Method for removing impurities from lithium carbonate lithium precipitation mother liquor

Abstract

The application discloses a method for removing impurities from lithium carbonate lithium precipitation mother liquor and belongs to the technical field of lithium carbonate production. In the application, when the lithium precipitation mother liquor flows through the anode side, a "salt-encapsulated water" microenvironment is formed at the anode interface, effectively inhibiting the occurrence of the oxygen evolution side reaction, promoting the oxidation and mineralization of hydroxyl radicals on the organic chelating agent, oxidizing chloride ions into chlorine gas, and oxidizing sulfate radicals into persulfate radicals. When the mother liquor flows to the cathode side, hydroxyl radicals are generated by water reduction, forming a local alkaline environment, and carbon dioxide reacts with metal impurity ions to form carbonate precipitates under the environment, and chlorine gas is partially converted into hypochlorite. The generated hypochlorite and persulfate radicals can further oxidize and decompose the organic chelating agent and its degradation intermediates under the catalytic action when the mother liquor subsequently flows through the catalyst baffle wall and the pipeline with the catalyst layer arranged on the inner wall. The application can realize the synergistic removal of chelating agent degradation, metal impurity precipitation and anion conversion without introducing an external oxidizing agent.

Description

Technical Field

[0001] This invention belongs to the field of lithium carbonate production technology, specifically relating to a 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 impurity ions such as chloride and fluoride 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 mostly focus on the separation and purification of downstream processes (such as CN109179458B, CN117446836A, CN117942662A), 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 cause contamination of the lithium carbonate "white material" product, thus making direct application in the crystallization system impossible. Summary of the Invention

[0005] To address the above problems, the purpose of this invention is to provide a method for removing impurities from lithium carbonate precipitation mother liquor.

[0006] This invention provides a method for removing impurities from lithium carbonate precipitation mother liquor, comprising the following steps: The lithium precipitation mother liquor from the lithium carbonate production system is introduced into the electrochemical oxidation reactor. The mother liquor enters from the feed pipe on the anode side, and after anodic oxidation, it flows out from the cathode side. Then it flows through the catalyst baffle and the strong magnet baffle in sequence, and then enters the discharge pipe with the inner wall loaded with a catalyst layer. Finally, after solid-liquid separation, the clear liquid is returned to the lithium carbonate production system. Among them, the lithium precipitation mother liquor contains organic chelating agent impurities, metal ion impurities, and anionic impurities.

[0007] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects: (1) Synergistic Impurity Removal Effect of Anodic Oxidation and Cathodic Precipitation: In this invention, after the lithium precipitation mother liquor is introduced from the anode side, the hydroxyl radicals generated by the oxidation of water at the anode interface can directly oxidize and mineralize the organic chelating agent in the mother liquor, causing the carboxyl groups in its molecules to undergo decarboxylation and partially mineralize into CO2. At the same time, chloride ion impurities in the mother liquor are electrochemically oxidized into chlorine gas on the anode surface, and sulfate ions are oxidized into persulfate ions. The mother liquor after anodic oxidation continues to flow to the cathode side, where the water at the cathode interface is reduced to generate hydroxide ions, forming a local alkaline environment on the cathode surface. Under this environment, the carbon dioxide generated by the decarboxylation of the chelating agent on the anode side reacts with the metal impurity ions in the mother liquor to generate carbonate precipitates; at the same time, the chlorine microbubbles generated on the anode side are partially converted into hypochlorite ions in the alkaline environment, which together with persulfate ions constitute secondary oxidation active species. The above process makes full use of the components of the mother liquor itself as reactants, and without introducing any external oxidants, the mother liquor continuously completes the multi-step reaction of chelating agent degradation, metal ion precipitation and chloride ion conversion in the same reactor through "anodic oxidation → cathodic precipitation conversion". Therefore, this invention reduces production costs and avoids the introduction of exogenous impurities while achieving the synergistic removal of multiple impurities, significantly improving the impurity removal efficiency.

[0008] (2) Multi-stage catalysis and magnetic field-assisted deep purification effect: In this invention, the mother liquor after cathode side treatment flows sequentially through a catalyst baffle wall, a strong magnet baffle wall, and a pipe with a catalyst layer on its inner wall. First, when the mother liquor flows through the catalyst baffle wall, the transition metal oxide catalyst loaded on the baffle wall can further catalyze and activate the residual persulfate and hypochlorite ions, continuously generating sulfate free radicals and active chlorine species, which oxidize the organic chelating agent and its intermediate degradation products. Subsequently, the mother liquor flows through the strong magnet baffle wall. Under the action of the magnetic field, the generated carbonate precipitate and some paramagnetic organic complexes agglomerate or become magnetized, which is beneficial to subsequent sedimentation and separation. Next, the mother liquor enters the pipe with a catalyst layer on its inner wall. The catalyst layer in the pipe catalyzes and activates the oxidizing species again, deeply oxidizing and mineralizing the residual organic matter, and further promoting the precipitation of metal ions in the form of carbonate precipitates, while excess carbon dioxide escapes in the form of gas. The above process, through multi-stage synergistic cooperation of electrochemical oxidation, barrier catalysis, magnetic field assistance, and pipeline catalysis, extends the removal effect of the chelating agent from the electrode interface to the entire flow path, significantly improving the total removal rate of the chelating agent and the precipitation rate of metal ions such as calcium and magnesium, thereby further enhancing the overall impurity removal effect. Simultaneously, all catalyst layers are fixed to the inner surface of the barrier wall or pipe wall, do not flow with the mother liquor, and will not enter the lithium carbonate production system to cause product contamination, effectively ensuring the purity of the lithium carbonate product.

[0009] (3) Process Integration and Recycling Effect: In this invention, after the above-mentioned treatment, the mother liquor is filtered through solid-liquid separation to remove precipitates such as calcium carbonate and magnesium carbonate. The clear liquor is then directly returned to the pre-precipitation mother liquor mixing tank of the lithium carbonate production system for recycling. This process is simple, easy to integrate with existing lithium carbonate production lines, and does not require changes to the original main production process, making it convenient for industrial implementation. At the same time, this solution effectively avoids the waste of lithium resources and environmental pollution caused by the discharge of precipitated mother liquor, and has good economic and environmental benefits. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the electrochemical oxidation reactor used in this invention.

[0011] Figure 2 This is a schematic cross-sectional view of the electrochemical oxidation reactor used in this invention.

[0012] Figure 3 This is a schematic diagram of the discharge pipe in this invention.

[0013] Figure 4 This is a schematic diagram of the structure of the strong magnetic fluid screen used in this invention.

[0014] Wherein: 1-Container shell, 2-Feed pipe, 3-Anode, 4-Cathode, 5-Catalyst baffle, 6-Strong magnet baffle, 7-Discharge pipe, 8-Gas outlet; 9-Strip strong magnet, 10-Screen; 71-Catalyst layer, 72-Pipe wall, 73-Auxiliary heating layer, 74-Strong magnet layer. Detailed Implementation

[0015] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0016] As mentioned above, the present invention provides a method for removing impurities from lithium carbonate precipitation mother liquor, comprising the following steps: The lithium precipitation mother liquor from the lithium carbonate production system is introduced into the electrochemical oxidation reactor. The mother liquor enters from the feed pipe 2 on the anode side, is oxidized by the anode 3, and flows out from the cathode side. Then it flows through the catalyst baffle 5 and the strong magnet baffle 6 in sequence, and then enters the discharge pipe 7 with the catalyst layer 71 loaded on the inner wall. Finally, after solid-liquid separation, the clear liquid is returned to the lithium carbonate production system. Among them, the lithium precipitation mother liquor contains organic chelating agent impurities, metal ion impurities, and anionic impurities.

[0017] In this invention, after the lithium precipitation mother liquor is introduced from the anode side, the hydroxyl radicals generated by the oxidation of water at the anode 3 interface can directly oxidize and mineralize the organic chelating agent in the mother liquor, causing the carboxyl groups in its molecules to undergo decarboxylation and partially mineralize into CO2. Simultaneously, chloride ion impurities in the mother liquor are electrochemically oxidized to chlorine gas on the surface of anode 3, and sulfate ions are oxidized to persulfate ions. The mother liquor treated by anode 3 continues to flow to the cathode side, where the water at the cathode 4 interface is reduced to generate hydroxide ions, forming a locally alkaline environment on the surface of cathode 4. Under this environment, the carbon dioxide generated by the decarboxylation of the chelating agent on the anode side reacts with metal impurity ions (such as calcium and magnesium ions) in the mother liquor to form carbonate precipitates; simultaneously, the chlorine microbubbles generated on the anode side are partially converted into hypochlorite ions in the alkaline environment, which, together with persulfate ions, constitute secondary oxidizing active species. The above process fully utilizes the components of the mother liquor itself as reactants, allowing the mother liquor to continuously complete the multi-step reactions of chelating agent degradation, metal ion precipitation, and chloride ion conversion within the same reactor through "anodic oxidation → cathodic precipitation conversion" without introducing any external oxidants. Therefore, this invention reduces production costs and avoids the introduction of exogenous impurities while achieving the synergistic removal of multiple impurities, significantly improving the impurity removal efficiency.

[0018] In this invention, the lithium precipitation mother liquor is a high-concentration salt solution system (near or saturated). During the electrochemical oxidation process, a "salt-in-water" interface microenvironment is formed on the surface of anode 3, meaning the activity of free water molecules at the electrode interface is significantly reduced. This microenvironment effectively inhibits the water oxidation oxygen evolution reaction and its accompanying oxygen evolution kinetics at the anode 3 interface, thereby reducing the generation of ineffective oxygen. After the oxygen evolution reaction is inhibited, on the one hand, the ineffective conversion of active oxygen species (such as adsorbed hydroxyl radicals ·OH) on the anode 3 surface to oxygen is reduced, significantly improving their surface coverage and lifetime at the electrode interface, thus enhancing the direct oxidation efficiency of the chelating agent; on the other hand, the oxygen evolution reaction competes with the reaction of sulfate oxidation to persulfate. After the oxygen evolution is inhibited, the current efficiency shifts towards persulfate generation, and the persulfate yield is significantly improved, providing sufficient oxidation precursors for subsequent continuous deep oxidation on the cathode side and the catalyst.

[0019] The mother liquor, after being treated on the cathode side, flows sequentially through the catalyst baffle 5, the strong magnet baffle 6, and the discharge pipe 7, whose inner wall is lined with a catalyst layer 71, achieving multi-stage gradient deep treatment. When the mother liquor flows through the catalyst baffle 5, the transition metal oxide catalyst filled in the baffle further catalyzes and activates residual persulfate and hypochlorite ions, continuously generating sulfate free radicals and active chloride species, deeply oxidizing the residual organic chelating agents and their intermediate degradation products in the mother liquor. When the mother liquor flows through the strong magnet baffle 6, under the action of a strong magnetic field, the already formed carbonate precipitates and some organic complexes agglomerate or become magnetized, which is beneficial for subsequent sedimentation and solid-liquid separation. Furthermore, the strong magnet baffle 6, in conjunction with the strong magnetic fluid screen installed at the tail end of the discharge pipe 7, effectively prevents catalyst particles and magnetic impurities from entering the subsequent lithium carbonate production system, ensuring product purity by preventing catalyst shedding and oxidation product residue. After the mother liquor enters the discharge pipe 7, which has a catalyst layer 71 on its inner wall, the catalyst layer 71 on the inner wall of the pipe further catalyzes and activates oxidizing species, deeply oxidizing and mineralizing residual organic matter, and further promoting the precipitation of metal ions in the form of carbonates. Excess carbon dioxide is discharged as gas through the gas outlet 8 at the top of the reactor. In this invention, another important function of the catalyst baffle 5 and the catalyst layer 71 on the inner wall of the pipe is to rapidly consume persulfate ions. Persulfate ions generated in the electrochemical region of the mother liquor are rapidly activated and consumed as they flow through the catalyst baffle 5 and the catalyst layer 71, effectively reducing the residual accumulation of persulfate ions in the mother liquor and avoiding the risk of secondary pollution caused by its return to the lithium carbonate production system with the mother liquor.

[0020] Furthermore, the electrochemical oxidation reactor in this invention operates at the same temperature as the mother liquor. Throughout the entire process of the mother liquor flowing from the anode side to the cathode side and entering the discharge pipe 7, its own high-temperature environment thermally activates the residual persulfate ions, further enhancing the oxidation capacity of the persulfate ions. This complements the catalytic activation, ensuring the deep mineralization of the organic chelating agent and its intermediate degradation products.

[0021] This invention achieves highly efficient in-situ synergistic removal of impurities from lithium precipitation mother liquor through a multi-mechanism synergistic process involving "anodic oxidation → cathodic precipitation conversion → catalyst baffle catalytic activation → strong magnet baffle magnetic field assistance → deep catalysis in the discharge pipeline → thermal activation enhancement," without introducing any external oxidants. This process is simple, easily integrated with existing lithium carbonate production lines, produces no secondary pollution, and offers significant economic and environmental benefits.

[0022] In some embodiments, the temperature of the lithium precipitation mother liquor is 60~98°C, preferably 85~98°C.

[0023] In the lithium carbonate production system, the mother liquor temperature ranges from 60 to 98°C, with a predominance of 85 to 98°C. This temperature condition, combined with the auxiliary heating layer 73 on the tube wall 72 and the Joule heating effect generated by electrode polarization, creates a significant thermal activation enhancement effect in localized areas of the electrochemical reactor and the catalyst layer pipeline. Under this thermal effect, persulfate ions generated in the anode region and hypochlorite ions converted from chlorine gas can be rapidly activated and decomposed, producing sulfate free radicals and active chlorine species, respectively. These two components synergistically constitute a highly efficient oxidation system for the deep oxidation and mineralization of residual organic chelating agents in the mother liquor. This concentrates the degradation of chelating agents and the precipitation of metal ions in the electrochemical region and localized areas of the catalyst layer, leaving only a small amount of persulfate ions.

[0024] In some embodiments, the organic chelating agent impurity is any one or more of the following compounds, or any one or more of the sodium, lithium and / or ammonium salts corresponding to the following compounds: ethylenediaminetetraacetic acid, 1,2-bis(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid, ethylene glycol bis(2-aminoethyl ether)tetraacetic acid, aminotriacetic acid, diethylenetriaminepentaacetic acid, glutamic acid diacetic acid, methylglycine diacetic acid, iminodisuccinic acid, and ethylenediaminedisuccinic acid.

[0025] In some embodiments, the metal ion impurities are one or more of calcium, magnesium, copper, nickel, cobalt, and zinc.

[0026] In some embodiments, the anionic impurity is one or both of chloride ions and fluoride ions.

[0027] In some embodiments, the main anion in the lithium precipitation mother liquor is sulfate ion.

[0028] In some embodiments, the flow rate of the lithium precipitation mother liquor is 0.005~0.4V / min, including but not limited to: 0.005V / min, 0.01V / min, 0.05V / min, 0.1V / min, 0.2V / min, 0.3V / min, 0.4V / min, etc.; wherein: V represents the reaction volume of the electrochemical oxidation reactor, in L.

[0029] In some embodiments, the anode 3 is one of ruthenium-iridium oxide coated titanium anode, iridium-tantalum oxide coated titanium anode, platinum-plated titanium anode, and boron-doped diamond anode; the cathode 4 is a foamed metal cathode, specifically selected from foamed stainless steel cathode and foamed titanium cathode.

[0030] In some embodiments, the distance between the anode 3 and the cathode 4 is 2~10cm, including but not limited to: 2cm, 3cm, 4cm, 5cm, 6cm, 7cm, 8cm, 9cm, 10cm, etc.; the output voltage of the electrochemical oxidation reactor is 2.5~60V, including but not limited to: 2.5V, 5V, 10V, 20V, 30V, 40V, 50V, 60V, etc.; the output voltage is DC voltage or pulse voltage.

[0031] In the anodizing process of this invention, by controlling the electrode spacing and applied voltage, electrolytic polarization is formed between the electrodes. The Joule heating effect generated during electrode polarization causes a local temperature increase on the electrode surface. This local temperature rise enhances the oxidation activity of active oxygen species at the anode 3 interface on the chelating agent, and also enhances the catalytic activation efficiency of the persulfate ions generated at the anode 3 on the cathode side, thereby forming a thermally driven synergistic enhanced oxidative degradation within the electrolytic region.

[0032] In some embodiments, when the output voltage is a pulse voltage, the duty cycle of the pulse voltage is 1:1 to 1:20.

[0033] In some embodiments, the catalysts used in the catalyst barrier 5 and the catalyst layer 71 are each independently foamed metal supported on transition metal oxides; wherein: the transition metal oxide is selected from one of iron tetroxide, cobalt tetroxide, cobalt ferrite, and nickel ferrite, the foamed metal is selected from one of foamed stainless steel and foamed titanium, and the mass ratio of the transition metal oxide to the foamed metal is 1:(10~100), including but not limited to: 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, 1:100, etc.

[0034] In some embodiments, the method for preparing the catalyst includes the following steps: preparing a slurry by mixing a transition metal oxide with a binder, coating the slurry onto a foamed metal, and drying it to obtain the catalyst; wherein the mass ratio of the transition metal oxide to the binder is (8~40):1, including but not limited to: 8:1, 10:1, 20:1, 30:1, 40:1, etc.

[0035] In some embodiments, the adhesive is one or both of polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF).

[0036] The electrochemical oxidation reactor includes: a container shell 1, on which a feed pipe 2 and a discharge pipe 7 are provided. The feed pipe 2 is located on the anode side of the container shell 1, and the discharge pipe 7 is located on the cathode side of the container shell 1. Along the direction from the feed pipe 2 to the discharge pipe 7, an anode 3, a cathode 4, a catalyst baffle 5, and a strong magnet baffle 6 are sequentially arranged inside the container shell 1. The catalyst baffle 5 and the strong magnet baffle 6 are sequentially arranged downstream of the cathode 4. The inner wall of the discharge pipe 7 is loaded with a catalyst layer 71.

[0037] In some embodiments, the catalyst barrier 5 is composed of a wall support mold and a catalyst filled therein; wherein the thickness of the catalyst barrier 5 is 0.5~3cm, including but not limited to: 0.5cm, 1cm, 1.5cm, 2cm, 2.5cm, 3cm, etc.

[0038] In some embodiments, a catalyst layer 71 is bonded to the inner wall of the discharge pipe 7; wherein the thickness of the catalyst layer is 0.2~1cm, including but not limited to: 0.2cm, 0.3cm, 0.4cm, 0.5cm, 0.6cm, 0.7cm, 0.8cm, 0.9cm, 1cm, etc.

[0039] In some embodiments, the magnetic field strength of the strong magnet barrier 6 is 1~1.5T, including but not limited to: 1T, 1.1T, 1.2T, 1.3T, 1.4T, 1.5T, etc.

[0040] In some embodiments, the outer wall of the discharge pipe 7 is provided with an auxiliary heating layer 73 and a strong magnet layer 74 in a radial direction from the inside to the outside.

[0041] In some embodiments, the length of the discharge pipe 7 is 1 to 3 m.

[0042] In some embodiments, the discharge pipe 7 has an auxiliary heating layer 73 on its outer wall to control the temperature of the internal catalyst layer 71 to be 0.5~5°C higher than that of the lithium precipitation mother liquor; the magnetic field strength of the strong magnet layer 74 is 1~1.5T, including but not limited to: 1T, 1.1T, 1.2T, 1.3T, 1.4T, 1.5T, etc.

[0043] In some embodiments, the top of the electrochemical oxidation reactor is provided with a gas outlet 8, which is used to connect a vacuum pumping and gas absorption device.

[0044] In some embodiments, a strong magnetic fluid screen is installed at the tail end of the discharge pipe 7 to perform solid-liquid separation.

[0045] The schematic diagram of the electrochemical oxidation reactor used in this invention is shown below. Figure 1 and Figure 2 As shown; the electrochemical oxidation reactor includes a container shell 1, inside which are an anode 3 and a cathode 4. The anode 3 is located on the feed side, and the cathode 4 is located on the discharge side. The lithium precipitation mother liquor enters the reactor from the feed pipe 2 on the anode side, and after being oxidized by the anode 3, it flows out from the cathode side. The top of the reactor is provided with a gas outlet 8 for discharging the gas generated during the reaction and for treating the waste gas. Downstream of the cathode 4, a catalyst baffle 5 and a strong magnet baffle 6 are arranged in sequence, that is, the liquid first flows through the cathode 4, and then passes through the catalyst baffle 5 and the strong magnet baffle 6 in sequence. The catalyst baffle 5 is filled with a foam metal catalyst loaded with transition metal oxides for further catalytic degradation of residual organic chelating agent impurities. The strong magnet baffle 6 is provided with a strong magnet for adsorbing the detached magnetic catalyst particles through a magnetic field and for causing carbonate precipitate particles and some organic complexes to agglomerate or magnetize when passing through a magnetic field. The liquid treated by the catalyst baffle 5 and the strong magnet baffle 6 flows out of the reactor through the discharge pipe 7.

[0046] The structural diagram of the discharge pipe 7 is shown below. Figure 3 As shown; the discharge pipe includes a pipe wall 72, the inner wall of which is loaded with a catalyst layer 71. The catalyst layer 71 is the same as or independently selected from foam metal loaded with transition metal oxides as the catalyst material in the catalyst baffle 5; the pipe wall 72 of the discharge pipe 7 is provided with an auxiliary heating layer 73 and a strong magnet layer 74 radially from the inside to the outside, wherein: the auxiliary heating layer 73 is used to control the temperature of the catalyst layer 71 on the inner wall of the pipe to be 0.5~5℃ higher than the lithium precipitation mother liquor in order to maintain catalytic activity; the strong magnet layer 74 is used to provide a magnetic field to further adsorb residual magnetic metal particles flowing through the pipe; a strong magnetic fluid screen is provided at the tail end of the discharge pipe 7.

[0047] A schematic diagram of the structure of the strong magnetic fluid screen is shown below. Figure 4As shown, it includes a screen 10 and a strip-shaped strong magnet 9 fixed on the screen.

[0048] Example 1 In this embodiment, the anode 3 is a ruthenium-iridium oxide coated titanium anode, and the cathode 4 is foamed titanium; the distance between the anode 3 and the cathode 4 is 5 cm.

[0049] The catalyst barrier 5 has a thickness of 2.5 cm; the strong magnet barrier 6 has a thickness of 3 cm and a magnetic field strength of 1.2 T.

[0050] The catalyst is prepared as follows: Fe3O4 and PVDF are mixed at a mass ratio of 15:1, NMP is added, and a slurry with a solid content of 30wt% is prepared. The slurry is uniformly coated onto foamed titanium metal, wherein the mass ratio of Fe3O4 to foamed titanium is 1:10. After drying, the catalyst is obtained.

[0051] The discharge pipe 7 is 3m long, the inner wall catalyst layer 71 is 0.5cm thick, and the outer wall strong magnet layer 74 has a magnetic field strength of 1.4T.

[0052] In this embodiment, the chelating agent in the lithium precipitation mother liquor is sodium ethylenediaminetetraacetate with a concentration of 0.1 g / L; the main cationic impurities are calcium ions and magnesium ions with concentrations of 600 ppm and 200 ppm, respectively; the main anionic impurities are chloride ions with a concentration of 18000 ppm; and the sulfate concentration in the mother liquor is 170 g / L.

[0053] The lithium precipitation mother liquor (at a temperature of 95°C) was introduced into a 200L electrochemical oxidation reactor at a flow rate of 20L / min, and the DC output voltage was adjusted to 30V. The mother liquor first flowed through anode 3, where the chelating agent underwent oxidative degradation on its surface, partially generating carbon dioxide. Simultaneously, chloride ions were oxidized to generate chlorine gas, and a small amount of sulfate ions were oxidized to persulfate ions. The generated gas flowed with the mother liquor through cathode 4, where water was reduced to generate hydroxide ions on its surface, creating a locally alkaline environment. This environment promoted the reaction of carbon dioxide with calcium and magnesium ions in the mother liquor to form calcium carbonate and magnesium carbonate precipitates, while chlorine gas reacted to generate hypochlorite ions.

[0054] Subsequently, the mother liquor passes sequentially through the catalyst baffle 5, the strong magnet baffle 6, and the discharge pipe 7. Under the catalytic action of the catalyst layer 71 on the inner wall of the catalyst baffle 5 and the discharge pipe 7 (the temperature of the catalyst layer 71 on the inner wall of the pipe is controlled by electric heating through the auxiliary heating layer 73 to be 2-3°C higher than that of the lithium precipitation mother liquor), hypochlorite and persulfate ions further oxidize and degrade the residual chelating agent and its degradation products, and promote the further reaction of calcium and magnesium ions to form precipitates. To prevent catalyst particles from entering the mother liquor, the strong magnet baffle 6 and the strong magnet layer 74 in the discharge pipe 7 magnetically adsorb them.

[0055] The treated mother liquor is first subjected to preliminary solid-liquid separation through a strong magnetic fluid screen, then further purified by a filter membrane, and finally returned to the lithium carbonate production system.

[0056] Before the mother liquor was returned to the lithium carbonate production system, it was sampled and tested. The test results were as follows: chelating agent content was 0.032 g / L, calcium content was 52 ppm, magnesium content was 18 ppm, and chlorine content was 5100 ppm.

[0057] Example 2 In this embodiment, the anode 3 is an iridium tantalum oxide coated titanium anode, and the cathode 4 is foamed stainless steel; the distance between the anode 3 and the cathode 4 is 2cm.

[0058] The catalyst barrier 5 has a thickness of 3cm; the strong magnet barrier 6 has a thickness of 3.5cm and a magnetic field strength of 1.3T.

[0059] The catalyst is prepared as follows: cobalt ferrite and PVDF are mixed at a mass ratio of 20:1, NMP is added, and a slurry with a solid content of 35wt% is prepared. The slurry is uniformly coated onto foamed stainless steel, wherein the mass ratio of cobalt ferrite to foamed stainless steel is 1:50. After drying, the catalyst is obtained.

[0060] The discharge pipe 7 is 2m long, the catalyst layer 71 on its inner wall is 0.8cm thick, and the magnetic field strength of the strong magnet layer 74 on its outer wall is 1.45T.

[0061] In this embodiment, the chelating agent in the lithium precipitation mother liquor is diethylenetriaminepentaacetic acid with a concentration of 0.125 g / L; the main cationic impurities are calcium ions and magnesium ions with concentrations of 500 ppm and 95 ppm, respectively; the main anionic impurities are chloride ions with a concentration of 14500 ppm; and the sulfate concentration in the solution is 173 g / L.

[0062] The lithium precipitation mother liquor (at a temperature of 90°C) was introduced into a 200L electrochemical oxidation reactor at a flow rate of 35L / min, with the pulse output voltage adjusted to 60V (pulse voltage duty cycle of 1:10). The mother liquor first flows through anode 3, where the chelating agent undergoes oxidative degradation on the surface of anode 3, partially generating carbon dioxide. Simultaneously, chloride ions are oxidized to generate chlorine gas, and a small amount of sulfate ions are oxidized to persulfate ions. The generated gas flows with the mother liquor through cathode 4, where water is reduced to generate hydroxide ions on the surface of cathode 4, creating a locally alkaline environment. This environment promotes the reaction of carbon dioxide with calcium and magnesium ions in the mother liquor to form calcium carbonate and magnesium carbonate precipitates, while chlorine gas reacts to form hypochlorite ions.

[0063] Subsequently, the mother liquor passes sequentially through the catalyst baffle 5, the strong magnet baffle 6, and the discharge pipe 7. Under the catalytic action of the catalyst layer 71 on the inner wall of the catalyst baffle 5 and the discharge pipe 7 (the temperature of the catalyst layer 71 on the inner wall of the pipe is controlled by electric heating through the auxiliary heating layer 73 to be 1~2℃ higher than that of the lithium precipitation mother liquor), hypochlorite and persulfate ions further oxidize and degrade the residual chelating agent and its degradation products, and promote the further reaction of calcium and magnesium ions to form precipitates. To prevent catalyst particles from entering the mother liquor, the strong magnet baffle 6 and the strong magnet layer 74 in the discharge pipe 7 magnetically adsorb them.

[0064] The treated mother liquor is first subjected to preliminary solid-liquid separation through a strong magnetic fluid screen, then further purified by a filter membrane, and finally returned to the lithium carbonate production system.

[0065] Before the mother liquor was returned to the lithium carbonate production system, it was sampled and tested. The test results were as follows: chelating agent content was 0.025 g / L, calcium content was 38 ppm, magnesium content was 6 ppm, and chlorine content was 4350 ppm.

[0066] Example 3 In this embodiment, the anode 3 is a platinum-plated titanium anode, and the cathode 4 is foamed titanium; the distance between the anode 3 and the cathode 4 is 10cm.

[0067] The catalyst barrier 5 has a thickness of 2cm; the strong magnet barrier 6 has a thickness of 3cm and a magnetic field strength of 1.25T.

[0068] The catalyst is prepared as follows: Cobalt tetroxide and PVDF are mixed at a mass ratio of 35:1, NMP is added, and a slurry with a solid content of 28wt% is prepared. The slurry is uniformly coated onto titanium foam, wherein the mass ratio of cobalt tetroxide to titanium foam is 1:50. After drying, the catalyst is obtained.

[0069] The discharge pipe 7 is 2m long, the catalyst layer 71 on its inner wall is 1cm thick, and the magnetic field strength of the strong magnet layer 74 on its outer wall is 1.3T.

[0070] In this embodiment, the chelating agent in the lithium precipitation mother liquor is sodium aminotriacetate with a concentration of 1.35 g / L; the main cationic impurities are calcium ions and magnesium ions with concentrations of 485 ppm and 115 ppm, respectively; the main anionic impurities are chloride ions with a concentration of 16580 ppm; and the sulfate concentration in the solution is 171 g / L.

[0071] The lithium precipitation mother liquor (at a temperature of 88°C) was introduced into a 200L electrochemical oxidation reactor at a flow rate of 10L / min, and the DC output voltage was adjusted to 20V. The mother liquor first flowed through anode 3, where the chelating agent underwent oxidative degradation on the surface of anode 3, partially generating carbon dioxide. Simultaneously, chloride ions were oxidized to generate chlorine gas, and a small amount of sulfate ions were oxidized to persulfate ions. The generated gas flowed with the mother liquor through cathode 4, where water was reduced to generate hydroxide ions on the surface of cathode 4, creating a localized alkaline environment. This environment promoted the reaction of carbon dioxide with calcium and magnesium ions in the mother liquor to form calcium carbonate and magnesium carbonate precipitates, while chlorine gas reacted to form hypochlorite ions.

[0072] Subsequently, the mother liquor passes sequentially through the catalyst baffle 5, the strong magnet baffle 6, and the discharge pipe 7. Under the catalytic action of the catalyst layer 71 on the inner wall of the catalyst baffle 5 and the discharge pipe 7 (the temperature of the catalyst layer 71 on the inner wall of the pipe is controlled by electric heating through the auxiliary heating layer 73 to be 4-5°C higher than that of the lithium precipitation mother liquor), hypochlorite and persulfate ions further oxidize and degrade the residual chelating agent and its degradation products, and promote the further reaction of calcium and magnesium ions to form precipitates. To prevent catalyst particles from entering the mother liquor, the strong magnet baffle 6 and the strong magnet layer 74 in the discharge pipe 7 magnetically adsorb them.

[0073] The treated mother liquor is first subjected to preliminary solid-liquid separation through a strong magnetic fluid screen, then further purified by a filter membrane, and finally returned to the lithium carbonate production system.

[0074] Before the mother liquor was returned to the lithium carbonate production system, it was sampled and tested. The test results were as follows: chelating agent content was 0.065 g / L, calcium content was 45 ppm, magnesium content was 16 ppm, and chlorine content was 6350 ppm.

[0075] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for removing impurities from lithium carbonate precipitation mother liquor, characterized in that, Includes the following steps: The lithium precipitation mother liquor from the lithium carbonate production system is introduced into the electrochemical oxidation reactor. The mother liquor enters from the feed pipe on the anode side, and after anodic oxidation, it flows out from the cathode side. Then it flows through the catalyst baffle and the strong magnet baffle in sequence, and then enters the discharge pipe with the inner wall loaded with a catalyst layer. Finally, after solid-liquid separation, the clear liquid is returned to the lithium carbonate production system. Among them, the lithium precipitation mother liquor contains organic chelating agent impurities, metal ion impurities, and anionic impurities; The anionic impurity is chloride ion; The main anion in the lithium precipitation mother liquor is sulfate ion; The catalyst used in the catalyst barrier and the catalyst layer are each independently a foam metal loaded with catalytically active components. The catalytically active components are one of iron tetroxide, cobalt tetroxide, cobalt ferrite, and nickel ferrite, and the foam metal is selected from foam stainless steel and foam titanium.

2. The method for removing impurities from lithium carbonate precipitation mother liquor according to claim 1, characterized in that, The temperature of the lithium precipitation mother liquor is 60~98℃; The flow rate of the lithium precipitation mother liquor is 0.005~0.4V / min, where V represents the reaction volume of the electrochemical oxidation reactor in L.

3. The method for removing impurities from lithium carbonate precipitation mother liquor according to claim 1, characterized in that, The organic chelating agent impurity is any one or more of the following compounds, or any one or more of the sodium, lithium and / or ammonium salts corresponding to the following compounds: ethylenediaminetetraacetic acid, 1,2-bis(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid, ethylene glycol bis(2-aminoethyl ether)tetraacetic acid, aminotriacetic acid, diethylenetriaminepentaacetic acid, glutamic acid diacetic acid, methylglycine diacetic acid, iminodisuccinic acid, ethylenediaminedisuccinic acid; The metal ion impurities are one or more of calcium, magnesium, copper, nickel, cobalt, and zinc.

4. The method for removing impurities from lithium carbonate precipitation mother liquor according to claim 1, characterized in that, The anode is one of ruthenium-iridium oxide coated titanium anode, iridium-tantalum oxide coated titanium anode, platinum-plated titanium anode, and boron-doped diamond anode; the cathode is a foamed metal cathode; the foamed metal cathode is selected from foamed stainless steel cathode and foamed titanium cathode. And / or, the distance between the anode and the cathode is 2~10cm; the output voltage of the electrochemical oxidation reactor is 2.5~60V, and the output voltage is DC voltage or pulse voltage.

5. The method for removing impurities from lithium carbonate precipitation mother liquor according to claim 1, characterized in that, The mass ratio of the catalytically active component to the foam metal is 1:(10~100).

6. The method for removing impurities from lithium carbonate precipitation mother liquor according to claim 1, characterized in that, The electrochemical oxidation reactor includes: a container shell, on which a feed pipe and a discharge pipe are provided, the feed pipe being located on the anode side of the container shell and the discharge pipe being located on the cathode side of the container shell; along the direction from the feed pipe to the discharge pipe, an anode, a cathode, a catalyst baffle wall, and a strong magnet baffle wall are sequentially arranged inside the container shell, the catalyst baffle wall and the strong magnet baffle wall being sequentially arranged downstream of the cathode; wherein, a catalyst layer is loaded on the inner wall of the discharge pipe.

7. The method for removing impurities from lithium carbonate precipitation mother liquor according to claim 6, characterized in that, The catalyst barrier is composed of a wall-supporting mold and a catalyst filled therein; wherein the thickness of the catalyst barrier is 0.5~3cm; The magnetic field strength of the strong magnet barrier is 1~1.5T.

8. The method for removing impurities from lithium carbonate precipitation mother liquor according to claim 6, characterized in that, A catalyst layer is bonded to the inner wall of the discharge pipe; wherein the thickness of the catalyst layer is 0.2~1cm; The length of the discharge pipe is 1 to 3 meters.

9. The method for removing impurities from lithium carbonate precipitation mother liquor according to claim 6, characterized in that, The outer wall of the discharge pipe is also provided with an auxiliary heating layer and a strong magnet layer in sequence along the radial direction. The temperature of the internal catalyst layer is controlled to be 0.5~5℃ higher than that of the lithium precipitation mother liquor by an auxiliary heating layer; The magnetic field strength of the strong magnet layer is 1~1.5T.

10. The method for removing impurities from lithium carbonate precipitation mother liquor according to claim 6, characterized in that, The top of the electrochemical oxidation reactor is provided with a gas outlet, which is used to connect to a vacuum pumping and gas absorption device. A strong magnetic fluid screen is installed at the tail end of the discharge pipe, through which solid-liquid separation is performed.

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