A migration enhanced ion rectification system and its application in preparation of battery grade lithium hydroxide from salt lake brine

Abstract

The application discloses a migration reinforced ion rectification system and application thereof in preparation of battery-grade lithium hydroxide from salt lake brine, wherein the membrane unit of the system is composed of multiple cation-selective membranes and anion exchange membranes which are stacked according to the principle of'same kind and same side', filled with ion-selective separation resin, and provided with flow channel separators and sealing gaskets. When the migration reinforced ion rectification system is used in preparation of battery-grade lithium hydroxide from salt lake brine, lithium ions and magnesium ions are selectively screened by multiple cation-selective membranes and multiple ion-selective separation resins, and after n-stage selective separation, the selectivity coefficient between lithium ions and magnesium ions is amplified by n stages, lithium ions and hydroxyl ions generated by hydrolysis in the product chamber of the n-stage product chamber generate lithium hydroxide product, and high-efficiency preparation of lithium hydroxide is realized in a single electrodialysis membrane assembly.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of electrically driven membrane separation, and particularly relates to a migration-enhanced ion rectification system and application thereof in preparation of battery-grade lithium hydroxide from salt lake brine. BACKGROUND

[0002] Special ion separation is an important chemical separation technology, and plays an important role in lithium extraction from salt lake. Lithium and its compounds are extremely important energy metals, and are widely used in the fields of electronics, chemical industry, medicine, and nuclear industry. Lithium production in the world has been transferred from lithium ore to brine ore lithium extraction. At present, lithium extraction from salt lake with high magnesium-lithium ratio is still a research difficulty and hotspot.

[0003] Salt lake brine generally contains a high content of calcium and magnesium ions (high magnesium-lithium ratio), and the lithium ion concentration is low. Lithium extraction process generally needs magnesium removal and lithium concentration process. Lithium extraction from salt lake brine needs a complex magnesium removal process, which increases the cost of lithium salt production, and often causes serious environmental pollution in the process.

[0004] Traditionally, the methods for lithium extraction from salt lake brine mainly include precipitation method, evaporation crystallization method, solvent extraction method, calcination leaching method, salting-out method, carbonization method, and ion exchange adsorption method. Among them, the precipitation method and the evaporation crystallization method are relatively mature methods for lithium extraction from salt lake brine. However, these processes still have many problems due to the technical barriers of the processes themselves. For example, the ion exchange process, solvent extraction, and ion sieve adsorption process use the specific interaction between the functional exchange groups or grid framework inside the functional materials and the target ions, and through physical adsorption, selectively screen out the target ions from the complex materials, and then wash out the target ions through the desorption process, so as to realize the separation of the target ions. The separation capacity of the target ions is determined by the adsorption properties of the functional materials themselves, and through the multi-stage integrated coupling between the material adsorption units, the efficient separation of the target ions can be realized. Due to the adsorption and desorption properties of the physical adsorption process during work, they have potential problems such as high cost, environmental pollution, and poor stability in the actual material processing process.

[0005] As an electro-driven membrane separation process, selective electrodialysis can be used in lithium extraction from salt lake. According to the differences in physicochemical properties such as charge properties, hydration energy and ion hydration radius between lithium ions and other impurity ions, by using special functional separators such as a multivalent ion selective membrane, a hydrogen blocking separator and an electric nanofiltration separator, and by using the specific response between lithium ions and the functional separators, there is a certain rate difference between lithium ions and other impurity ions when migrating in the functional separators (usually the migration rate of lithium ions is faster than that of impurity ions), and by using the electric field as the driving force and by using the functional separators in a specific arrangement, the efficient separation of lithium ions can be achieved. As a kind of electrodialysis, the migration-enhanced electrodialysis is coupled with the filling material to further improve the separation performance.

[0006] Similar to traditional special ion separation processes such as ion exchange, solvent extraction and ion sieve adsorption, in industry, multiple selective electrodialysis units need to be coupled and integrated to achieve the target separation of lithium ions, at this time, the continuous operation characteristics of selective electrodialysis cannot be effectively reflected. Therefore, from the aspects of chemical process intensification, efficient separation process and economic process system, the present application breaks the arrangement mode of functional separators in the traditional packed electrodialysis unit, integrates multiple externally coupled packed electrodialysis units, establishes a new migration-enhanced ion rectification technology based on the multi-stage separation mechanism of lithium ions in the functional separators and the series amplification effect of ion selectivity coefficient, and applies it to the lithium extraction process of salt lake brine to achieve one-step extraction of high-purity lithium products from salt lake brine, greatly improving the product purity and extraction efficiency of the salt lake lithium extraction process.

[0007] Compared with the traditional salt lake lithium extraction process, the method of the present application integrates multiple migration-enhanced electrodialysis units, further strengthens the selectivity for target ions, and can accurately separate target ions. The process has the advantages of low energy consumption, high integration, high product purity and environmental friendliness, and has great application potential. SUMMARY

[0008] The present application is to avoid the shortcomings of the above-mentioned existing special ion separation technology, and provides a migration-enhanced ion rectification system, which is used for preparing lithium hydroxide from salt lake brine. By reconfiguring the arrangement mode of functional separators and filling materials in the packed electrodialysis unit, multiple externally coupled migration-enhanced electrodialysis units are integrated to construct a migration-enhanced ion rectification system. Based on the multi-stage separation mechanism of characteristic ions in the functional separators, the series amplification effect of ion selectivity coefficient and the selective adsorption performance of ion selective separation resin, lithium hydroxide products are prepared from high-magnesium-lithium-ratio salt lake brine by one-step method.

[0009] Subject to the basic operation mechanism of electrodialysis process, the electrodialysis is usually selected to use cation special separation diaphragm and anion special separation diaphragm in combination, two diaphragms are stacked to form a membrane unit, and the material processing capacity can be increased by repeatedly stacking the membrane units. The application breaks the basic operation mechanism of the traditional electrodialysis process, arranges the anion functional diaphragm and the cation functional diaphragm according to the'same kind on the same side' principle, uses n'same kind' functional diaphragms by stacking in turn, the target ions are selectively screened by the multiple functional diaphragms in turn, at the same time, the impurity ions are selectively blocked by the multiple functional diaphragms, and the impurity ions are selectively adsorbed by the ion selective separation resin while the target ions pass through, finally, the target ions and the impurity ions are separated by n stages of selective separation, the selectivity coefficient between the target ions and the impurity ions is amplified by stages, so that the efficient separation of the target ions is realized in a single electrodialysis membrane assembly, and the highest target ion separation coefficient of a single membrane separation unit reported so far is achieved.

[0010] The application solves the technical problems by adopting the following technical scheme:

[0011] The application first provides a migration enhanced ion rectification system, which is characterized in that: the migration enhanced ion rectification system comprises a migration enhanced ion rectification device; the migration enhanced ion rectification device is composed of at least one group of migration enhanced ion rectification units packaged between an anode plate and a cathode plate; the migration enhanced ion rectification unit is a membrane unit composed of one or more anion exchange membranes and one or more cation exchange membranes stacked in turn according to the'same kind on the same side' principle, filled with ion selective separation resin, and provided with flow channel separators and sealing gaskets.

[0012] The migration enhanced ion rectification system is a migration enhanced cation rectification system, a migration enhanced anion rectification system or a migration enhanced mixed ion rectification system. When it is a migration enhanced cation rectification system, the ion selective separation resin in the migration enhanced ion rectification unit is filled between adjacent cation exchange membranes. When it is a migration enhanced anion rectification system, the ion selective separation resin in the migration enhanced ion rectification unit is filled between adjacent anion exchange membranes. When it is a migration enhanced mixed ion rectification system, the ion selective separation resin is filled between adjacent cation exchange membranes and between adjacent anion exchange membranes in the migration enhanced ion rectification unit.

[0013] Further, "same type" refers to functional membranes that are selective for the same type of ion, such as anion exchange membranes that are selective for anions, and cation exchange membranes that are selective for cations; "same side" refers to the same type of membrane being placed on the same side, such as the anode side or the cathode side, and different types of functional membranes not being interleaved. The "same type, same side" principle refers to the same type of membrane being placed on the same side, i.e., in the migration-enhanced ion rectification unit, anion exchange membranes are stacked first, then cation exchange membranes are stacked, and the anion exchange membranes are placed close to the anode plate and the cation exchange membranes are placed close to the cathode plate. The membrane unit assembled according to the "same type, same side" principle is an ion rectification unit, and according to different actual operation requirements, a set of ion rectification units can be arranged between the anode plate and the cathode plate, or a plurality of ion rectification units can be arranged repeatedly. According to the screening target of ions, the number of functional membranes used in an ion rectification unit can be freely added or reduced, and the number of "same type" functional membranes can be freely matched, not limited to the "number equivalent" principle.

[0014] Further,

[0015] When it is a migration-enhanced cation rectification system: one or more anion retention chambers are formed between adjacent anion exchange membranes; one or more cation rectification chambers are formed between adjacent cation exchange membranes; a feed liquid chamber is formed between the anion exchange membrane and the cation exchange membrane; ion-selective separation resin is filled in the cation rectification chamber;

[0016] When it is a migration-enhanced anion rectification system: one or more anion rectification chambers are formed between adjacent anion exchange membranes; one or more cation retention chambers are formed between adjacent cation exchange membranes; a feed liquid chamber is formed between the anion exchange membrane and the cation exchange membrane; ion-selective separation resin is filled in the anion rectification chamber;

[0017] When it is a migration-enhanced mixed ion rectification system: one or more anion rectification chambers are formed between adjacent anion exchange membranes; one or more cation rectification chambers are formed between adjacent cation exchange membranes; a feed liquid chamber is formed between the anion exchange membrane and the cation exchange membrane; ion-selective separation resin is filled in the anion rectification chamber and the cation rectification chamber.

[0018] Further, in order to avoid the influence of electrode chamber on the ion rectification process, an end-capped diaphragm can be arranged between the anode plate, the cathode plate and the migration-enhanced ion rectification unit; the anode plate and the end-capped diaphragm form an anode chamber, and the cathode plate and the end-capped diaphragm form a cathode chamber; the end-capped diaphragm close to the anode plate and the adjacent anion exchange membrane form an anion retention chamber (for migration-enhanced cation rectification system) or an anion rectification chamber (for migration-enhanced anion rectification system or migration-enhanced mixed ion rectification system), and the end-capped diaphragm close to the cathode plate and the adjacent cation exchange membrane form a cation retention chamber (for migration-enhanced anion rectification system) or a cation rectification chamber (for migration-enhanced cation rectification system or migration-enhanced mixed ion rectification system).

[0019] The migration-enhanced ion rectification system further comprises a solution auxiliary circulation system and an electric current power supply system; the solution auxiliary circulation system comprises a peristaltic pump for driving solution circulation, a container for storing solution, and a pump pipe for connecting the ion rectification device and the container; the electric current power supply system comprises a constant current or constant voltage power supply, and the anode plate and the cathode plate are connected to the positive electrode and the negative electrode of the constant current or constant voltage power supply, respectively. The anode chamber is connected to an anode liquid storage tank, the cathode chamber is connected to a cathode liquid storage tank, the feed liquid chamber is connected to a feed liquid storage tank, the cation chamber (cation retention chamber or cation rectification chamber) is connected to a cation chamber storage tank, and the anion chamber (anion retention chamber or anion rectification chamber) is connected to an anion chamber storage tank. The solutions in the anode chamber, the cathode chamber, the feed liquid chamber, the cation chamber and the anion chamber are respectively driven by a driving pump to form a circulating flow between the migration-enhanced ion rectification unit and the corresponding storage tank. The driving pump can be any form of diaphragm pump, peristaltic pump, centrifugal pump, submersible pump, piston pump, etc.

[0020] Further, in the migration-enhanced cation rectification system, a special cation exchange membrane with cation selective screening performance and any anion exchange membrane are selected, an ion selective separation resin with cation selective adsorption performance is selected, and the coupling of the ion selective separation resin and the special cation exchange membrane is used to realize the step-by-step screening of cations. In the migration-enhanced anion rectification system, a special anion exchange membrane with anion selective screening performance and any cation exchange membrane are selected, an ion selective separation resin with anion selective adsorption performance is selected, and the coupling of the ion selective separation resin and the special anion exchange membrane is used to realize the step-by-step screening of anions. In the migration-enhanced mixed ion rectification system, a special anion exchange membrane with anion selective screening performance and a special cation exchange membrane with cation selective screening performance are selected, an ion selective separation resin with anion selective adsorption performance and an ion selective separation resin with cation selective adsorption performance are selected, and the coupling of the ion selective separation resin and the corresponding special ion exchange membrane is used to realize the step-by-step screening of anions and cations.

[0021] The number of stages of the migration-enhanced ion rectification system is determined by the number of special anion (cation) selective membranes used. The number of cation (anion) exchange membranes used can be the same as the number of special anion (cation) selective membranes, or the number can be changed according to actual operation needs.

[0022] Taking the migration-enhanced cation rectification system as an example, when the migration-enhanced cation rectification system adopts n-stage rectification single-unit operation, the migration-enhanced cation rectification unit contains n anion exchange membranes, n special cation selective membranes, and 2 end-sealing diaphragms, which can realize n-stage rectification, n≥1. Specifically, the arrangement order of the membranes is: anode plate, end-sealing diaphragm, gasket grid, anion exchange membrane, gasket grid, …, anion exchange membrane, gasket grid, anion exchange membrane, gasket grid, special cation selective membrane, gasket grid, special cation selective membrane, gasket grid, …, special cation selective membrane, gasket grid, end-sealing diaphragm, cathode plate, and sealed by end plate. The functional diaphragms arranged in order from the anode plate side to the cathode plate side are defined as “1 st anion exchange membrane”, “2 nd anion exchange membrane”, “3 rd anion exchange membrane”, “4 th anion exchange membrane”, …, “n th anion exchange membrane”, “1 st special cation selective membrane”, “2 nd special cation selective membrane”, “3 rd special cation selective membrane”, “4 th"special cation selective membrane", "…", "n th "special cation selective membrane". An anode plate and the adjacent end-capped membrane form an anode chamber; 1 st "anion exchange membrane" and the adjacent end-capped membrane form an n th "anion retention chamber", 1 st "anion exchange membrane" and 2 nd "anion exchange membrane" form an n-1 th "anion retention chamber", …, n-2 th "anion exchange membrane" and n-1 th "anion exchange membrane" form 2 nd "anion retention chamber", n-1 th "anion exchange membrane" and n th "anion exchange membrane" form 1 st "anion retention chamber"; n th "anion exchange membrane" and 1 st "special cation selective membrane" form a feed solution chamber; 1 st "special cation selective membrane" and 2 nd "special cation selective membrane" form 1 st "cation rectification chamber", 2 nd "special cation selective membrane" and 3 rd "special cation selective membrane" form 2 nd "cation rectification chamber", …, n-1 th "special cation selective membrane" and n th "special cation selective membrane" form n-1 th "cation rectification chamber", n th "special cation selective membrane" and the adjacent end-capped membrane form n th "cation rectification chamber"; a cathode plate and the adjacent end-capped membrane form a cathode chamber. In each stage of the cation rectification chamber, ion selective separation resin with cation selective adsorption performance is filled.

[0023] When the cation rectification device adopts n-stage rectification multiple unit operations, the membrane arrangement of each unit is in accordance with the above principles, and the rectification stages of each unit can be the same or different. An end-capped membrane can be added between adjacent units, and the arrangement of the anion retention chamber and the cation rectification chamber in each unit is the same as described above; an end-capped membrane can also not be added between adjacent units, and they are directly stacked, at which time the n th "special cation selective membrane" of the previous unit and the 1 st "anion exchange membrane" of the next unit are adjacent, and they are equivalent to the "end-capped membrane" of each other, and the chamber formed between the two membranes serves as the n th "cation rectification chamber" of the previous unit, and also serves as the n thAnion retention chamber. Increasing the number of repeating units can increase the feed liquid processing capacity of the system.

[0024] The 1 st Cation rectification chamber and 1 st The cation chamber and the anion chamber can be driven by the cation chamber drive pump and the anion chamber drive pump to independently circulate the solution between the separate cation chamber storage tanks and the anion chamber storage tanks, or the solution can be driven by the anion chamber drive pump or the cation chamber drive pump to mix and circulate between the same anion chamber storage tank or cation chamber storage tank; The 1 th Cation rectification chamber and n th The cation chamber and the anion chamber can be driven by the cation chamber drive pump and the anion chamber drive pump to independently circulate the solution between the separate cation chamber storage tanks and the anion chamber storage tanks, or the solution can be driven by the anion chamber drive pump or the cation chamber drive pump to mix and circulate between the same anion chamber storage tank or cation chamber storage tank.

[0025] Based on the above-mentioned migration-enhanced cation rectification system, the present application further provides a method for preparing battery-grade lithium hydroxide from salt lake brine, characterized in that: the migration-enhanced cation rectification system is selected, the cation exchange membrane is a multivalent cation selective membrane, the anion exchange membrane is any anion exchange membrane, the end-capped separator is a bipolar membrane, and the ion-selective separation resin is an ion-selective separation resin with selective adsorption capacity for lithium and magnesium ions.

[0026] In use, the salt lake brine to be treated is added to the feed liquid chamber, strong electrolyte solution is added to the anode chamber and the cathode chamber, and lithium chloride solution is added to the anion retention chamber and the cation rectification chamber as auxiliary electrolyte solution; under the driving of the electric field, lithium ions pass through the multivalent cation selective membrane and the ion-selective separation resin from the feed liquid chamber, while magnesium ions are selectively blocked by the multivalent cation selective membrane and the ion-selective separation resin from the feed liquid chamber, so that lithium ions are enriched in the last-stage cation rectification chamber and combined with the hydroxide ions produced by the hydrolysis of the bipolar membrane to obtain lithium hydroxide.

[0027] For the migration-enhanced cation rectification system with n-stage rectification single repeating unit operation, the feed liquid to be separated is added to the feed liquid storage tank and circulated by the feed liquid drive pump; the strong electrolyte solution is added to the anode liquid storage tank and circulated by the anode liquid drive pump; the strong electrolyte solution is added to the cathode liquid storage tank and circulated by the cathode liquid drive pump; the auxiliary electrolyte solution is added to the 1 st Cation chamber storage tank, 2 nd Cation chamber storage tank, …, n-1 th Cation chamber storage tank, n thCation chamber storage tank, 1 st Cation chamber drive pump, 2 nd Cation chamber drive pump, …, n-1 th Cation chamber drive pump, n th Cation chamber drive pump drives solution circulation flow; auxiliary electrolyte solution is added to 1 st Anion chamber storage tank, 1 nd Anion chamber storage tank, …, n-1 th Anion chamber storage tank, n th Anion chamber storage tank, 1 st Anion chamber drive pump, 2 nd Anion chamber drive pump, …, n-1 th Anion chamber drive pump, n th Anion chamber drive pump drives solution circulation flow;

[0028] When the solution circulation reaches stability, an electric current or voltage is applied to the cation rectification system through the power supply, and the cation rectification operation is completed.

[0029] The migration enhanced cation rectification system can include a single or multiple migration enhanced cation rectification units. Taking a four-stage migration enhanced cation rectification system with a single repeating unit as an example: the corresponding solution is introduced into the corresponding chamber of the corresponding rectification system, and by applying an electric current, the cations in the material move through a multivalent cation exchange membrane and ion-selective separation resin towards the cathode under the push of the anode, and the anions in the material move through the anion exchange membrane towards the anode under the push of the cathode. Due to the migration rate of monovalent lithium ions being greater than that of divalent magnesium ions in a multivalent cation exchange membrane and ion-selective separation resin, under the push of the electric field, the cations continue to penetrate 1 st The selective coefficient between monovalent lithium ions and divalent magnesium ions caused by the different migration rates of a multivalent cation exchange membrane and ion-selective separation resin is α, and the monovalent lithium ions and divalent magnesium ions penetrate 1 st After penetrating a multivalent cation exchange membrane and ion-selective separation resin, monovalent lithium ions and divalent magnesium ions are distributed in a ratio of α (concentration ratio) in 1 st Cation rectification chamber retention; under the continuous push of the electric field, 1 st The ions in the cation rectification chamber will continue to penetrate 2 nd A multivalent cation exchange membrane and ion-selective separation resin, due to the migration rate of monovalent lithium ions being greater than that of divalent magnesium ions in a multivalent cation exchange membrane and ion-selective separation resin, monovalent lithium ions and divalent magnesium ions continue to penetrate 2 nd A multivalent cation exchange membrane, and in 2 nd Cation rectification chamber retention, due to 1 stThe distribution ratio of monovalent lithium ions to divalent magnesium ions in the cation rectification chamber is α (concentration ratio), 2 nd The distribution ratio of monovalent lithium ions to divalent magnesium ions received by the cation rectification chamber is α 2 (concentration ratio); likewise, under the continuous driving effect of the electric field, 2 nd The ions in the cation rectification chamber will continue to penetrate 3 rd The monovalent lithium ions and the divalent magnesium ions continue to penetrate 3 rd The monovalent lithium ions and the divalent magnesium ions continue to penetrate 3 rd The cation rectification chamber retains, because 2 nd The distribution ratio of monovalent lithium ions to divalent magnesium ions in the cation rectification chamber is α 2 (concentration ratio), 3 rd The distribution ratio of monovalent lithium ions to divalent magnesium ions received by the cation rectification chamber is α 3 (concentration ratio); finally, under the continuous driving effect of the electric field, 3 rd The ions in the cation rectification chamber will continue to penetrate 4 th The monovalent lithium ions and the divalent magnesium ions continue to penetrate 4 th The monovalent lithium ions and the divalent magnesium ions continue to penetrate 4 th The cation rectification chamber retains, because 3 rd The distribution ratio of monovalent lithium ions to divalent magnesium ions in the cation rectification chamber is α 3 (concentration ratio), 4 th The distribution ratio of monovalent lithium ions to divalent magnesium ions received by the cation rectification chamber is α 4 (concentration ratio). Based on the selective screening characteristics of the monovalent lithium ions of the monovalent lithium ions and the ion selective separation resin, by layer-by-layer superposition of the monovalent lithium ions and the ion selective separation resin, the monovalent lithium ions can be realized. A series of level screening; accompanied by the selective migration of monovalent lithium ions and divalent magnesium ions in the monovalent lithium ions and the ion selective separation resin, the anions continue to migrate in the anion exchange membrane under the driving of the electric field, and are retained in the corresponding anion retention chamber.

[0030] The distribution ratio of monovalent lithium ion and divalent magnesium ion in different cation rectification chambers described above is theoretically calculated, and due to the difference in the selectivity coefficient of the multivalent cation exchange membrane and ion selective separation resin used in the packed cation rectification system, the distribution ratio of monovalent lithium ion and divalent magnesium ion in different cation rectification chambers deviates from the theoretical value, but the separation of monovalent lithium ion and divalent magnesium ion still follows the cation rectification screening principle described above.

[0031] The migration-enhanced cation rectification system using multiple repeating units has the same operation principle as the migration-enhanced cation rectification system using a single repeating unit; the migration-enhanced cation rectification system using a single stage, two stages, three stages or four stages has the same operation principle as the migration-enhanced cation rectification system using n stages.

[0032] Compared with the prior art, the beneficial effects of the present application are embodied in:

[0033] Compared with the prior art, the beneficial effects of the present application are embodied in:

[0034] The migration-enhanced ion rectification system in the present application has a selectivity of target ions up to millions of levels, can achieve one-step enrichment of target ions, and has simple system structure, easy to scale up, and great application potential.

[0035] The migration-enhanced ion rectification system in the present application has a selectivity of target ions up to millions of levels, can achieve one-step enrichment of target ions, and has simple system structure, easy to scale up, and great application potential. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The four-stage asymmetric cation rectification system and process schematic diagram used in the examples and comparative examples of the present application are shown in the following figure:

[0037] Figure 2 The membrane stack construction schematic diagram of the four-stage asymmetric cation rectification system (lithium ion rectification mechanism) is shown in the following figure:

[0038] Figure 3 The membrane stack construction schematic diagram of the four-stage asymmetric migration-enhanced cation rectification system (lithium ion rectification mechanism) is shown in the following figure:

[0039] Figure 4In Comparative Example 1, a four-stage asymmetric cation distillation system was used to treat Li. + With Mg 2+ When mixing the feed liquid, Li in the first to fourth stage cation distillation chambers + Schematic diagram of concentration change over time;

[0040] Figure 5 In Comparative Example 1, a four-stage asymmetric cation distillation system was used to treat Li. + With Mg 2+ During the mixing of feed solutions, Mg in the first to fourth stage cation distillation chambers 2+ Schematic diagram of concentration change over time;

[0041] Figure 6 In Comparative Example 1, a four-stage asymmetric cation distillation system was used to treat Li. + With Mg 2+ When mixing the liquid, Li + With Mg 2+ Schematic diagram of selection coefficient changing over time;

[0042] Figure 7 The four-stage asymmetric migration-enhanced cation distillation system used in Example 1 to process Li + With Mg 2+ When mixing the feed liquid, Li in the first to fourth stage cation distillation chambers + Schematic diagram of concentration change over time;

[0043] Figure 8 The four-stage asymmetric migration-enhanced cation distillation system used in Example 1 to process Li + With Mg 2+ During the mixing of feed solutions, Mg in the first to fourth stage cation distillation chambers 2+ Schematic diagram of concentration change over time;

[0044] Figure 9 The four-stage asymmetric migration-enhanced cation distillation system used in Example 1 to process Li + With Mg 2+ When mixing the liquid, Li + With Mg 2+ A diagram illustrating how the selection coefficient changes over time. Detailed Implementation

[0045] In order to make the above objectives, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application are described in detail below with reference to the drawings. The following is only an example and description of the concept of the present application, and those skilled in the art can make various modifications or supplements to the described specific embodiments or use similar ways instead, as long as they do not deviate from the concept of the present application or exceed the scope defined by the present claims, which shall belong to the protection scope of the present application.

[0046] This embodiment uses a cation rectification system to process simulated high-magnesium-lithium-ratio salt lake brine. The main components of the simulated brine are lithium ions, magnesium ions and chloride ions. The ion rectification system used is a four-stage asymmetric cation rectification system. The experimental device is shown in Figure 1 The cathode chamber and the anode chamber are connected and the liquid circulation flow is driven by a solution-driven pump. The first-stage anion retention chamber is circulated separately and the circulation flow is driven by a solution-driven pump. The first, second, third and fourth-stage cation rectification chambers are circulated separately and the circulation flow is driven by a solution-driven pump. The four-stage ion rectification system is composed of one anion exchange membrane, four monovalent cation selective membranes and two bipolar membranes. Two ruthenium-iridium electrodes are placed as electrode plates and current collectors on both sides of the ion rectification system. Two bipolar membranes are placed as end-sealing diaphragms near the cathode and anode ends. One anion membrane is arranged near the anode end, and four monovalent cation selective membranes are repeatedly arranged near the cathode end. The functional diaphragm arrangement structure used in this embodiment is shown in Figure 2 ; the effective area of a single membrane and a membrane stack is 21 cm 2 The monovalent cation selective membrane and the anion exchange membrane are CIMS and AMX series ion exchange membranes produced by ASTOM Company in Japan, respectively.

[0047] At the beginning: the chloride ion concentration in the simulated salt lake brine feed solution used is 0.21 mol / L, and the lithium ion and magnesium ion concentrations are 0.01 mol / L and 0.1 mol / L, respectively. The first-stage anion retention chamber circulates 0.01 mol / L lithium chloride solution as auxiliary electrolyte for forming a current path. Similarly, the first, second, third and fourth-stage cation rectification chambers circulate 0.01 mol / L lithium chloride solution as auxiliary electrolyte for forming a current path. The cathode chamber and the anode chamber circulate 0.3 mol / L lithium sulfate as electrode solution.

[0048] After the solution in each chamber was circulated for 10 minutes to confirm that the system was not leaking and to remove air bubbles, a constant current of 0.22 A was applied, and the voltage and current changes across the ion concentration device were monitored online, and the conductivity of each chamber was monitored online. During the experiment, samples of the solution in each chamber were taken every 1 hour, and the ion concentration in each chamber was analyzed using an inductively coupled plasma emission spectrometer (ICP). The results are shown in Tables 1 to 3. Figure 4 , Figure 5 and Figure 6 .

[0049] Example 1

[0050] In this example, the above-described migration-enhanced cation concentration system was used to treat simulated high-magnesium-lithium-ratio salt lake brine. The main components of the simulated brine were lithium ions, magnesium ions, and chloride ions. The migration-enhanced ion concentration system used was a four-stage asymmetric migration-enhanced cation concentration system. The cathode chamber and the anode chamber were connected and the liquid was circulated by a solution-driven pump. The first-stage anion retention chamber was circulated separately and the circulation was driven by a solution-driven pump. The first-, second-, third-, and fourth-stage cation concentration chambers were circulated separately and the circulation was driven by a solution-driven pump. The four-stage ion concentration system consisted of one anion exchange membrane, four monovalent cation-selective membranes, and two bipolar membranes. Two ruthenium-iridium electrodes were used as electrode plates and current collectors and were placed on both sides of the ion concentration system. Two bipolar membranes were placed near the cathode and anode ends as end-sealing diaphragms. One anion membrane was arranged near the anode end, and four monovalent cation-selective membranes were arranged repeatedly near the cathode end. Ion-selective separation resin was filled in the four cation concentration chambers. The functional diaphragm arrangement used in this example is shown in Table 4. Figure 3 ; the effective area of a single membrane and a single electrode of a membrane stack was 21 cm 2 The CIMS and AMX series ion exchange membranes produced by ASTOM Company in Japan were used as the monovalent cation-selective membrane and the anion exchange membrane, respectively. The strong acid type 732 ion-selective separation resin produced by Shanghai Huazhen Technology Co., Ltd. was used as the filling resin.

[0051] Initially, the chloride ion concentration in the simulated salt lake brine used as the feed liquid was 0.21 mol / L, and the lithium ion and magnesium ion concentrations were 0.01 mol / L and 0.1 mol / L, respectively. The first-stage anion concentration chamber circulated 0.01 mol / L lithium chloride solution as an auxiliary electrolyte to form a current path. Similarly, the first-, second-, third-, and fourth-stage cation concentration chambers circulated 0.01 mol / L lithium chloride solution as an auxiliary electrolyte to form a current path. The cathode chamber and the anode chamber circulated 0.3 mol / L lithium sulfate as the electrode liquid.

[0052] The solutions in each chamber were circulated within the ion distillation system for 10 minutes to ensure the system was leak-proof and free of air bubbles. A constant current of 0.22 A was then applied, and the voltage and current changes across the ion distillation apparatus were monitored online. The conductivity and temperature changes in each chamber were also monitored online. During the experiment, solution samples were taken from each chamber every hour, and inductively coupled plasma atomic emission spectrometry (ICP) was used to analyze the changes in ion concentration in each chamber. Specific results are shown in […]. Figure 7 , Figure 8 and Figure 9 .

[0053] After filtration of the enriched distillate from the fourth-stage product chamber, the solution is dried using a vacuum drying oven to obtain lithium hydroxide product.

[0054] The results show that the designed migration-enhanced cation distillation system, utilizing the multi-stage sieving effect of a multivalent cation selective membrane for monovalent cations, the amplification effect of the ion selectivity coefficient, and the selective adsorption performance of the ion-selective separation resin, achieves a lithium-magnesium selectivity exceeding one million even when the lithium-ion concentration is increased to thirteen to fourteen times. The lithium-ion purity in the fourth-stage lithium-ion distillation chamber can reach over 99.7%, suitable for producing battery-grade lithium products. This migration-enhanced cation distillation system achieves efficient sieving of monovalent and divalent cations in a single operation, yielding high-purity lithium hydroxide, with a lithium-ion selectivity far exceeding that of previously reported ion separation processes. Coupled with ion distillation and ion-selective separation resin methods, this shortens the technical route, reduces production costs, and enables the fine sieving of special cations. This helps reduce lithium extraction costs and significantly lowers the production and manufacturing costs of lithium products.

[0055] 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 protection scope of the present invention.

Claims

1. A system for ion rectification by migration enhancement, characterized in that: The migration-enhanced ion rectification system comprises a migration-enhanced ion rectification device; the migration-enhanced ion rectification device is composed of at least one group of migration-enhanced ion rectification units packaged between an anode plate and a cathode plate; the migration-enhanced ion rectification unit is a membrane unit composed of one or more anion exchange membranes and one or more cation exchange membranes stacked in sequence according to the "same type on the same side" principle, filled with ion-selective separation resin, and provided with flow channel separators and sealing gaskets; the "same type on the same side" principle refers to the same type of membrane being placed on the same side, that is, in the migration-enhanced ion rectification unit, the anion exchange membrane is stacked first, then the cation exchange membrane, and the anion exchange membrane is close to the anode plate and the cation exchange membrane is close to the cathode plate; The migration-enhanced ion rectification system is a migration-enhanced cation rectification system, a migration-enhanced anion rectification system, or a migration-enhanced mixed ion rectification system; When it is a migration-enhanced cation rectification system, the ion-selective separation resin in the migration-enhanced ion rectification unit is filled between adjacent cation exchange membranes; When it is a migration-enhanced anion rectification system, the ion-selective separation resin in the migration-enhanced ion rectification unit is filled between adjacent anion exchange membranes; When it is a migration-enhanced mixed ion rectification system, the ion-selective separation resin is filled between adjacent cation exchange membranes and between adjacent anion exchange membranes in the migration-enhanced ion rectification unit.

2. The migration-enhanced ion rectification system according to claim 1, wherein: When it is a migration-enhanced cation rectification system: one or more anion retention chambers are formed between adjacent anion exchange membranes; one or more cation rectification chambers are formed between adjacent cation exchange membranes; a feed liquid chamber is formed between the anion exchange membrane and the cation exchange membrane; and the ion-selective separation resin is filled in the cation rectification chamber; When it is a migration-enhanced anion rectification system: one or more anion rectification chambers are formed between adjacent anion exchange membranes; one or more cation retention chambers are formed between adjacent cation exchange membranes; a feed liquid chamber is formed between the anion exchange membrane and the cation exchange membrane; and the ion-selective separation resin is filled in the anion rectification chamber; When it is a migration-enhanced mixed ion rectification system: one or more anion rectification chambers are formed between adjacent anion exchange membranes; one or more cation rectification chambers are formed between adjacent cation exchange membranes; a feed liquid chamber is formed between the anion exchange membrane and the cation exchange membrane; The ion-selective separation resin is filled in the anion rectification chamber and the cation rectification chamber.

3. The migration-enhanced ion rectification system according to claim 2, wherein: An end-sealing diaphragm is arranged between the anode plate, the cathode plate and the migration-enhanced ion rectification unit; the anode plate and the end-sealing diaphragm form an anode chamber, and the cathode plate and the end-sealing diaphragm form a cathode chamber; the end-sealing diaphragm close to the anode plate and the adjacent anion exchange membrane form an anion retention chamber or an anion rectification chamber, and the end-sealing diaphragm close to the cathode plate and the adjacent cation exchange membrane form a cation retention chamber or a cation rectification chamber.

4. The migratory enhanced ion-rectification system of claim 1, wherein: The migration-enhanced ion rectification system further comprises a solution auxiliary circulation system and a current power supply system; The solution auxiliary circulation system comprises a peristaltic pump for driving solution circulation, a container for storing solution and a pump pipe for connecting the ion rectification device and the container; the current power supply system comprises a constant current or constant voltage power supply, and the anode plate and the cathode plate are connected to the positive electrode and the negative electrode of the constant current or constant voltage power supply, respectively.

5. The migration-enhanced ion rectification system according to claim 2, wherein: In the migration-enhanced cation rectification system, a special cation exchange membrane with cation selective screening performance and any anion exchange membrane are selected, and an ion selective separation resin with cation selective adsorption performance is selected, and the coupling of the ion selective separation resin and the special cation exchange membrane is used to realize the step-by-step screening of cations; In the migration-enhanced anion rectification system, a special anion exchange membrane with anion selective screening performance and any cation exchange membrane are selected, and an ion selective separation resin with anion selective adsorption performance is selected, and the coupling of the ion selective separation resin and the special anion exchange membrane is used to realize the step-by-step screening of anions; In the migration-enhanced mixed ion rectification system, a special anion exchange membrane with anion selective screening performance and a special cation exchange membrane with cation selective screening performance are selected, and an ion selective separation resin with anion selective adsorption performance and an ion selective separation resin with cation selective adsorption performance are selected, and the coupling of the ion selective separation resin and the corresponding special ion exchange membrane is used to simultaneously realize the step-by-step screening of anions and cations.

6. A process for the production of battery grade lithium hydroxide from salt lake brine, characterized by: The migration-enhanced cation rectification system according to any one of claims 1-5 is selected, the cation exchange membrane is a multivalent cation selective membrane, the anion exchange membrane is any anion exchange membrane, the end-sealing diaphragm is a bipolar membrane, and the ion selective separation resin is an ion selective separation resin with selective adsorption capacity for lithium and magnesium ions; In use, the salt lake brine to be treated is added to the feed liquid chamber, strong electrolyte solution is added to the anode chamber and the cathode chamber, and lithium chloride solution is added to the anion retention chamber and the cation rectification chamber as auxiliary electrolyte solution; under the driving of an electric field, lithium ions gradually permeate through the multivalent cation selective membrane and the ion selective separation resin, and magnesium ions are gradually selectively blocked by the multivalent cation selective membrane and the ion selective separation resin, so that lithium ions are enriched in the last-stage cation rectification chamber and combined with hydroxyl ions generated by the hydrolysis of the bipolar membrane to obtain lithium hydroxide.

7. The process for producing battery grade lithium hydroxide from salt lake brine as claimed in claim 6 wherein: The salt lake brine to be treated is pretreated as needed to remove impurities affecting the ion rectification system before being added to the feed liquid chamber.

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