by-product chamber and the second raw material chamber (hereinafter, m represents the number of cation exchange membranes between the by-product chamber and the second raw material chamber). The arrangement order of the ion exchange membranes is: anode - alternating repeating units of "anion exchange membrane (×n) - cation exchange membrane - anion exchange membrane - cation exchange membrane (×m)" - cathode, wherein the number of repeating units is at least 1, and the chambers formed are arranged in the following order from anode to cathode: "by-product chamber - anion distillation chamber (×n-1) - first raw material chamber - main product chamber - second raw material chamber - cation distillation chamber (×m-1)" repeating units, and an additional by-product chamber adjacent to the cation distillation chamber of the last unit is provided at the end. The electrode chambers at both ends are connected and also serve as by-product chambers, through which a low-concentration sodium sulfate solution is introduced as a buffer solution; a low-concentration lithium sulfate solution is introduced as a buffer solution in the anion distillation chamber; a low-concentration lithium hydroxide solution is introduced as a buffer solution in the cation distillation chamber; a certain concentration of lithium sulfate solution is introduced into the first raw material chamber; a low-concentration lithium hydroxide solution is introduced into the main product chamber; and a certain concentration of sodium hydroxide solution is introduced into the second raw material chamber. Based on this, a peristaltic pump is used to construct circulation pathways for the by-product chamber, the cation distillation chamber (each stage has its own circulation), the anion distillation chamber (each stage has its own circulation), the first raw material chamber, the second raw material chamber, and the main product chamber.

[0051] Considering the comparative example where sodium ion leakage was relatively high and sulfate ion leakage was relatively low, this embodiment selected displacement electrodialysis coupled with anion distillation, i.e., the first scenario described in the above embodiment. The membrane stack includes four cation exchange membranes and six anion exchange membranes, with the anion distillation chamber located between the by-product chamber and the first feed chamber. Two ruthenium-iridium electrodes are installed on both sides of the displacement electrodialysis system as end plates and current collectors. Commercially available CMB and AMX membranes are used for the ion exchange membranes. The arrangement of the ion exchange membranes is as follows: anode - anion exchange membrane - anion exchange membrane - cation exchange membrane - anion exchange membrane - cation exchange membrane - anion exchange membrane - anion exchange membrane - cation exchange membrane - anion exchange membrane - cation exchange membrane - cathode. The resulting chambers, arranged from anode to cathode, are: anode chamber (also serving as a sodium sulfate product chamber) - anion distillation chamber - first feed chamber - main product chamber - second feed chamber - by-product chamber - anion distillation chamber - first feed chamber - main product chamber - second feed chamber - cathode chamber (also serving as a sodium sulfate product chamber).

[0052] The cathode chamber and anode chamber are connected. A 0.1 mol / L lithium sulfate solution is introduced into the first feed chamber, and a 0.2 mol / L sodium hydroxide solution is introduced into the second feed chamber. A 0.01 mol / L lithium hydroxide solution is introduced into the main product chamber as an auxiliary electrolyte, a 0.01 mol / L lithium sulfate solution is introduced into the anion distillation chamber as an auxiliary electrolyte, and a 0.01 mol / L sodium sulfate solution is introduced into the by-product chamber as an auxiliary electrolyte.

[0053] The solutions in each membrane stack chamber were circulated in the storage tank for 15 minutes until the liquid levels in each chamber remained constant and the device was running stably. A constant current was then applied to the coupled ion distillation displacement electrodialysis unit, and the current and voltage changes during operation were monitored online using a power supply. Conductivity meters were used to detect changes in conductivity in each chamber during operation. During operation, samples were periodically taken from the main product chamber and the anion distillation chamber, and ICP analysis was used to detect and analyze the Li in the main product chamber. + Na + and SO4 2- The concentration of Li and the concentration of Li in the anion distillation chamber + and Na + The concentration of OH in the main product chamber was determined by titration. - Concentration. Li in the main product chamber + and Na + concentration such as Figure 7 As shown, OH in the main product chamber - and SO4 2- concentration Figure 8 As shown, Li in the anion distillation chamber + and Na + concentration such as Figure 9 As shown.

[0054] The purity of LiOH (P) LiOH The specific calculation formula is as follows:

[0055]

[0056] in, LiOH product chamber Li + The mass, expressed in μg / L; Na in the LiOH product chamber + The mass, expressed in μg / L; Represents LiOH products in the chamber OH - The mass, expressed in μg / L; Represents SO4 in the LiOH product room 2- The mass, expressed in μg / L;

[0057] To represent Li in LiOH + purity The regulations are as follows:

[0058]

[0059] in, LiOH product chamber Li + The mass, expressed in μg / L; Na in the LiOH product chamber + The mass, expressed in μg / L;

[0060] To represent OH in LiOH - purity (P) OH- The following regulations apply:

[0061]

[0062] in, Represents LiOH products in the chamber OH - The mass, expressed in μg / L; Represents SO4 in the LiOH product room 2- The mass, expressed in μg / L;

[0063] Using the purity calculation formula described above, the purity of Comparative Example 1 and Example 1 at 20 min, 60 min, 100 min, and 140 min of the experiment can be calculated. The calculation results are summarized in Table 1.

[0064] Table 1 Summary of Purity Calculation Results

[0065]

[0066] Comparing displacement electrodialysis systems with and without coupled ion distillation, the above calculations show that in displacement electrodialysis with and without coupled ion distillation... The value consistently exceeds 99.5%, indicating SO4 impurities originating from the byproduct sodium sulfate. 2- The concentration is low and can be ignored; in displacement electrodialysis without coupled ion distillation The concentration has consistently been below 99%, indicating that the impurity Na originates from the byproduct sodium sulfate. + The concentration is high and cannot be ignored; in the displacement electrodialysis system coupled with ion distillation, P LiOH and It increased from less than 99.5% to greater than 99.5%, and from Figure 9 The impurities Na from the byproduct sodium sulfate are clearly visible in the anion distillation chamber. + The increase in concentration indicates that the added ion distillation unit successfully blocked the impurity Na. + .

[0067] The results show that coupling the ion distillation system with displacement electrodialysis breaks the basic operating mechanism of the traditional displacement electrodialysis process, makes full use of the selective series amplification effect of ion distillation, effectively blocks impurity ions from by-products step by step, improves the purity of the main product LiOH, and successfully prepares battery-grade LiOH, proving the feasibility of this displacement electrodialysis system coupled with ion distillation.

[0068] The above are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A displacement electrodialysis system coupled with ion distillation, characterized in that: It includes a displacement electrodialysis membrane stack composed of alternating layers of cation exchange membranes and anion exchange membranes, forming a by-product chamber, a first raw material chamber, a main product chamber, and a second raw material chamber within the displacement electrodialysis membrane stack; if the first raw material chamber and the adjacent by-product chamber are separated by an anion exchange membrane, then the second raw material chamber and the adjacent by-product chamber are separated by a cation exchange membrane. One or more anion exchange membranes are added between the first raw material chamber and the adjacent by-product chamber to form one or more anion distillation chambers, thereby blocking the cations in the by-product chamber step by step to prevent the cations in the by-product chamber from leaking into the first raw material chamber. And / or, one or more cation exchange membranes are added between the second raw material chamber and the adjacent by-product chamber to form one or more cation distillation chambers, thereby blocking anions in the by-product chamber step by step to prevent anions in the by-product chamber from leaking into the second raw material chamber.

2. An application of the displacement electrodialysis system with coupled ion distillation as described in claim 1, characterized in that: It is used to recombine the cations in the first raw material with the anions in the second raw material through ion exchange to obtain the main product.

3. The application according to claim 2, characterized in that: In the process of obtaining the main product composed of cations in the first raw material and anions in the second raw material through ion exchange of the first and second raw materials by displacement electrodialysis, the purity of the target product is improved by using a coupled ion distillation chamber.

4. The application according to claim 2 or 3, characterized in that: The cation is NH4. + Li + Na + K + 、Rb + Cs + Ag + Zn 2+ Mg 2+ Ca 2+ Ba 2+ Fe 2+ Cu 2+ Mn 2+ Co 2+ Ni 2+ Al 3+ Fe 3+ Cr 3+ Co 3+ The anion is at least one of the following: the cationic form of an amino acid, a quaternary ammonium salt ion, a quaternary phosphate salt ion, an imidazole salt ion, and a pyrrole salt ion; - Cl - ,Br - I - OH - NO3 - ClO3 - MnO4 - HCO3 - H2PO4 - BF4 - PF6 - CO3 2- SO4 2- PO4 3- [Fe(CN)6] 2- [Fe(CN)6] 3- HCOO - CH3COO - At least one of the anionic forms of amino acids.

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