Electrochemical reaction device and method for removing impurities from lithium carbonate lithium precipitation mother liquor

Abstract

This invention provides an electrochemical reaction apparatus and method for removing impurities from lithium carbonate mother liquor, belonging to the field of lithium carbonate production technology. The mother liquor is continuously pumped into the electrolyte zone of the anode chamber, overflows through a connecting pipe to the electrolyte zone of the cathode chamber, and is then discharged. The liquid level is controlled to submerge the diaphragm and be higher than the connecting pipe. Electrolysis is performed, and the position of the porous diaphragm is adjusted by raising and lowering it to control ohmic polarization and heat generation. In the anode zone, hydroxyl radicals, persulfate, and chlorine are electrocatalytically generated. Persulfate undergoes pyrolysis to produce sulfate radicals and hydroxyl synergistic oxidation complexes. Chlorine is discharged through the gas collection zone. Residual persulfate in the cathode zone is electroreduced, and the associated hydroxyl radicals continue to oxidize and release carbon dioxide. The carbon dioxide combines with the alkaline environment of the cathode to precipitate calcium and magnesium. This invention utilizes the high temperature of the lithium carbonate production mother liquor, synergistically creating a strong thermal effect within the confined chamber using the diaphragm / porous diaphragm. Combined with the device's self-produced oxidant and precipitant, it improves degradation efficiency without the need for external reagents or heating, achieving simultaneous degradation of complexes and removal of calcium and magnesium. It boasts high impurity removal efficiency and low operating costs.

Description

Technical Field

[0001] This invention belongs to the field of lithium carbonate production technology, specifically relating to an electrochemical reaction device and method for removing impurities from lithium carbonate precipitation mother liquor. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density, long cycle life, and environmental friendliness, have been widely used in electric vehicles, energy storage systems, and portable electronic devices. Battery-grade lithium salt materials (such as lithium carbonate), as key components of cathode materials and electrolytes, are experiencing continuously increasing market demand due to the rapid development of new energy power equipment (such as new energy vehicles, electric ships, and port transport vehicles) and energy storage systems. In the synthesis of cathode materials, lithium carbonate provides the necessary lithium source, reacting with transition metal compounds or precursors such as phosphates through high-temperature solid-state sintering to form a structurally stable and reversibly intercalating / deintercalating lithium active material. Its purity directly determines the overall performance of the final lithium-ion battery.

[0003] In industrial production, metal ion chelating agents are typically introduced into the lithium carbonate crystallization system to complex impurity ions such as calcium and magnesium in the mother liquor, preventing them from precipitating into the product and affecting the purity of lithium carbonate. However, as production continues and the mother liquor is continuously recycled, the chelating agent and chelated ions accumulate in the system, along with chloride ions. These accumulated impurities are difficult to remove effectively using a single method. For example, while conventional advanced oxidation technologies based on persulfate activation and ozone oxidation can degrade organic chelating agents, the introduction of external oxidants makes it difficult to precisely control the oxidation reaction sites, resulting in the inability to effectively regulate the release of calcium and magnesium ions after the chelating agent oxidation. The released free calcium and magnesium ions rapidly combine with newly generated carbon dioxide or existing carbonate ions in the system to form insoluble carbonates that are mixed into the lithium carbonate product. Even after subsequent water washing and high-temperature baking processes, these impurities are difficult to remove, ultimately leading to an increase in the product's impurity content.

[0004] Furthermore, existing lithium carbonate production and purification technologies (such as CN109179458B, CN117446836A, CN117942662A) mostly focus on the separation and purification of downstream processes, and do not yet address the in-situ impurity removal treatment of the lithium carbonate precipitation reaction crystallization system. If conventional advanced oxidation technologies are directly applied to this system, on the one hand, they require external oxidants, leading to increased production costs; on the other hand, the scattering of solid catalysts can easily contaminate the lithium carbonate white product, thus making direct application in the crystallization system impossible. The electrochemical degradation reactors disclosed in existing patent literature (such as CN119638021B, CN121700426A, CN118497787A, CN112752868B) cannot meet the multiple requirements of simultaneously degrading organic matter, chloride ions, and precipitating calcium and magnesium ions under high salt and high temperature conditions. This is due to two main reasons: firstly, the structural design is complex, and secondly, it is difficult to achieve rapid and efficient electrodegradation of complexing agents. Summary of the Invention

[0005] In view of the problems existing in the background art, this application provides an electrochemical reaction device and method for removing impurities from the mother liquor of a lithium carbonate production system.

[0006] To achieve the above objectives, this application adopts the following technical solution: In a first aspect, an electrochemical reaction device for removing impurities from the mother liquor of a lithium carbonate production system is provided, including an electrolytic cell, and a cathode, an anode, a porous partition, a cathode diaphragm, and an anode diaphragm disposed within the electrolytic cell; The porous baffle is vertically and flexibly positioned between the cathode and the anode; The cathode includes a cathode cavity and a cathode electrode disposed within the cathode cavity; The anode includes an anode cavity and an anode electrode disposed within the anode cavity; A cathode diaphragm is provided on the surface of the cathode cavity, and an anode diaphragm is provided on the surface of the anode cavity; The bottom of the anode cavity is provided with a liquid inlet, and the bottom of the cathode cavity is provided with a liquid outlet; The anode cavity and the cathode cavity sidewalls are connected by a connecting pipe; The top of the anode cavity and the top of the cathode cavity are each independently provided with an air inlet and an air outlet.

[0007] In a second aspect, a method for removing impurities from the mother liquor of a lithium carbonate production system is provided, which is carried out using the electrochemical reaction apparatus described in the first aspect, comprising: The lithium carbonate production mother liquor is pumped in through the bottom of the anode chamber, flows through the electrolyte zone in the anode chamber, the connecting pipe between the anode chamber and the cathode chamber, and the electrolyte zone in the cathode chamber, and is then continuously discharged from the bottom of the cathode chamber; the inlet flow rate is controlled to ensure that the electrolyte level is always higher than the connecting pipe and submerges the diaphragm; The power supply is turned on to carry out electrolysis, and the position of the multi-porous baffle is adjusted by lifting and lowering to control the ohmic polarization heat generation, so that the surface of the anode electrode is in a continuous heating state under the combined action of the liquid inlet temperature and the ohmic polarization heat generation. Under the above conditions of electrolysis, heating and continuous liquid feeding, an electrocatalytic oxidation reaction occurs in the mother liquor of the anode chamber, generating hydroxyl radicals, persulfate and chlorine. The persulfate decomposes under high temperature and acidic conditions to produce sulfate radicals and hydroxyl radicals, which oxidize and degrade the complexes in the mother liquor to generate carbon dioxide and / or small molecule organic matter. Some chlorine and some carbon dioxide are discharged from the anode chamber. Some carbon dioxide enters the cathode cavity along with the mother liquor through the connecting pipe. The residual persulfate ions in the mother liquor are decomposed by electroreduction, and the accompanying hydroxyl radicals continue to oxidize the complex and release carbon dioxide. The carbon dioxide, combined with the strongly alkaline environment of the cathode area, precipitates calcium and magnesium impurity ions, and the hydrogen gas produced by the reaction is discharged from the cathode cavity.

[0008] The principle of the electrochemical reactor of this invention is as follows: Utilizing the high temperature (90-95°C) of the lithium carbonate production mother liquor, electrolysis is further performed through a confined space of anode and cathode electrodes. Simultaneously, the electrode polarization is enhanced by the chamber membrane, the porous partition between the anode and cathode, and fluid flow rate control. Vigorous electrolysis (due to the high concentration of the mother liquor) occurs within the electrode chamber, simultaneously generating strong ohmic polarization and heat accumulation. This creates a strongly acidic environment in the anode chamber and a strongly alkaline environment in the cathode, strengthening the degradation of complexes by the anode. Furthermore, the limited electrolysis chambers of the anode and cathode ensure that the solution at the negative electrode is in a state of strong heat accumulation, with the electrode surface temperature higher than that of the bulk solution. On one hand, the inlet temperature of the lithium carbonate production mother liquor reaches 90-95℃. Through ohmic polarization heating, the electrode surface is continuously heated, resulting in a strong near-surface water electrolysis reaction that generates a large number of hydroxyl radicals, which produce a strong nucleophilic reaction with the complexing agent in the solution. Simultaneously, sulfate ions undergo oxidation on the electrode surface to generate persulfate ions. However, due to the high-temperature environment of the electrode surface, some persulfate ions rapidly decompose under acidic conditions, generating sulfate and hydroxyl radicals. These radicals can then be used to strongly oxidize the complexes without relying on the electrode, removing impurities, degrading and mineralizing them to generate small molecules and / or carbon dioxide. Simultaneously, chloride ions can be oxidized at the anode to generate chlorine gas for removal. The reacted solution enters the cathode through a connecting pipe. Under a strongly alkaline environment, the anode gas, after dechlorination, enters the cathode and reacts with calcium and magnesium ions to form precipitates, which are then discharged from the bottom of the chamber with the liquid for filtration. Simultaneously, at the cathode, persulfate is electroreduced to generate sulfate ions, preventing the accumulation of persulfate ions in the lithium carbonate mother liquor. At the same time, hydroxyl radicals continue to oxidize the complexes to generate carbon dioxide, while calcium and magnesium impurity ions are simultaneously precipitated.

[0009] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects: This invention utilizes the high temperature of the lithium carbonate production mother liquor, and further generates a strong thermal effect in a limited chamber through a diaphragm / porous partition. Combined with the oxidant and precipitant produced by the device itself during the electrolysis process, it can not only improve the degradation efficiency and remove complexes in the mother liquor, but also remove calcium and magnesium ions simultaneously. It can also avoid the accumulation of intermediate products (persulfate) in the system without the need for external reagents and heating, achieving simultaneous degradation of complexes and removal of calcium and magnesium. It has high impurity removal efficiency and low operating cost. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 This is a top view schematic diagram of the electrochemical reaction device for removing impurities from the mother liquor of the lithium carbonate production system of the present invention.

[0012] Figure 2 The diagram shows the front view and the cross-sectional view of the anode, where (a) corresponds to the front view and (b) corresponds to the cross-sectional view. Figure 3 The diagram shows the front view and the cross-sectional view of the cathode, where (a) corresponds to the front view and (b) corresponds to the cross-sectional view. Figure 4 This is a schematic diagram of the cathode electrode and the anode electrode, where (a) corresponds to the cathode electrode and (b) corresponds to the anode electrode; Figure 5 The diagrams and exploded views of the anode, anode membrane, porous partition, cathode membrane, and cathode in the electrochemical reaction device are shown, where (a) corresponds to the structural diagram and (b) corresponds to the exploded view. Figure 6 This describes the reaction conditions within the anode chamber. Figure 7 This describes the reaction conditions within the cathode cavity.

[0013] Figure label: 1. Electrolytic cell; 2. Anode; 201. Anode cavity; 202. Anode electrode; 203. Anode guide rod; 204. Anode air inlet; 205. Anode air outlet; 206. Anode liquid inlet; 207. Anode liquid outlet; 3. Liquid inlet pump; 4. Tail gas absorber; 5. Exhaust fan; 6. Cathode; 601. Cathode cavity; 602. Cathode electrode; 603. Cathode guide rod; 604. Cathode air inlet; 605. Cathode air outlet; 606. Cathode liquid inlet; 607. Cathode liquid outlet; 7. Filter; 8. Liquid outlet pump; 9. Porous baffle; 10. Anode diaphragm; 11. Cathode diaphragm; 12. Connecting pipe. Detailed Implementation

[0014] A typical embodiment of the present invention provides an electrochemical reaction device for removing impurities from the mother liquor of a lithium carbonate production system, including an electrolytic cell, and a cathode, an anode, a porous partition, a cathode diaphragm, and an anode diaphragm disposed within the electrolytic cell; The porous baffle can be raised and lowered between the cathode and the anode. The area of ​​the baffle can be adjusted by raising or lowering the baffle, thereby adjusting the ohmic polarization to form heat accumulation in the electrode chamber. The cathode includes a cathode cavity and a cathode electrode disposed within the cathode cavity; The anode includes an anode cavity and an anode electrode disposed within the anode cavity; A cathode diaphragm is provided on the surface of the cathode cavity, and an anode diaphragm is provided on the surface of the anode cavity; The bottom of the anode cavity is provided with a liquid inlet, and the bottom of the cathode cavity is provided with a liquid outlet; The anode cavity and the cathode cavity are connected by a connecting pipe; The top of the anode cavity and the top of the cathode cavity are each independently provided with an air inlet and an air outlet.

[0015] In some preferred embodiments, the anode electrode includes an anode guide rod and an anode electrode body. The anode guide rod is located at the top of the anode electrode body and extends to the outside of the anode cavity to be electrically connected to an external circuit.

[0016] In some preferred embodiments, the anode electrode body is a grid structure; the surface of the grid structure exposed to the electrolyte is coated with an electrocatalytically active coating.

[0017] In some preferred embodiments, the electrocatalytic active coating is a ruthenium-iridium oxide coating or an iridium-tantalum oxide coating.

[0018] In some preferred embodiments, the minimum distance between the surface of the anode electrode body and the surface of the anode diaphragm is 0.5~0.8cm.

[0019] In some preferred embodiments, the anode diaphragm is disposed on both surfaces of the anode cavity or only on one surface of the anode cavity near the cathode cavity.

[0020] In some preferred embodiments, the connecting pipe's ports to the anode cavity and cathode cavity are respectively located at the upper part of the anode cavity and cathode cavity, and correspondingly located on the sidewalls of the anode cavity and cathode cavity, respectively. That is, the upper parts of the anode cavity and cathode cavity are connected by the connecting pipe. The connecting port of the anode cavity is the anode outlet, and the connecting port of the cathode cavity is the cathode inlet. Furthermore, the top of the connecting pipe is lower than the electrolyte surface, ensuring that the connecting pipe is always submerged in the electrolyte during operation. Based on the liquid flow path of bottom inlet and top overflow of the anode cavity, during the upward flow of the mother liquor within the anode cavity, the carbon dioxide generated by the electrochemical reaction is generated in the acidic high-temperature ring of the anode region. The carbon dioxide-rich acidic mother liquor mainly accumulates in dissolved and microbubble states near the upper liquid surface. After overflowing into the cathode cavity through the connecting pipe, it immediately mixes with the strongly alkaline electrolyte in the cathode area. The dissolved carbon dioxide is rapidly converted into carbonate ions and forms carbonate precipitates with calcium and magnesium ions in the mother liquor. Even if some calcium and magnesium ions fail to precipitate completely at the upper liquid surface in the cathode cavity, as the mother liquor continues to flow downward to the bottom outlet area of ​​the cathode cavity, the sufficiently and continuously strong alkaline environment in the cathode area and the oxidation and removal of the complexing agent are enough to ensure that the residual calcium and magnesium ions are almost completely settled when they reach the bottom outlet, thereby achieving continuous and efficient removal of calcium and magnesium impurities in the mother liquor.

[0021] In some preferred embodiments, the anode cavity and the cathode cavity each define an electrolyte region and a gas collecting region sequentially from bottom to top; the main body of the anode electrode is located within the electrolyte region of the anode cavity, and the main body of the cathode electrode is located within the electrolyte region of the cathode cavity. The portion of the cathode conductor of the cathode electrode within the cathode cavity is located in the gas collecting region, and the portion of the anode conductor of the anode electrode within the anode cavity is located in the gas collecting region.

[0022] It should be noted that the anode cavity and cathode cavity are three-dimensional cavities (i.e., all six sides have wall plates) formed by a top wall, a bottom wall, two side walls, and two surfaces. The cathode cavity and the anode cavity have slots on their opposite surfaces. The slots are sealed with electrode diaphragms (cathode diaphragms / anode diaphragms). The interior forms a reaction space for accommodating the electrolyte and electrodes. The anode cavity and the cathode cavity are provided with an air inlet, an air outlet, a liquid inlet, and a liquid outlet that communicate with the internal cavity.

[0023] In some preferred embodiments, the air inlet and outlet of the anode are respectively located on opposite sides of the top of the anode cavity, and the air inlet and outlet of the cathode are respectively located on opposite sides of the top of the cathode cavity.

[0024] In some preferred embodiments, the cathode electrode includes a cathode guide rod and a cathode electrode body. The cathode guide rod is located at the top of the cathode electrode body and extends to the outside of the cathode cavity to be electrically connected to an external circuit.

[0025] In some preferred embodiments, the cathode electrode body is composed of multiple conductive sheets connected to each other by welding.

[0026] In some preferred embodiments, the cathode electrode body is a mesh electrode body; the conductive sheet is a grid structure or a foam metal structure.

[0027] In some preferred embodiments, the conductive sheet is made of titanium, titanium alloy, molybdenum, molybdenum alloy, or stainless steel.

[0028] In some preferred embodiments, the minimum distance between the surface of the cathode electrode body and the surface of the cathode diaphragm is 0.5~0.8cm.

[0029] In some preferred embodiments, the anode membrane and cathode membrane are ceramic membranes, PP membranes, or PTFE hydrophobic membranes.

[0030] In some preferred embodiments, the cathode diaphragm is disposed on both surfaces of the cathode cavity or only on one surface of the cathode cavity near the anode cavity.

[0031] In some preferred embodiments, the area of ​​the porous partition is adjusted by raising or lowering the porous partition.

[0032] In some preferred embodiments, the porous separator is a ceramic separator, a PP separator, or a PTFE hydrophobic separator.

[0033] In some preferred embodiments, the air outlet at the top of the anode cavity is connected to an exhaust fan via a first air outlet pipe.

[0034] In some preferred embodiments, an exhaust gas absorber is provided on the first exhaust pipe.

[0035] In some preferred embodiments, the air outlet at the top of the cathode cavity is connected to an exhaust fan via a second air outlet pipe.

[0036] In some preferred embodiments, the liquid inlet is connected to the liquid inlet pipeline, and the liquid inlet pipeline is equipped with a liquid inlet pump.

[0037] In some preferred embodiments, the liquid outlet is connected to the liquid outlet pipeline, and a filter and a liquid outlet pump are sequentially installed on the liquid outlet pipeline.

[0038] Another typical implementation provides a method for removing impurities from the mother liquor of a lithium carbonate production system, comprising: The lithium carbonate production mother liquor is pumped into the anode chamber through the inlet at the bottom of the anode chamber. After filling the anode chamber from bottom to top, the mother liquor overflows into the cathode chamber through the connecting pipe, and then fills the cathode chamber from bottom to top before being discharged from the outlet at the bottom of the cathode chamber. By controlling the flow rates of the inlet and outlet pumps, the electrolyte level is always kept higher than the height of the connecting pipe, ensuring that the electrolyte is submerged in the cathode and anode diaphragms. The power supply is turned on to apply voltage to the cathode and anode electrodes to carry out electrolysis; at the same time, the position of the porous baffle is adjusted by raising and lowering it to control the ohmic polarization of the cathode and anode electrodes, so that the cathode and anode generate ohmic polarization and heat accumulation effect. The inlet temperature of the lithium carbonate production mother liquor and the ohmic polarization heat generated during the electrolysis process keep the surface of the anode electrode under continuous heating. Under the combined effects of the aforementioned energization, heating, and continuous liquid feeding, the following processes occur in the anode region: Under the action of an electrocatalytic active coating, the surface of the anode electrode catalyzes the electrolysis of water molecules, generating hydroxyl radicals, which undergo nucleophilic reactions with the complexing agents in the mother liquor. Sulfate ions in the mother liquor undergo oxidation on the surface of the anode electrode to generate persulfate ions. Persulfate ions are thermally decomposed in the high-temperature acidic environment on the surface of the anode electrode, generating sulfate radicals and hydroxyl radicals, which carry out strong oxidation reactions on the complexes in the mother liquor that do not depend on the electrode surface. Chloride ions present in the mother liquor are electrocatalytically oxidized to chlorine gas on the surface of the anode electrode. Part of the chlorine gas, part of the carbon dioxide and oxygen are discharged through the anode outlet at the top of the anode cavity and enter the tail gas absorption unit for treatment. The solution entering the cathode chamber from the anode cavity via the connecting pipe undergoes the following process in the cathode region: Carbon dioxide gas entering the cathode with the solution reacts with metal cations in the mother liquor under a strongly alkaline environment to form a precipitate; residual persulfate ions in the cathode chamber undergo an electroreduction reaction on the cathode electrode surface, decomposing into sulfate ions; hydroxyl radicals generated during the cathode reaction oxidize the complex to generate carbon dioxide, and calcium and magnesium impurity ions are simultaneously precipitated; hydrogen gas generated by the cathode reaction is discharged through the cathode outlet at the top of the cathode chamber.

[0039] Specifically, under the action of the electrocatalytically active coating, the surface of the anode electrode undergoes intense electrolysis of water molecules, generating a large number of hydroxyl radicals (·OH), which produce a nucleophilic reaction with the complexing agent in the mother liquor (i.e., the hydroxyl radicals oxidize the complexing agent to generate small organic molecules and / or carbon dioxide); simultaneously, sulfate ions (SO4) in the mother liquor... 2- An oxidation reaction occurs on the surface of the anode electrode to generate persulfate (S₂O₈). 2- Persulfate ions rapidly decompose under high-temperature acidic conditions on the anode electrode surface, generating sulfate free radicals (SO4· ... - ) and hydroxyl radicals (·OH), some free radicals (SO4·- ) and hydroxyl radicals (·OH) perform a strong oxidation reaction on the complexes in the mother liquor, independent of the electrode surface, to remove impurities; chloride ions (Cl) present in the mother liquor - At the anode electrode surface, it is electrochemically oxidized to chlorine gas (Cl2). A small amount of chloride ions participate in the high-temperature homogeneous cracking reaction of persulfate ions to form chlorine free radicals (Cl). Cl2 - The process synergistically enhances the degradation of organic matter; the mother liquor flows from bottom to top in the anode cavity, and the generated chlorine and carbon dioxide move towards the liquid surface. Some of the gas enters the cathode cavity with the mother liquor, while some of the gas (chlorine and carbon dioxide) and oxygen flow through the gas collection area in the anode cavity and are discharged through the anode outlet at the top of the anode cavity and enter the tail gas absorption unit for treatment.

[0040] The solution after the anodic reaction enters the cathode chamber through a connecting pipe. In the strongly alkaline environment of the cathode chamber, carbon dioxide and calcium ions (Ca) from the mother liquor react with the mother liquor as it enters the cathode chamber. 2+ ), magnesium ions (Mg 2+ The cations react to form a precipitate; simultaneously, the residual persulfate ions in the cathode chamber undergo an electroreduction reaction on the cathode electrode surface, decomposing into sulfate ions (SO4). 2- To prevent the accumulation of persulfate ions in the mother liquor, the hydroxyl radicals (·OH) generated during the cathode reaction continue to oxidize the complex to generate carbon dioxide (CO2). The carbon dioxide reacts with calcium and magnesium ions to simultaneously precipitate calcium and magnesium impurities. The hydrogen gas (H2) generated during the cathode reaction flows through the gas collection area of ​​the cathode cavity and is discharged through the cathode outlet at the top of the cathode cavity, and is also introduced into the fresh air exhaust chamber through the cathode inlet to vent the accumulated hydrogen gas. Furthermore, some chlorine gas entering the cathode with the electrolyte generates chloride ions and hypochlorite ions (ClO2) under a strongly alkaline environment. - The free radicals generated during the decomposition of persulfate can form chlorine free radicals (Cl). Cl2 - ,ClO ), and participate synergistically in the degradation reaction of organic matter; the remaining hypochlorite ions are reduced to chloride ions (Cl) at the cathode. - ).

[0041] During electrolysis of the cathode and anode electrodes, the lithium carbonate mother liquor covers the upper end of the electrode cavity diaphragm.

[0042] In some preferred embodiments, the temperature of the lithium carbonate mother liquor is 90~95°C.

[0043] In some preferred embodiments, the treated mother liquor is pumped from the outlet at the bottom of the cathode cavity into a filter via an outlet pump. After filtering to remove the precipitates generated in the reaction, it is returned to the lithium carbonate production system.

[0044] In some preferred embodiments, the electrolysis voltage is 2~60V, for example 2V, 3V, 5V, 10V, 15V, 20V, 25V, 30V, 35V, 40V, 45V, 50V, 55V, 60V, etc.; the electrolysis current density is 1~400A / m 2 For example, 1A / m 2 3A / m 2 5A / m 2 10A / m 2 25A / m 2 50A / m 2 75A / m 2 100A / m 2 150A / m 2 200A / m 2 250A / m 2 300A / m 2 350A / m 2 400A / m 2 .

[0045] In some preferred embodiments, the flow rate of the mother liquor across the surface of the anode electrode is 0.1~20 L / min, for example 0.1 L / min, 0.5 L / min, 1 L / min, 3 L / min, 5 L / min, 8 L / min, 10 L / min, 12 L / min, 15 L / min, 18 L / min, 20 L / min, etc.

[0046] To facilitate understanding of this application, the following description will be more comprehensive and detailed in conjunction with the accompanying drawings and preferred embodiments, but the scope of protection of this application is not limited to the following specific embodiments.

[0047] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of this application.

[0048] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application are available on the market or can be prepared by existing methods.

[0049] Example 1 An electrochemical reaction device for removing impurities from the mother liquor of a lithium carbonate production system is shown in the schematic diagram below. Figure 1 As shown, it includes: Electrolytic cell 1, and anode 2, cathode 6, porous partition 9, cathode diaphragm 11, and anode diaphragm 10 disposed within electrolytic cell 1; the main view and cross-sectional view of anode 2 are shown below. Figure 2 (a) Figure 2 As shown in (b), the main view and cross-sectional view of the cathode 6 are respectively as follows: Figure 3 (a) Figure 3 As shown in (b); The porous partition 9 can be raised and lowered between the anode 2 and the cathode 6. By raising or lowering the porous partition 9, the area of ​​the partition can be adjusted, thereby adjusting the ohmic polarization to form heat accumulation in the electrode chamber. The anode 2 includes an anode cavity 201 and an anode electrode 202 placed inside the anode cavity 201; The cathode 6 includes a cathode cavity 601 and a cathode electrode 602 placed inside the cathode cavity 601; A cathode diaphragm 11 is provided on the surface of the cathode cavity 601 opposite to the anode cavity 201, and an anode diaphragm 10 is provided on the surface of the anode cavity 201 opposite to the cathode cavity 601. The bottom of the anode cavity 201 is provided with an anode inlet 206, and the bottom of the cathode cavity 601 is provided with a cathode outlet 607. The anode cavity 201 and the cathode cavity 601 are connected by a connecting pipe 12, specifically at the side wall position; The top of the anode cavity 201 and the top of the cathode cavity 601 are each independently provided with an anode air inlet 204 / cathode air inlet 604 and an anode air outlet 205 / cathode air outlet 605.

[0050] The anode cavity 201 and cathode cavity 601 are three-dimensional cavities (i.e., all six sides have wall plates) formed by a top wall, a bottom wall, two side walls, and two surfaces. The cathode cavity 601 and the anode cavity 201 have slots on their opposite surfaces. The slots on the surface of the cathode cavity 601 are sealed with a cathode diaphragm 11, and the slots on the surface of the anode cavity 201 are sealed with an anode diaphragm 10. The interior forms a reaction space for accommodating the electrolyte and electrodes. The anode cavity 201 and the cathode cavity 601 are each provided with an air inlet, an air outlet, a liquid inlet, and a liquid outlet that communicate with the internal cavity.

[0051] The anode electrode 202 includes an anode guide rod 203 and an anode electrode body (e.g., ...). Figure 4 (b) As shown, the anode guide rod 203 is located at the top of the anode electrode body and extends to the outside of the anode cavity 201 and is electrically connected to the external circuit; the anode electrode body is a grid structure; the outer surface of the grid structure exposed to the electrolyte is coated with an electrocatalytic active coating; the electrocatalytic active coating is a ruthenium-iridium oxide coating or an iridium-tantalum oxide coating.

[0052] The minimum distance between the surface of the anode electrode body and the surface of the anode diaphragm 10 (i.e., the distance between the opposing surfaces of the anode electrode body and the anode diaphragm 10) is 0.5~0.8cm.

[0053] The anode diaphragm 10 is disposed on both surfaces of the anode cavity 201 or only on one surface of the anode cavity 201 near the cathode cavity 601.

[0054] like Figure 5 As shown, the connection port (anode outlet 207) between the connecting pipe 12 and the anode cavity 201, and the connection port (cathode inlet 606) between the connecting pipe 12 and the cathode cavity 601 are located at the upper part of the anode cavity 201 and the cathode cavity 601, respectively; the top of the connecting pipe 12 is slightly lower than the electrolyte surface to ensure that the electrolyte surface is submerged in the connecting pipe 12.

[0055] The cathode electrode 602 includes a cathode guide rod 603 and a cathode electrode body (e.g., ...). Figure 4 (a) As shown in the figure, the cathode guide rod 603 is located at the top of the cathode electrode body and extends to the outside of the cathode cavity 601 and is electrically connected to the external circuit.

[0056] The cathode electrode body is composed of multiple conductive sheets connected to each other by welding; the cathode electrode body is a mesh electrode body; the conductive sheets are grid structures or foam metal structures.

[0057] The conductive sheet is made of titanium, titanium alloy, molybdenum, molybdenum alloy, or stainless steel.

[0058] The minimum distance between the surface of the cathode electrode body and the surface of the cathode diaphragm 11 (i.e., the distance between the opposing surfaces of the cathode electrode body and the cathode diaphragm 11) is 0.5~0.8cm.

[0059] The cathode diaphragm 11 is disposed on both surfaces of the cathode cavity 601 or only on one surface of the cathode cavity 601 near the anode cavity 201.

[0060] The size of the area of ​​the porous partition 9 is determined by the vertical movement of the porous partition 9. For example, it can also be achieved as follows: a vertically extending guide groove is provided on the inner wall of the electrolytic cell 1, the porous partition 9 slides within the guide groove, and the porous partition 9 is driven by a driving component to move up and down between the cathode 6 and the anode 2. The driving component can be a cylinder, or it can include a motor and a transmission structure. The transmission structure can include a gear and a rack, with the motor connected to the gear and the rack fixedly connected to the porous partition 9, and the gear and rack meshing; alternatively, the transmission structure can include a lead screw and nut, with the motor connected to the lead screw and the nut threaded into the lead screw fixedly connected to the porous partition 9. In laboratory settings, even simpler methods can be used to raise or lower the porous partition 9.

[0061] The porous separator 9 is a ceramic separator, a PP separator, or a PTFE hydrophobic separator.

[0062] The anode outlet 205 at the top of the anode cavity 201 is connected to the exhaust fan 5 through the first exhaust pipe; an exhaust gas absorber 4 is installed on the first exhaust pipe.

[0063] The bottom of the anode cavity 201 is provided with an anode inlet 206, which is connected to the inlet pipeline to realize liquid inlet. The inlet pipeline is provided with an inlet pump 3. The upper side wall of the anode cavity 201 is provided with an anode outlet 207, which is connected to the cathode inlet 606 of the cathode cavity 601 through a connecting pipe 12.

[0064] The cathode outlet 605 at the top of the cathode cavity 601 is connected to the exhaust fan 5 through the second exhaust pipe.

[0065] The upper part of the cathode cavity 601 is provided with a cathode inlet 606, which is connected to the anode outlet 207 through a connecting pipe 12; the bottom of the cathode cavity 601 is provided with a cathode outlet 607, which is connected to an outlet pipeline, and a filter 7 and an outlet pump 8 are sequentially arranged on the outlet pipeline.

[0066] Example 2 A method for removing impurities from the mother liquor of a lithium carbonate production system includes: placing a cathode 6 and an anode 2 in an electrolytic cell 1, and injecting lithium precipitation mother liquor (sulfate concentration of 170 g / L) until its liquid level is slightly higher than the connecting pipe 12 connecting the cathode and anode. The anode inlet 206 is connected to an inlet pump 3, and the outlet pipes of the cathode and anode are connected to a tail gas treatment component, and then to a negative pressure exhaust pipe. The anode diaphragm 10 and cathode diaphragm 11 are made of PP membranes, and the porous partition 9 is made of multi-layered non-woven PP sheet. A fluid pump pumps the mother liquor at a temperature of 90~95℃ into the anode chamber 201. The cathode 6 / anode 2 is connected to a DC power supply, and electrolysis is performed by applying a 3.5V voltage with an electrolysis current of 250A / m.2 The mother liquor is pumped into the anode cavity 201 from the bottom and flows through the electrolyte zone within the anode cavity 201. The flow rate of the mother liquor across the surface of the anode electrode 202 is 1.5 L / min. The reaction conditions within the cathode cavity 601 and the anode cavity 201 are as follows: Figure 6 and Figure 7 As shown. Electro-oxidation (sulfate ions to persulfate ions) and electro-degradation (electrolysis of water to generate hydroxyl radicals oxidize organic complexes) are performed on the surface of the anode electrode 202 under polarized acidic conditions. Sulfate radicals and hydroxyl radicals conduct strong oxidation reactions on the complexes in the mother liquor, independent of the electrode surface. Chloride ions present in the mother liquor are electrocatalytically oxidized to chlorine gas on the surface of the anode electrode 202. The solution, after oxidation on the electrode surface and thermal activation oxidation and degradation by persulfate ions, enters the cathode cavity 601 near the liquid surface along with mixed air bubbles through the connecting pipe 12. Upon entering the cathode cavity 601, the environment becomes alkaline, and the solution flows from near the cathode liquid surface towards the bottom of the electrode. Persulfate ions are electroreduced after passing through the cathode electrode 602, generating free radicals that further oxidize and degrade the organic complexes. The precipitates formed by carbon dioxide and calcium / magnesium ions enter the solid-liquid filter 7 through the bottom pipe along with the solution, and then enter the mother liquor tank. The gases generated by the electrode are absorbed and treated before being discharged. After electrolysis begins, the cathode and anode sides of the electrodes are polarized by the concentration difference of ions due to the action of the anode diaphragm 10 and the cathode diaphragm 11. Ohmic polarization is generated under the action of the anode diaphragm 10, the cathode diaphragm 11 and the porous partition 9, which generates an electrothermal effect on the cathode and anode electrodes, further heating the electrolyte and enhancing the electrode reaction rate. This leads to strong bubble precipitation and aggregation. The bubble walls make ion conduction more difficult, further enhancing the ion concentration difference polarization, which in turn exacerbates the ohmic polarization. Ultimately, a strong electrothermal effect is formed on the electrodes, enhancing the electrolysis reaction and thus forming a synergistic enhanced oxidative degradation effect on the complex.

[0067] In this embodiment, the sampling results during the treatment of the mother liquor are shown in Table 1 below. As can be seen from Table 1, after 1.5 hours of electrolysis, the calcium ion removal rate reached about 95%, and the COD removal rate reached 92.2%.

[0068] Table 1. Component content of the primary sedimentation mother liquor in Example 2 at different electrolysis times. Example 3 A method for removing impurities from mother liquor in a lithium carbonate production system includes: Lithium dioxide mother liquor (sulfate concentration 150 g / L) is injected, ensuring its level is slightly higher than the connecting pipe 12 between the anode and cathode. The anode inlet 206 is connected to the inlet pump 3, and the anode and cathode outlet pipes are connected to the exhaust gas treatment unit, which in turn connects to the negative pressure extraction pipe. The anode diaphragm 10 and cathode diaphragm 11 are made of PP membranes, and the porous partition 9 is made of multi-layered, stacked non-woven PP sheet. A fluid pump pumps the lithium dioxide mother liquor at 90-95℃ into the anode chamber 201. The cathode / anode is connected to a DC power supply, and electrolysis is performed with a 5V voltage and an electrolysis current of 310 A / m. 2 The solution inside the anode is pumped in from the bottom of the anode cavity 201 and flows through the electrolyte zone inside the anode cavity 201. The flow rate of the mother liquor flowing through the surface of the anode electrode 202 is 5 L / min.

[0069] The sampling and testing results of the secondary sedimentation mother liquor are shown in Table 2 below. As can be seen from Table 2, after 1.5h of electrodegradation treatment, the calcium ion removal rate reached about 91.9%, and the COD (chemical oxygen demand) removal rate reached 89.4%.

[0070] Table 2 shows the component content of the secondary precipitation mother liquor at different electrolysis times in Example 3. The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. An electrochemical reaction device for removing impurities from the mother liquor of a lithium carbonate production system, characterized in that, It includes an electrolytic cell, and a cathode, anode, porous partition, cathode diaphragm and anode diaphragm disposed within the electrolytic cell; The porous baffle is vertically and flexibly positioned between the cathode and the anode; The cathode includes a cathode cavity and a cathode electrode disposed within the cathode cavity; The anode includes an anode cavity and an anode electrode disposed within the anode cavity; A cathode diaphragm is provided on the surface of the cathode cavity, and an anode diaphragm is provided on the surface of the anode cavity; The bottom of the anode cavity is provided with a liquid inlet, and the bottom of the cathode cavity is provided with a liquid outlet; The anode cavity and the cathode cavity are connected by a connecting pipe; The top of the anode cavity and the top of the cathode cavity are each independently provided with an air inlet and an air outlet.

2. The electrochemical reaction device for removing impurities from the mother liquor of a lithium carbonate production system as described in claim 1, characterized in that, The anode electrode includes an anode guide rod and an anode electrode body. The anode guide rod is located at the top of the anode electrode body and extends to the outside of the anode cavity to be electrically connected to an external circuit. The anode electrode body is a grid structure; the surface of the grid structure exposed to the electrolyte is coated with an electrocatalytically active coating. The electrocatalytic active coating is a ruthenium-iridium oxide coating or an iridium-tantalum oxide coating; The minimum distance between the surface of the anode electrode body and the surface of the anode diaphragm is 0.5~0.8cm.

3. The electrochemical reaction device for removing impurities from the mother liquor of a lithium carbonate production system as described in claim 2, characterized in that, The connection ports of the connecting pipe to the anode cavity and the cathode cavity are located at the upper part of the anode cavity and the cathode cavity, respectively; the top of the connecting pipe is slightly lower than the electrolyte level; The anode cavity and the cathode cavity each define an electrolyte region and a gas collection region sequentially from bottom to top; the main body of the anode electrode is located within the electrolyte region of the anode cavity; the main body of the cathode electrode is located within the electrolyte region of the cathode cavity. The air inlet and outlet of the anode are respectively located on opposite sides of the top of the anode cavity; the air inlet and outlet of the cathode are respectively located on opposite sides of the top of the cathode cavity.

4. The electrochemical reaction device for removing impurities from the mother liquor of a lithium carbonate production system as described in claim 1, characterized in that, The cathode electrode includes a cathode guide rod and a cathode electrode body; the cathode guide rod is located at the top of the cathode electrode body and extends to the outside of the cathode cavity to be electrically connected to an external circuit; The cathode electrode body is composed of multiple conductive sheets connected to each other by welding. The cathode electrode body is a mesh electrode body; the conductive sheet body is a grid structure or a foam metal structure; The conductive sheet is made of titanium, titanium alloy, molybdenum, molybdenum alloy, or stainless steel. The minimum distance between the surface of the cathode electrode body and the surface of the cathode diaphragm is 0.5~0.8cm.

5. The electrochemical reaction device for removing impurities from the mother liquor of a lithium carbonate production system as described in claim 1, characterized in that, The area of ​​the porous partition is adjusted by raising or lowering the porous partition; And / or, the porous separator is a ceramic separator, a PP separator, or a PTFE hydrophobic separator; And / or, the anode diaphragm is disposed on both surfaces of the anode cavity or only on one surface of the anode cavity near the cathode cavity; And / or, the cathode diaphragm is disposed on both surfaces of the cathode cavity or only on one surface of the cathode cavity near the anode cavity; And / or, the anode diaphragm and cathode diaphragm are ceramic diaphragms, PP diaphragms, or PTFE hydrophobic diaphragms.

6. The electrochemical reaction device for removing impurities from the mother liquor of a lithium carbonate production system as described in claim 1, characterized in that, The air outlet at the top of the anode chamber is connected to the exhaust fan through the first air outlet pipe; An exhaust gas absorber is installed on the first exhaust pipe; And / or, the air outlet at the top of the cathode cavity is connected to the exhaust fan via a second air outlet pipe.

7. The electrochemical reaction device for removing impurities from the mother liquor of a lithium carbonate production system as described in claim 1, characterized in that, The liquid inlet is connected to the liquid inlet pipeline, and the liquid inlet pipeline is equipped with a liquid inlet pump; The outlet is connected to the outlet pipeline, and a filter and an outlet pump are sequentially installed on the outlet pipeline.

8. A method for removing impurities from mother liquor in a lithium carbonate production system, characterized in that, The electrochemical reaction is carried out using the apparatus described in any one of claims 1 to 7, comprising: The lithium carbonate production mother liquor is pumped into the bottom of the anode chamber, flows through the electrolyte zone in the anode chamber, the connecting pipe between the anode chamber and the cathode chamber, and the electrolyte zone in the cathode chamber, and is then continuously discharged from the bottom of the cathode chamber. The inlet and outlet flow rates are controlled to ensure that the electrolyte level is always higher than the connecting pipe and submerges the diaphragm. The power supply is turned on to carry out electrolysis, and the position of the multi-porous baffle is adjusted by lifting and lowering to control the ohmic polarization heat generation, so that the surface of the anode electrode is in a continuous heating state under the combined action of the liquid inlet temperature and the ohmic polarization heat generation. Under the above conditions of electrolysis, heating and continuous liquid feeding, an electrocatalytic oxidation reaction occurs in the mother liquor of the anode chamber, generating hydroxyl radicals, persulfate and chlorine. The persulfate decomposes under high temperature and acidic conditions to produce sulfate radicals and hydroxyl radicals, which oxidize and degrade the complexes in the mother liquor to generate carbon dioxide and / or small molecule organic matter. Some chlorine and some carbon dioxide are discharged from the anode chamber. Some carbon dioxide enters the cathode cavity along with the mother liquor through the connecting pipe. The residual persulfate ions in the mother liquor are decomposed by electroreduction, and the accompanying hydroxyl radicals continue to oxidize the complex and release carbon dioxide. The carbon dioxide, combined with the strongly alkaline environment of the cathode area, precipitates calcium and magnesium impurity ions, and the hydrogen gas produced by the reaction is discharged from the cathode cavity.

9. The method for removing impurities from the mother liquor of a lithium carbonate production system as described in claim 8, characterized in that, The treated mother liquor is pumped from the outlet at the bottom of the cathode cavity into a filter to remove the precipitates generated in the reaction, and then returned to the lithium carbonate production system.

10. The method for removing impurities from the mother liquor of a lithium carbonate production system as described in claim 8, characterized in that, The electrolysis voltage is 2~60V; the electrolysis current density is 1~400A / m 2 ; The flow rate of the mother liquor across the surface of the anode electrode is 0.1~20 L / min.

Images