Cyclic purification method and system of KCl-LiCl electrolyte

Abstract

The invention discloses a cyclic purification method and a cyclic purification system for a KCl-LiCl electrolyte. The cyclic purification method comprises the following steps: in the process of preparing metal lithium through electrolysis, monitoring the content of each impurity in a metal lithium electrolytic bath, and respectively judging whether the content of an infusible substance, the content of high-potential ions and the content of one or more of low-potential ions reach above corresponding preset treatment threshold values or not; and impurities are removed according to the monitoring result and the priority sequence of the infusible substances, the high-potential ions and the low-potential ions, and then the electrolyte subjected to impurity removal is filtered and transferred to a metal lithium electrolytic cell to be continuously used. According to the method, common impurities in the KCl-LiCl electrolyte can be effectively removed, high production efficiency and low cost are kept, the method is suitable for being applied to a large-scale production environment, the purity of metal lithium can be remarkably improved, and the service life of an electrolytic cell can be prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolyte impurity removal, and in particular to a circulation purification method and system for a KCl-LiCl electrolyte. Background Art

[0002] Lithium metal is a lightweight, high-energy-density material that plays a vital role in the battery industry, especially in lithium-ion batteries and solid-state batteries. With the rapid development of electric vehicles and energy storage systems, the demand for high-quality lithium metal is increasing. The purity of lithium metal directly affects the performance, safety and service life of the battery. At present, the main method for industrial production of lithium metal is to prepare it by electrolyzing LiCl-KCl mixed molten salt. During electrolysis, lithium chloride will decompose to produce lithium metal at the cathode and chlorine gas at the anode.

[0003] The reaction occurring at the two electrodes is:

[0004] Cathode: Li + +e - →Li

[0005] Anode: 2Cl - -2e - →Cl2↑

[0006] During the electrolytic refining of lithium metal, due to the initial purity limit of lithium chloride (LiCl) and potassium chloride (KCl) raw materials, the chemical compatibility of electrolytic cell construction materials and the inevitable side reactions during the electrolysis process, a large amount of impurities accumulate in the lithium metal electrolyte system. These impurities mainly include infusible solid particles, barium (Ba), calcium (Ca), magnesium (Mg), iron (Fe), boron (B) and sulfur (S) and other elements. The presence of these impurities has a significant impact on electrolytic production, which is manifested in the decrease in the purity of lithium metal products, the decrease in the current efficiency of the electrolysis process and the significant shortening of the service life of the electrolytic cell.

[0007] At present, there is little research on the recycling of lithium metal electrolyte LiCl-KC. The main methods used are water dissolution method and dilution method. The disadvantages of these two methods are more obvious. The water dissolution method relies on water as a solvent to dissolve the impurity-rich LiCl-KCl electrolyte, and then guide it to the lithium chloride production line for reprocessing through a complex process flow. Although this process can achieve the initial recovery of the electrolyte, its significant disadvantage is that its processing cycle is long and involves multiple fine chemical steps, resulting in a cumbersome and inefficient overall process. In addition, the high energy consumption and low recovery rate jointly restrict the economic benefits of this method, making it difficult to meet the needs of modern industry for efficient and low-cost recycling technology. The dilution method adopts the strategy of mixing LiCl-KCl electrolyte with high impurity content with similar electrolyte with low impurity content, aiming to reduce the impurity concentration in the system by physical means. Although this method can effectively alleviate the impurity problem in the short term, its fundamental defect is the lack of an effective impurity removal mechanism. As the electrolysis process continues, impurities continue to accumulate in the system, which will eventually seriously affect the purity of the metal lithium, resulting in a decrease in electrolysis efficiency, and then affecting the stability and product quality of the entire electrolysis production line.

[0008] Therefore, it is urgent to find a systematic method that can effectively remove impurities from lithium electrolyte LiCl-KC in order to fully utilize the electrolyte.

[0009] In view of this, the present invention is proposed. Summary of the invention

[0010] The object of the present invention is to provide a circulating purification method and system for KCl-LiCl electrolyte, so as to effectively remove common impurities in KCl-LiCl electrolyte, such as infusible solid particles, barium, calcium, magnesium, iron, nickel, chromium, boron, silicon, sulfate and carbonate, while maintaining high production efficiency and low cost. The method is particularly suitable for application in a large-scale production environment, and can significantly improve the purity of metallic lithium, improve current efficiency and extend the life of the electrolytic cell.

[0011] The present invention is achieved in that:

[0012] In a first aspect, the present invention provides a circulation purification method of a KCl-LiCl electrolyte, comprising:

[0013] S1. In the process of preparing metallic lithium by electrolysis, the contents of infusible materials, high potential ions and low potential ions of the KCl-LiCl electrolyte in the metallic lithium electrolytic cell are monitored, and it is determined whether the content of the infusible materials reaches or exceeds a preset infusible material processing threshold, whether the content of one or more of the high potential ions reaches or exceeds a corresponding preset processing threshold, and whether the content of one or more of the low potential ions reaches or exceeds a corresponding preset processing threshold;

[0014] S2. Remove impurities according to the monitoring results in the order of priority: infusible materials, high potential ions, and low potential ions:

[0015] If the content of infusibles reaches or exceeds the preset infusible treatment threshold, the electrolyte in the metal lithium electrolytic cell is first subjected to multi-stage filtration to remove the infusibles;

[0016] If the content of one or more of the high-potential ions reaches or exceeds the corresponding preset processing threshold, a curing agent is added to the electrolyte for multi-stage filtration to remove infusibles or the electrolyte for which the monitoring result shows that the infusibles are less than the preset infusible processing threshold, so as to remove the high-potential ions;

[0017] If the content of one or more of the low-potential ions reaches or exceeds the corresponding preset processing threshold, an electrolyte for removing infusibles and / or high-potential ions or an electrolyte whose detection results show that the infusibles and high-potential ions are respectively less than the preset infusible processing threshold and the preset processing threshold corresponding to the high-potential ions is introduced into the pre-electrolysis tank for constant-voltage electrolysis to remove the low-potential ions;

[0018] S3. After removing impurities, the electrolyte is filtered and transferred to a metal lithium electrolytic cell for continued use.

[0019] Optionally, the frequency of monitoring the contents of infusible matter, high potential ions and low potential ions in the electrolyte in the metal lithium electrolytic cell is 5 to 20 days per time.

[0020] Optionally, the high potential ions include Ba 2+ and / or Ca 2+ , low potential ions include SO4 2- 、CO3 2- 、SiO3 2- , BO3 3- PO4 3- Mg 2+ , Fe 2+ 、Al 3+ 、Ni 2+ Cr 3+ and Pb 2+ At least one of .

[0021] Optionally, the high potential ions include Ba 2+ and Ca 2+ , low potential ions include at least Mg 2+ , Fe 2+ 、Al 3+ 、Ni 2+ Cr 3+ and Pb 2+ ; Optionally, the high potential ions include Ba 2+ and Ca 2+ , the low potential ions include SO42- 、CO3 2- 、SiO3 2- , BO3 3- PO4 3- Mg 2+ , Fe 2+ 、Al 3+ 、Ni 2+ Cr 3+ and Pb 2+ .

[0022] Optionally, the preset infusible material processing threshold is selected from 0.04wt% to 0.06wt%.

[0023] Optionally, Ba 2+ The corresponding preset processing threshold is selected from 0.25wt% to 0.35wt%.

[0024] Optionally, Ca 2+ The corresponding preset processing threshold is selected from 0.1wt% to 0.14wt%.

[0025] Optionally, Mg 2+ The corresponding preset processing threshold is selected from 0.02wt% to 0.04wt%.

[0026] Optionally, Fe 2+ The corresponding preset processing threshold is selected from 0.008wt% to 0.012wt%.

[0027] Optionally, Al 3+ The corresponding preset processing threshold is selected from 0.008wt% to 0.012wt%.

[0028] Optionally, Ni 2+ The corresponding preset processing threshold is selected from 0.002wt% to 0.004wt%.

[0029] Optionally, Cr 3+ The corresponding preset processing threshold is selected from 0.002wt% to 0.004wt%.

[0030] Optionally, Pb 2+ The corresponding preset processing threshold is selected from 0.002wt% to 0.004wt%.

[0031] Optionally, SO4 2- The corresponding preset processing threshold is selected from 0.01wt% to 0.02wt%.

[0032] Optionally, CO3 2- The corresponding preset processing threshold is selected from 0.008wt% to 0.012wt%.

[0033] Optionally, SiO32- The corresponding preset processing threshold is selected from 0.008wt% to 0.012wt%.

[0034] Optionally, BO3 3- The corresponding preset processing threshold is selected from 0.008wt% to 0.012wt%.

[0035] Optionally, PO4 3- The corresponding preset processing threshold is selected from 0.008wt% to 0.012wt%

[0036] Optionally, the preset infusible material processing threshold is 0.05wt%.

[0037] Optionally, Ba 2+ The corresponding preset processing threshold is 0.3wt%.

[0038] Optionally, Ca 2+ The corresponding preset processing threshold is 0.1 wt %.

[0039] Optionally, Mg 2+ The corresponding preset processing threshold is 0.03wt%.

[0040] Optionally, Fe 2+ The corresponding preset processing threshold is 0.01 wt %.

[0041] Optionally, Al 3+ The corresponding preset processing threshold is 0.01 wt %.

[0042] Optionally, Ni 2+ The corresponding preset processing threshold is 0.003wt%.

[0043] Optionally, Cr 3+ The corresponding preset processing threshold is 0.003wt%.

[0044] Optionally, Pb 2+ The corresponding preset processing threshold is 0.003wt%.

[0045] Optionally, SO4 2- The corresponding preset processing threshold is selected from 0.015 wt %.

[0046] Optionally, CO3 2- The corresponding preset processing threshold is selected from 0.01 wt %.

[0047] Optionally, SiO3 2- The corresponding preset processing threshold is selected from 0.01 wt %.

[0048] Optionally, BO3 3-The corresponding preset processing threshold is selected from 0.01 wt %.

[0049] Optionally, PO4 3- The corresponding preset processing threshold is selected from 0.01 wt %.

[0050] Optionally, the multi-stage filtration is a two-stage filtration, wherein the temperature of the first-stage filtration is 400°C to 700°C, the pore size of the filter mesh is 30μm to 100μm, and the temperature of the second-stage filtration is 400°C to 700°C, the pore size of the filter mesh is 1μm to 30μm.

[0051] Optionally, the temperature of the first-stage filtration is 440°C to 460°C, the pore size of the filter mesh is 30μm to 50μm, and the temperature of the second-stage filtration is 440°C to 460°C, the pore size of the filter mesh is 5μm to 15μm.

[0052] Optionally, multi-stage filtration is performed using a high-temperature molten salt filtration system, which includes a first filtration device and a second filtration device, the first filtration device at least including a molten salt feeding pipe, a first material receiving container and a first filtration mechanism, the first filtration mechanism being arranged between the molten salt feeding pipe and the first material receiving container, so that the molten salt in the molten salt feeding pipe enters the first material receiving container after being filtered by the first filtration mechanism, the second filtration device includes a molten salt conveying pipe connected to the first material receiving container, a second material receiving container and a second filtration mechanism, the second filtration mechanism being arranged between the molten salt conveying pipe and the second material receiving container, so that the molten salt in the first material receiving container enters the second material receiving container after being filtered by the second filtration mechanism.

[0053] Optionally, the first filter mechanism and the second filter mechanism both include a cylinder, a filter screen, a wire brush in contact with the filter screen, a rotating support shaft and arc-shaped fan blades. One end of the cylinder is connected to a pipe at the top, and the other end of the cylinder is provided with a filter screen and is connected to a first material receiving container or a second material receiving container at the bottom. The rotating support shaft is coaxially installed inside the cylinder and the axis of the rotating support shaft is perpendicular to the mesh surface of the filter screen. The wire brush and the arc-shaped fan blades are fixedly connected to the axial direction of the rotating support shaft, and the arc-shaped fan blades are fixedly connected to one end of the rotating support shaft relatively away from the filter screen.

[0054] Optionally, the first filtering device also includes a first sealed storage tank and a first pressurizing component. The molten salt feed pipe is connected to the first sealed storage tank. The bottom of the first sealed storage tank is connected to the first material receiving container through a pipe. The first filtering mechanism is arranged at the connection between the first material receiving container and the feed pipe. The first pressurizing component includes a first pressurizing pipe, a first pressurizing pump and a first pressure gauge. One end of the first pressurizing pipe is connected to the first sealed storage tank, and the other end is connected to the first pressurizing pump. The first pressurizing pipe is provided with a first pressure gauge.

[0055] Optionally, the second filtering device also includes a second sealed storage tank and a second pressurizing component, the molten salt delivery pipeline is connected to the second sealed storage tank, the bottom of the second sealed storage tank is connected to the second material receiving container through a pipeline, the second filtering mechanism is arranged at the connection between the second material receiving container and the feed pipeline, the second pressurizing component includes a second pressurizing pipeline, a second pressurizing pump and a second pressure gauge, one end of the second pressurizing pipeline is connected to the second sealed storage tank, and the other end is connected to the second pressurizing pump, and a second pressure gauge is arranged on the second pressurizing pipeline.

[0056] Optionally, the molten salt feed pipe and / or the molten salt transport pipe is provided with a heating device.

[0057] Optionally, both the first filtering device and the second filtering device are provided with a material inlet and outlet control device.

[0058] Optionally, the curing agent is a sulfate or a phosphate, the sulfate is selected from one or more of potassium sulfate, lithium sulfate, and sodium sulfate, and the phosphate is sodium phosphate.

[0059] Optionally, the ratio of the molar amount of the added curing agent to the total molar amount of the high-potential ions is (0.9-1.4):1, preferably (1-1.2):1.

[0060] Optionally, the ratio of the molar amount of the added curing agent to the total molar amount of the high-potential ions is greater than 1.4:1, and the KCl-LiCl electrolyte is subjected to constant-voltage electrolysis after curing and separation.

[0061] Optionally, when adding the curing agent, the temperature of the electrolyte is controlled to be 400°C to 500°C. After adding the curing agent, the temperature is maintained at 400°C to 1000°C, and the reaction is kept warm for 3 to 5 hours. Preferably, after adding the curing agent, the temperature is maintained at 400°C to 500°C.

[0062] Optionally, after the heat preservation reaction, the temperature is controlled to 400° C. to 500° C. for sedimentation.

[0063] Optionally, the voltage of constant voltage electrolysis is 1V to 3V, preferably 2V to 3V.

[0064] And / or, the temperature of constant voltage electrolysis is 420°C to 480°C, preferably 420°C to 430°C.

[0065] Optionally, before the KCl-LiCl electrolyte raw material is introduced into the metal lithium electrolytic cell, SO4 in the KCl-LiCl electrolyte raw material is detected. 2- 、CO3 2- 、SiO3 2- or BO3 3- Whether at least one reaches the corresponding preset processing threshold or not, if so, it is passed into the pre-electrolysis tank for pre-electrolysis.

[0066] Optionally, the voltage of the pre-electrolysis is 1V to 3V, preferably 2V to 3V.

[0067] Optionally, the temperature of the pre-electrolysis is 420°C to 480°C, preferably 420°C to 430°C.

[0068] Alternatively, SO4 in the KCl-LiCl electrolyte raw material 2- The preset treatment threshold is selected from 0.01 wt % to 0.02 wt %, preferably 0.015 wt %.

[0069] Alternatively, CO3 in the KCl-LiCl electrolyte raw material 2- The preset treatment threshold is selected from 0.008wt% to 0.012wt%, preferably 0.01wt%;

[0070] Alternatively, SiO3 in the KCl-LiCl electrolyte raw material 2- The preset treatment threshold is selected from 0.008 wt % to 0.012 wt %, preferably 0.01 wt %.

[0071] Alternatively, BO3 in the KCl-LiCl electrolyte raw material 3- The preset treatment threshold is selected from 0.008 wt % to 0.012 wt %, preferably 0.01 wt %.

[0072] Optionally, before step S3, it is detected and analyzed whether the electrolyte from which impurities are removed satisfies the following conditions at the same time:

[0073] (1) The content of infusible matter is less than the preset infusible matter processing threshold;

[0074] (2) the contents of various impurities in the high-potential ions are all less than the corresponding preset processing thresholds;

[0075] (3) the contents of various impurities in the low-potential ions are all less than the corresponding preset processing thresholds;

[0076] If the condition is met, proceed to step S3; if not, loop through step S2.

[0077] In the second aspect, the present invention also provides a circulating purification system for KCl-LiCl electrolyte, which includes a high-temperature molten salt filtration system, a solidification reaction vessel, an electrochemical purification system and a metal lithium electrolytic cell. The high-temperature molten salt filtration system, the solidification reaction vessel, the electrochemical purification system and the metal lithium electrolytic cell are connected in series in sequence, and the discharge port of the high-temperature molten salt filtration system, the discharge port of the solidification reaction vessel and the discharge port of the electrochemical purification system are respectively connected to the feed port pipeline of the metal lithium electrolytic cell, and the feed port of the high-temperature molten salt filtration system, the feed port of the solidification reaction vessel and the feed port of the electrochemical purification system are respectively connected to the discharge port of the metal lithium electrolytic cell.

[0078] Optionally, the circulation purification system further comprises a raw material inlet pipe, and the electrochemical purification system and the metal lithium electrolytic cell are both connected to the raw material inlet pipe.

[0079] The present invention has the following beneficial effects: by monitoring the impurities in the electrolyte during the electrolytic preparation of metallic lithium, and according to the monitored impurities, intermittently performing impurity removal operations during the electrolytic production process, the impurities such as infusible solid particles, barium, calcium, magnesium, iron, aluminum, nickel, chromium, lead, etc., which are continuously generated or enriched during the electrolytic preparation of metallic lithium, are effectively removed, and an impurity outlet is continuously provided for the KCl-LiCl electrolyte system. The circulating purification method of the KCl-LiCl electrolyte can maintain high production efficiency and low cost, and the method is particularly suitable for application in a large-scale production environment, and can significantly improve the purity of metallic lithium, improve current efficiency, and extend the life of the electrolytic cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0081] Figure 1 It is a processing flow chart of the circulation purification method according to an embodiment of the present invention;

[0082] Figure 2 It is a structural schematic diagram of a high-temperature molten salt filtration system according to an embodiment of the present invention;

[0083] Figure 3 It is a structural schematic diagram of the first filtering mechanism of the present invention;

[0084] Figure 4 It is a schematic diagram of a circulation purification system according to an embodiment of the present invention.

[0085] Icons: 1-high temperature molten salt filtration system; 10-first filtering device; 11-molten salt feeding pipe; 111-first control valve; 12-first material receiving container; 13-first filtering mechanism; 131-cylinder; 132-filter screen; 133-wire brush; 134-rotating support shaft; 135-arc-shaped fan blade; 136-waste conveying pipe; 137-waste receiving container; 138-fifth control valve; 14-first sealed storage tank; 141-second control valve; 15-first pressurizing assembly; 151-first pressurizing pump, 152-first pressurizing pipeline; 153-first pressure gauge; 20-second filtering device; 21-molten salt delivery pipeline; 211-third control valve; 22-second material receiving container; 23-second filtering mechanism; 24-second sealed storage tank; 241-fourth control valve; 25-second pressurizing assembly; 251-second pressurizing pump, 252-second pressurizing pipeline; 253-second pressure gauge; 2-curing reaction vessel; 3-electrochemical purification system; 31-purification electrolytic cell; 32-filtration kettle; 4-metal lithium electrolytic cell. DETAILED DESCRIPTION

[0086] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0087] The following is a detailed description of a KCl-LiCl electrolyte circulation purification method and system disclosed in the present invention.

[0088] Some embodiments of the present invention provide a method for purifying a KCl-LiCl electrolyte cycle, see Figure 1 , which includes:

[0089] S1. In the process of preparing metallic lithium by electrolysis, the contents of infusible materials, high potential ions and low potential ions of the KCl-LiCl electrolyte in the metallic lithium electrolytic cell are monitored, and it is determined whether the content of the infusible materials reaches or exceeds a preset infusible material processing threshold, whether the content of one or more of the high potential ions reaches or exceeds a corresponding preset processing threshold, and whether the content of one or more of the low potential ions reaches or exceeds a corresponding preset processing threshold;

[0090] S2. Remove impurities according to the monitoring results in the order of priority: infusible materials, high potential ions, and low potential ions:

[0091] If the content of infusibles reaches or exceeds the preset infusible treatment threshold, the electrolyte in the metal lithium electrolytic cell is first subjected to multi-stage filtration to remove the infusibles;

[0092] If the content of one or two of the high-potential ions reaches or exceeds the corresponding preset processing threshold, a curing agent is added to the electrolyte for multi-stage filtration to remove infusibles or the electrolyte for which the monitoring result shows that the infusibles are less than the preset infusible processing threshold, so as to remove the high-potential ions;

[0093] If the content of one or more of the remaining cationic impurities reaches or exceeds the corresponding preset processing threshold, an electrolyte for removing infusibles and / or high-potential ions or an electrolyte whose detection results show that the infusibles and high-potential ions are respectively less than the preset infusible processing threshold and the preset processing threshold corresponding to the high-potential ions is introduced into the pre-electrolysis tank for constant-voltage electrolysis to remove low-potential ions;

[0094] S3. After removing impurities, the electrolyte is filtered and transferred to a metal lithium electrolytic cell for continued use.

[0095] It should be noted that the high potential ions in the above embodiments refer to impurity ions whose decomposition voltage is greater than that of lithium ions, while the low potential ions refer to impurity ions whose decomposition voltage is lower than that of lithium ions. For reference, the high potential ions include Ba 2+ and / or Ca 2+ , low potential ions include SO4 2- 、CO3 2- 、SiO3 2- , BO3 3- PO4 3- Mg 2+ , Fe 2+ 、Al 3+ 、Ni 2+ Cr 3+ and Pb 2+ At least one of .

[0096] In some embodiments, the high potential ions include Ba 2+ and Ca 2+ , low potential ions include at least Mg 2+ , Fe 2+ 、Al 3 + 、Ni 2+ Cr 3+ and Pb 2+ ; Exemplarily, the high potential ions include Ba 2+ and Ca 2+ , the low potential ions include SO4 2- 、CO3 2- 、SiO3 2- , BO3 3- PO4 3- Mg 2+ , Fe 2+ 、Al3+ 、Ni 2+ Cr 3+ and Pb 2+ .

[0097] For reference, the monitoring in the embodiment of the present invention is online monitoring, and its main operation is to regularly or irregularly sample and analyze the electrolyte impurity content during the electrolytic production of metallic lithium. It is understandable that if the technical maturity reaches the point where the impurity content in the electrolytic cell can be directly detected by the sensor, the sensor can be installed in the electrolytic cell to achieve the purpose of monitoring through data transmission.

[0098] It should be noted that the removal of impurities in step S2 will determine certain processing steps and processing sequences according to different impurity monitoring results. Specifically, there are usually the following situations:

[0099] 1. The infusible content in the electrolyte reaches above the preset infusible processing threshold, the content of high-potential ions is less than the corresponding preset processing threshold, and the content of various impurities in the low-potential impurities is less than the corresponding preset processing threshold. The processing process of step S2 in this case is: multi-stage filtration of the electrolyte in the metal lithium electrolytic cell, re-detection of the electrolyte content is less than the preset infusible processing threshold, and then passing it into the metal lithium electrolytic cell for continued electrolysis.

[0100] 2. The content of infusible matter in the electrolyte is less than the preset infusible matter processing threshold, the content of one or more of the high-potential ions reaches or exceeds the preset processing threshold corresponding to the impurities in the high-potential ions, and the content of various impurities in the low-potential ions is less than the corresponding preset processing threshold. The processing process of step S2 in this case is: transfer the electrolyte in the metal lithium electrolytic cell to other containers, add a curing agent to react, filter and re-test the high-potential ion content of the electrolyte to be less than the corresponding preset processing threshold, and then transfer it to the metal lithium electrolytic cell for continued electrolysis.

[0101] 3. The content of infusible materials in the electrolyte is less than the preset infusible material processing threshold, the content of various impurities of high-potential ions is less than the corresponding preset processing threshold, and the content of one or more of the low-potential ions reaches or exceeds the corresponding preset processing threshold. The processing process of step S2 in this case is: transfer the electrolyte in the metal lithium electrolytic cell to the pre-electrolytic cell for constant voltage electrolysis to remove low-potential ions. The contents of various impurities in the remaining cationic impurities in the electrolyte to be re-tested are all less than the corresponding preset processing threshold, and then transferred to the metal lithium electrolytic cell for continued electrolysis.

[0102] 4. The content of infusible materials in the electrolyte is less than the preset infusible material processing threshold, the content of one or more impurities in the high-potential ions reaches above the corresponding preset processing threshold, and the content of one or more low-potential ions reaches above the corresponding preset processing threshold. The processing process of step S2 in this case is: transfer the electrolyte in the metal lithium electrolytic cell to other containers, add a curing agent to react, filter and then transfer to the pre-electrolytic cell for constant voltage electrolysis, and then filter again, re-detect the high-potential ions in the electrolyte to be less than the corresponding preset processing threshold and the content of various impurities in the low-potential ions are less than the corresponding preset processing threshold, and then transfer to the metal lithium electrolytic cell to continue electrolysis.

[0103] 5. The content of infusible matter in the electrolyte reaches above the preset infusible matter processing threshold, the content of one or more impurities in the high-potential ions reaches above the corresponding preset processing threshold, and the content of various impurities in the low-potential ions is less than the corresponding preset processing threshold. The processing process of step S2 in this case is: multi-stage filtration of the electrolyte in the metal lithium electrolytic cell, and then transfer it to other containers, add a curing agent to react, and re-test the electrolyte after filtering. After the content of infusible matter is less than the preset infusible matter processing threshold and the content of high-potential ions is less than the corresponding preset processing threshold, it is transferred to the metal lithium electrolytic cell for continued electrolysis.

[0104] 6. The content of infusible materials in the electrolyte reaches above the preset infusible material processing threshold, the content of high-potential ions is less than the corresponding preset processing threshold, and the content of one or more low-potential ions reaches above the corresponding preset processing threshold. The processing process of step S2 in this case is: the electrolyte in the metal lithium electrolytic cell is subjected to multi-stage filtration, and then transferred to the pre-electrolytic cell for constant voltage electrolysis to remove low-potential ions, and after filtering again to detect that the impurities in the electrolyte are lower than the processing threshold, it is transferred to the metal lithium electrolytic cell for continued electrolysis.

[0105] 7. The content of infusibles in the electrolyte reaches above the preset infusible processing threshold, the content of one or more impurities in the high-potential ions reaches above the corresponding preset processing threshold, and the content of one or more impurities in the low-potential ions reaches above the corresponding preset processing threshold. The processing process of step S2 in this case is: the electrolyte in the metal lithium electrolytic cell is subjected to multi-stage filtration, and then transferred to other containers to add a curing agent for reaction. After filtration, the pre-electrolytic cell is transferred for constant voltage electrolysis to remove low-potential ions. After filtering again and detecting that the impurities in the electrolyte are lower than the processing threshold, it is transferred to the metal lithium electrolytic cell for continued electrolysis.

[0106] The above embodiments of the present invention remove different types of impurities in strict accordance with the following priority order to achieve a better treatment effect. First, the infusible matter exists in the electrolyte as a foreign matter, which may act as a reaction barrier, hindering the effective contact and reaction between the high-potential ions and the curing agent, and may also have other side reactions with the curing agent, thereby significantly reducing the rate and efficiency of the curing reaction. Secondly, the infusible matter in the electrolyte will occupy the space originally used for ion conduction, increase the resistivity of the electrolyte, and cause the conductivity of the molten salt to be significantly reduced. This not only affects the overall impurity removal efficiency of the electrochemical process, but also may increase energy consumption; at the same time, the deposition or adsorption of the infusible matter on the cathode surface will form a thin film that hinders electron transfer, that is, the cathode passivation phenomenon. This not only reduces the activity of the cathode, but may also cause the current efficiency to decrease during the electrochemical impurity removal process, further affecting the impurity removal efficiency. The reasons why high-potential ions need to be removed before electrochemical impurity removal are: (1) In the KCl-LiCl electrolyte, the decomposition voltage (absolute value) of high-potential ions is higher than the decomposition voltage (absolute value) of lithium ions and low-potential ions. Therefore, when constant voltage (decomposition voltage of high-potential ions) is used for impurity removal, lithium ions will also be electrolyzed out, so electrochemical impurity removal is not used to remove barium ions and calcium ions; (2) The added curing agent may remain, and since the decomposition voltage (absolute value) of the curing agent is lower than the decomposition voltage (absolute value) of lithium ions, it can be removed by electrochemical methods.

[0107] In some embodiments, since the generation or enrichment of impurities in the process of producing lithium by electrolysis requires a period of electrolysis before one or more of the infusible substances, high potential ions, and low potential ions correspond to the preset processing threshold, in order to save manpower and material resources, the infusible substances, Ba in the electrolyte of the metal lithium electrolytic cell are monitored. 2+ , Ca 2+ The frequency of the content of the remaining cationic impurities is 5 to 20 days / time. For example, according to the speed of impurity generation or enrichment, the frequency can be selected from 5 days / time, 6 days / time, 7 days / time, 8 days / time, 9 days / time, 10 days / time, 11 days / time, 12 days / time, 13 days / time, 14 days / time, 15 days / time, 16 days / time, 17 days / time, 18 days / time, 19 days / time or 20 days / time. Generally speaking, in the early stage of electrolytic cell operation, the monitoring frequency can be longer, and the detection interval can be gradually shortened in the later stage.

[0108] In order to achieve better control purposes, that is, based on the impact of impurity content on product purity and the electrolytic cell, in some embodiments, the preset infusible material processing threshold is selected from 0.04wt% to 0.06wt%, for example, it can be set to 0.04wt%, 0.045wt%, 0.05wt%, 0.055wt%, 0.06wt%, etc.

[0109] In some embodiments, Ba2+ The corresponding preset processing threshold is selected from 0.25wt% to 0.35wt%, for example, it can be set to 0.025wt%, 0.026wt%, 0.027wt%, 0.028wt%, 0.029wt%, 0.03wt%, 0.031wt%, 0.032wt%, 0.033wt%, 0.034wt% or 0.035wt%, etc. Ca 2+ The corresponding preset processing threshold is selected from 0.1wt% to 0.14wt%, such as 0.1wt%, 0.11wt%, 0.12wt%, 0.13wt% or 0.14wt%.

[0110] In some embodiments, Mg 2+ The corresponding preset processing threshold is selected from 0.02wt% to 0.04wt%, such as 0.02wt%, 0.025wt%, 0.03wt%, 0.035wt% or 0.04wt%. 2+ The corresponding preset processing threshold is selected from 0.008wt% to 0.012wt%, such as 0.008wt%, 0.009wt%, 0.01wt%, 0.011wt% or 0.012wt%. 3+ The corresponding preset processing threshold is selected from 0.008wt% to 0.012wt%, 0.008wt%, 0.009wt%, 0.01wt%, 0.011wt% or 0.012wt%, etc. Ni 2+ The corresponding preset processing threshold is selected from 0.002wt% to 0.004wt%, such as 0.02wt%, 0.025wt%, 0.03wt%, 0.035wt% or 0.04wt%. 3+ The corresponding preset processing threshold is selected from 0.002wt% to 0.004wt%, such as 0.02wt%, 0.025wt%, 0.03wt%, 0.035wt% or 0.04wt%. 2+ The corresponding preset processing threshold is selected from 0.002wt% to 0.004wt%, such as 0.02wt%, 0.025wt%, 0.03wt%, 0.035wt% or 0.04wt%. SO4 2- The corresponding preset processing threshold is selected from 0.01wt% to 0.02wt%, such as 0.01wt%, 0.011wt%, 0.012wt%, 0.013wt%, 0.014wt%, 0.015wt%, 0.016wt%, 0.017wt%, 0.018wt%, 0.019wt% or 0.02wt%, etc., preferably 0.015wt%. CO3 2-The corresponding preset treatment threshold is selected from 0.008wt% to 0.012wt%, such as 0.008wt%, 0.009wt%, 0.01wt%, 0.011wt% or 0.012wt%, etc., preferably 0.01wt%. SO3 2- The corresponding preset processing threshold is selected from 0.008wt% to 0.012wt%, such as 0.008wt%, 0.009wt%, 0.01wt%, 0.011wt% or 0.012wt%, etc., preferably 0.01wt%. PO4 3- The corresponding preset processing threshold is selected from 0.008wt% to 0.012wt%, such as 0.008wt%, 0.009wt%, 0.01wt%, 0.011wt% or 0.012wt%, etc., preferably 0.01wt%. BO3 3- The corresponding preset processing threshold is selected from 0.008wt% to 0.012wt%, such as 0.008wt%, 0.009wt%, 0.01wt%, 0.011wt% or 0.012wt%, etc., preferably 0.01wt%.

[0111] Furthermore, in some preferred embodiments, the preset infusible material processing threshold is 0.05wt%; Ba 2+ The corresponding preset treatment threshold is 0.3wt%; Ca 2+ The corresponding preset treatment threshold is 0.1wt%; Mg 2+ The corresponding preset treatment threshold is 0.03wt%; Fe 2+ The corresponding preset processing threshold is 0.01wt%; Al 3+ The corresponding preset treatment threshold is 0.01wt%; Ni 2+ The corresponding preset processing threshold is 0.003wt%; Cr 3+ The corresponding preset treatment threshold is 0.003wt%; Pb 2+ The corresponding preset processing threshold is 0.003wt%.

[0112] The infusible impurities produced during the electrolysis of KCl-LiCl electrolyte include some infusible impurities existing in the raw materials, as well as some corrosion products of electrode materials and detached materials of the electrolytic cell lining, etc., and their composition is relatively complex and the particle size distribution is relatively large. Therefore, if a single filtration is performed, it is easy to cause the filter holes to be blocked, and it cannot achieve a better filtering operation and effect. Therefore, in order to meet the needs, generally speaking, multi-stage filtration is a two-stage filtration, in which the temperature of the first stage filtration is 400℃~700℃. Exemplarily, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃ or 700℃ can be selected. Usually, it is sufficient to fully melt the KCl-LiCl electrolyte. The pore size of the filter mesh is 30μm~100μm. Exemplarily, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm or 100μm, etc., or between any two of the above apertures, the temperature of the secondary filtration is 400℃~700℃, illustratively, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃ or 700℃, etc. can be selected, and the filter mesh is 1μm~30μm, illustratively, 1μm, 5μm, 10μm, 15μm, 20μm, 25μm or 30μm, etc., or between any two of the above apertures. It can be understood that in other embodiments, more levels of filtration can also be set as needed, but the process flow and cost of the treatment will be significantly increased.

[0113] Further according to actual conditions and taking into account costs, etc., in some implementations, the temperature of the first-stage filtration is 440°C to 460°C, the pore size of the filter mesh is 30μm to 50μm, and the temperature of the second-stage filtration is 440°C to 460°C, and the pore size of the filter mesh is 5μm to 15μm.

[0114] See again Figure 1 In some embodiments, before the KCl-LiCl electrolyte raw material is introduced into the metal lithium electrolytic cell, SO4 in the KCl-LiCl electrolyte raw material is detected. 2- 、CO3 2- 、SiO3 2- or BO3 3- Whether at least one reaches the corresponding preset processing threshold or not, if so, it is passed into the pre-electrolysis tank for pre-electrolysis.

[0115] In some embodiments, the voltage of the pre-electrolysis is 1 V to 3 V, such as 1.1 V, 1.2 V, 1.3 V, 1.4 V, 1.5 V, 1.6 V, 1.7 V, 1.8 V, 1.9 V, 2.0 V, 2.1 V, 2.2 V, 2.3 V, 2.4 V, 2.5 V, 2.6 V, 2.7 V, 2.8 V, 2.9 V and 3.0 V, etc., preferably 2 V to 3 V. The temperature of the pre-electrolysis is 420° C. to 480° C., such as 420° C., 430° C., 440° C., 450° C., 460° C., 470° C. or 480° C., etc., preferably 420° C. to 430° C.

[0116] As a reference, SO4 in KCl-LiCl electrolyte raw materials 2- The preset processing threshold is selected from 0.01wt% to 0.02wt%, such as 0.01wt%, 0.011wt%, 0.012wt%, 0.013wt%, 0.014wt%, 0.015wt%, 0.016wt%, 0.017wt%, 0.018wt%, 0.019wt% or 0.02wt%, etc., preferably 0.015wt%. CO3 in KCl-LiCl electrolyte raw materials 2- The preset treatment threshold is selected from 0.008wt% to 0.012wt%, such as 0.008wt%, 0.009wt%, 0.01wt%, 0.011wt% or 0.012wt%, etc., preferably 0.01wt%. SiO3 in KCl-LiCl electrolyte raw materials 2- The preset processing threshold is selected from 0.008wt% to 0.012wt%, such as 0.008wt%, 0.009wt%, 0.01wt%, 0.011wt% or 0.012wt%, etc., preferably 0.01wt%. 3- The preset processing threshold is selected from 0.008wt% to 0.012wt%, such as 0.008wt%, 0.009wt%, 0.01wt%, 0.011wt% or 0.012wt%, etc., preferably 0.01wt%.

[0117] join Figure 2The multi-stage filtration adopts a high-temperature molten salt filtration system 1 for filtration. The high-temperature molten salt filtration system 1 includes a first filtration device 10 and a second filtration device 20. The first filtration device at least includes a molten salt feed pipe 11, a first material receiving container 12 and a first filtration mechanism 13. The first filtration mechanism 13 is arranged between the molten salt feed pipe 11 and the first material receiving container 12, so that the molten salt in the molten salt feed pipe 11 enters the first material receiving container 12 after being filtered by the first filtration mechanism 13. The second filtration device 20 includes a molten salt delivery pipeline 21 connected to the first material receiving container 12, a second material receiving container 22 and a second filtration mechanism 23. The second filtration mechanism 23 is arranged between the molten salt delivery pipeline 21 and the second material receiving container 22, so that the molten salt in the first material receiving container 12 enters the second material receiving container 22 after being filtered by the second filtration mechanism 23. Among them, the aperture of the filter mesh of the first filtration mechanism 13 is larger than the aperture of the filter mesh of the second filtration mechanism 23. It should be noted that, generally speaking, the first filter device 10 is disposed above the second filter device 20 to facilitate the transportation of the molten salt by gravity. Of course, in other embodiments, they can also be placed side by side and transported by a power delivery device such as a pressure pump.

[0118] Further, the first filtering device 10 also includes a first sealed storage tank 14 and a first pressurizing assembly 15, the molten salt feed pipe 11 is connected to the first sealed storage tank 14, that is, the molten salt enters the first sealed storage tank 14 through the molten salt feed pipe 11 for storage, the bottom of the first sealed storage tank 14 is connected to the first receiving container 12 through a pipeline, and the first filtering mechanism 13 is arranged at the connection between the first receiving container 12 and the feed pipeline, that is, the molten salt in the first sealed storage tank 14 can be filtered by the first filtering mechanism 13 and then enter the first receiving container 12. However, since the density of the molten salt is large and the particles of the infusible material contain larger particles, therefore, if it is transported only under gravity, the molten salt is not easy to pass through the filter mesh, and the filter mesh is also more likely to cause blockage. Therefore, the first pressurizing assembly 15 is provided to provide power for the filtration of the molten salt and reduce the risk of blockage.

[0119] Specifically, the first pressurizing assembly 15 includes a first pressurizing pump 151, a first pressurizing pipe 152, and a first pressure gauge 153. One end of the first pressurizing pipe 152 is connected to the first sealed material storage tank 14, and the other end is connected to the first pressurizing pump 151. The first pressurizing pipe 152 is provided with a first pressure gauge 153. The first pressurizing pump 151 can pump air to the first pressurizing pipe 152, and then enter the first sealed material storage tank 14, and form a certain pressure in the first sealed material storage tank 14. The first pressure gauge 153 can be used to observe whether the pressure in the first sealed material storage tank 14 reaches the preset pressure.

[0120] Further, the second filtering device 20 also includes a second sealed storage tank 24 and a second pressurizing assembly 25, the molten salt delivery pipeline 21 is connected to the second sealed storage tank 24, that is, the molten salt enters the second sealed storage tank 24 through the molten salt delivery pipeline 21 for storage, the bottom of the second sealed storage tank 24 is connected to the second receiving container 22 through a pipeline, and the second filtering mechanism 23 is arranged at the connection between the second receiving container 22 and the feed pipeline, that is, the molten salt in the second sealed storage tank 24 can be filtered by the second filtering mechanism 23 and then enter the second receiving container 22. The second pressurizing assembly 25 is provided to provide power for the filtration of the molten salt and reduce the risk of blockage.

[0121] Specifically, the second pressurizing assembly 25 includes a second pressurizing pump 251, a second pressurizing pipe 252, and a second pressure gauge 253. One end of the second pressurizing pipe 252 is connected to the second sealed material storage tank 24, and the other end is connected to the second pressurizing pump 251. The second pressurizing pipe 252 is provided with a second pressure gauge 253. The second pressurizing pump 251 can pump air to the second pressurizing pipe 252, and then enter the second sealed material storage tank 24, and form a certain pressure in the second sealed material storage tank 24. The second pressure gauge 253 can be used to observe whether the pressure in the second sealed material storage tank 24 reaches the preset pressure.

[0122] It should be noted that the second filter device 20 may consider whether to set the second sealed storage tank 24 and the second pressurizing component 25 according to actual conditions. That is, in some embodiments, when the secondary filtration will not be blocked, the second filter device 20 may not set the second sealed storage tank 24 and the second pressurizing component 25, and directly connect the first material receiving container 12 and the second material receiving container 22 through the molten salt delivery pipeline 21, and the second material receiving container 22 may be set below the first material receiving container 12, or a material delivery pump may be set in the molten salt delivery pipeline 21 to provide power.

[0123] Furthermore, in some embodiments, the molten salt feed pipe 11 and / or the molten salt delivery pipe 21 are provided with a heating device. For example, a heating component is provided on the surface of the pipe to heat the molten salt in the pipe. The setting of the heating component can keep the molten salt in a molten state at a certain temperature and have better fluidity. At the same time, the molten salt can also maintain a certain temperature during the subsequent filtration process.

[0124] Further, the first filter device 10 and the second filter device 20 are both provided with a feed and discharge control device. Specifically, a first control valve 111 may be provided on the molten salt feed pipe 11, and a second control valve 141 may be provided on the pipeline between the first sealed material storage tank 14 and the first material receiving container 12. A third control valve 211 may be provided on the molten salt delivery pipeline 21, and a fourth control valve 241 may be provided on the pipeline between the second sealed material storage tank 24 and the second material receiving container 22. The above control valve settings enable the filtration system to achieve flexible control of molten salt delivery.

[0125] Furthermore, participate Figure 3 The first filter mechanism 13 and the second filter mechanism 23 each include a cylinder 131, a filter screen 132, a wire brush 133 in contact with the filter screen, a rotating support shaft 134, and an arc-shaped fan blade 135. One end of the cylinder 131 is connected to the upper pipe, and the other end of the cylinder 131 is provided with the filter screen 132, and is connected to the first material receiving container 12 or the second material receiving container 22 at the lower part. The rotating support shaft 134 is coaxially installed inside the cylinder 131, and the axis of the rotating support shaft 134 is perpendicular to the mesh surface of the filter screen 132 (it should be noted that the perpendicular here is substantially perpendicular). The wire brush 133 and the arc-shaped fan blade 135 are both fixedly connected to the axial direction of the rotating support shaft 134, and the arc-shaped fan blade 135 is fixedly connected to one end of the rotating support shaft 134 that is relatively far away from the filter screen 132. Specifically, the upper part of the cylinder 131 is a small diameter part, which can be connected to the pipeline by welding or integral molding, and the lower part is a large diameter part, the end of which is closed with a filter screen, that is, a larger filter cavity is formed inside the large diameter part. The arc-shaped fan blade 135 is located in the small diameter part of the cylinder 131, and the outer diameter formed by the arc-shaped fan blade 135 is slightly smaller than the small diameter part of the cylinder 131, so that the molten salt can reach the bottom through the inner and peripheral flow channels of the arc-shaped fan blade 135. It should be noted that the arc-shaped fan blade 135 has multiple groups of blades, and the arc-shaped fan blade 135 can rotate under the weight of the molten salt flowing down from the top. The wire brush 133 is located at the bottom of the rotating support shaft 134 and contacts the filter screen 132, that is, under the action of the rotating force of the arc-shaped fan blade 135, the rotating support shaft 134 rotates, thereby driving the wire brush 133 to clean the filter screen 132 to avoid reducing the possibility of clogging of the filter screen 132.

[0126] Therefore, the molten salt moves from the upper pipe to the arc-shaped fan blade 135 under the action of gravity, causing the arc-shaped fan blade 135 to rotate, and the molten salt reaches the bottom from the gaps between the blades of the arc-shaped fan blade 135 and the peripheral gaps. The rotation of the arc-shaped fan blade 135 drives the rotating support shaft 134 to rotate, and then drives the wire brush 133 to rotate, thereby cleaning the filter screen. After the molten salt flows through the gaps of the wire brush, it is filtered through the filter screen.

[0127] Further, see Figure 1 and Figure 2 The first filter mechanism 13 and the second filter mechanism 23 both include a waste conveying pipe 136 and a waste receiving container 137 connected to the waste conveying pipe 136. The waste receiving pipe 136 is also provided with a fifth control valve 138. The infusible material deposited in the cavity where the wire brush 133 is located can be continuously sucked out through the waste conveying pipe 136 to achieve a better continuous filtering effect. Among them, a suction pump that provides power for suction can be provided on the waste conveying pipe 136.

[0128] In some embodiments, removal of high potential ions (e.g., Ba 2+ and Ca 2+ ) The curing agent selected is sulfate and phosphate. For example, phosphate includes but is not limited to one or more of potassium sulfate, lithium sulfate, sodium sulfate and sodium phosphate. The curing reactions are:

[0129] BaCl2+K2SO4=BaSO4↓+2KCl;

[0130] BaCl2+Li2SO4=BaSO4↓+2LiCl;

[0131] BaCl2+Na2SO4=BaSO4↓+2NaCl;

[0132] 3BaCl2+2Na3PO4=Ba3(PO4)2↓+6NaCl;

[0133] CaCl2+K2SO4=CaSO4↓+2KCl;

[0134] CaCl2+Li2SO4=CaSO4↓+2LiCl;

[0135] CaCl2+Na2SO4=CaSO4↓+2NaCl;

[0136] 3CaCl2+2Na3PO4=Ca3(PO4)2↓+6NaCl.

[0137] In some embodiments, in order to allow the added sulfate and phosphate to react with high potential ions (such as Ba 2+ and Ca 2+ ) can be fully removed, the sulfate / phosphate ions and Ba in the added sulfate and phosphate 2+ / Ca 2+The molar ratio is (0.9-1.4):1, for example, 0.9:1, 0.95:1, 1:1, 1.05:1, 1.1:1, 1.15:1, 1.2:1, 1.25:1, 1.3:1, 1.35:1 and 1.4:1, etc., preferably (1-1.2):1.

[0138] In some embodiments, the ratio of the molar amount of the added curing agent to the total molar amount of the high-potential ions is greater than 1.4:1, and the KCl-LiCl electrolyte is subjected to constant-voltage electrolysis after curing and separation to remove excess sulfate ions remaining from the curing reaction.

[0139] In order to allow sulfate / phosphate ions to fully react with high potential ions (such as Ba 2+ and Ca 2+ ) for precipitation, and achieve a better reaction effect. In some embodiments of the present invention, the reaction treatment effect is improved by heating the reaction. That is, when adding the curing agent, the temperature of the electrolyte is controlled to be 400°C to 500°C, such as 400°C, 420°C, 430°C, 440°C, 450°C, 460°C, 480°C or 500°C, etc. After adding the curing agent, the temperature is raised to 400°C to 1000°C, such as 400°C, 500°C, 600°C, 700°C, 800°C, 900°C or 1000°C, etc., and the temperature is kept for 1 to 5 hours, such as 1 hour, 2 hours, 3 hours, 4 hours or 5 hours, etc.

[0140] In some embodiments, when the curing reaction temperature is higher than 500°C, the above-mentioned precipitated high potential ions (such as Ba 2+ and Ca 2+ ) is kept warm for reaction, the temperature is lowered to 400° C. to 500° C. for sedimentation, and then the precipitate is removed by filtration. The filtration method includes but is not limited to natural filtration, vacuum filtration, etc.

[0141] Further, in the operation of removing low-potential ions, a suitable voltage can promote the low-potential ions to undergo a specific redox reaction at the electrode, thereby effectively removing them. If the voltage is too low, the redox of impurities may be difficult to carry out, and the removal efficiency may be low; if the voltage is too high, side reactions may be triggered, producing other impurities or causing transition corrosion to the electrode. The inventors of the present application have conducted a lot of research and practice on the specific types of low-potential ions in the KCl-LiCl electrolyte. In some embodiments, the voltage of constant-potential electrolysis is selected to be 1V to 3V, such as 1.0V, 1.1V, 1.2V, 1.3V, 1.4V, 1.5V, 1.6V, 1.7V, 1.8V, 1.9V, 2.0V, 2.1V, 2.2V, 2.3V, 2.4V, 2.5V, 2.6V, 2.7V, 2.8V, 2.9V and 3.0V, etc., preferably 2V to 3V.

[0142] In some embodiments, the temperature of constant voltage electrolysis is 420°C to 480°C, for example, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C or 480°C, etc., preferably 420°C to 430°C.

[0143] In some embodiments, before step S3, the electrolyte from which impurities are removed is detected and analyzed to see whether the following conditions are met at the same time: (1) the content of infusibles is less than the preset infusible processing threshold; (2) the content of high-potential ions is less than the corresponding preset processing threshold; (3) the content of various impurities in low-potential ions is less than the corresponding preset processing threshold; if the conditions are met, step S3 is performed; if not, step S2 is performed in a loop. It should be noted that after treating a certain impurity alone, detection and analysis can also be performed, and the operation is repeated if the requirements are not met. For example, after the high-potential ions are removed by the curing reaction, it is detected whether the content of the high-potential ions is less than the corresponding preset processing threshold. If it is less than, other operations are performed. If the content of one or more impurities in the high-potential ions is above the corresponding preset processing threshold, the curing process is performed again.

[0144] For reference, some implementations are based on the following situations:

[0145] Set the processing thresholds for each type of impurity as:

[0146] Impurity Type Treatment threshold (wt%) Infusible 0.05 <![CDATA[Ba 2 ]]> 0.3 <![CDATA[Ca 2 ]]> 0.1 Mg2 0.03 Fe2 0.01 Al3 0.01 <![CDATA[Ni 2+ ]]> 0.003 <![CDATA[Cr 3+ ]]> 0.003 <![CDATA[Pb 2 ]]> 0.003

[0147] (1) The infusible content is above 0.05wt%, and the Ba2, Ca 2+ The contents of the remaining cationic impurities are all lower than the corresponding preset processing thresholds.

[0148] Steps: using a high-temperature molten salt multi-stage filtration system to filter the electrolyte in the electrolytic cell, and transfer it to a stainless steel kettle A; using a high-temperature molten salt multi-stage filtration system to filter the electrolyte in the stainless steel kettle A again, and filter it into a stainless steel filter kettle B; testing the infusible content of the filtered electrolyte, and transferring it to the electrolytic cell for continued use;

[0149] Among them, the preferred primary filtration temperature is 450° C. and the filtration pore size is 30-50 μm; the preferred secondary filtration temperature is 450° C. and the filtration pore size is 5-15 μm.

[0150] (2) The infusible content is less than 0.05wt%, Ba2 and Ca 2+ One or both of them reach the corresponding preset processing threshold, and the contents of the remaining cationic impurities do not reach the corresponding preset processing threshold.

[0151] Steps: transfer the metal lithium electrolyte to the stainless steel kettle C and heat it to maintain it within a certain temperature range, add a curing agent, and stir; after adding the curing agent, heat it up and keep it warm for reaction, and after the reaction is completed, cool it down for sedimentation; after sedimentation is completed, filter the electrolyte and transfer the filtrate to the production electrolytic cell for continued use.

[0152] The temperature of the curing agent is 400-500℃, and the amount added is 90%-110%. The heat preservation temperature is 400-1000℃, the heat preservation reaction time is 1-5h, and the temperature of the cooling sedimentation is 400-500℃, and the sedimentation is clear to the upper layer of the electrolyte. The filtration method is natural filtration and vacuum filtration.

[0153] (3) The infusible content is less than 0.05wt%, Ba2 and Ca 2+ None of them reached the corresponding preset processing threshold, and one or more of the remaining impurity contents reached the corresponding preset processing threshold.

[0154] Steps: transfer the metal lithium electrolyte to the pre-electrolyzer D and keep it within a certain range; perform constant voltage electrolysis, and maintain the voltage at about 1V to 3V; perform sampling and analysis, and after the composition is normal, filter it and transfer the filtrate to the production electrolyzer for continued use.

[0155] The pre-electrolysis temperature is 420°C to 480°C, preferably 420°C to 430°C, the pre-electrolysis voltage is 1V to 3V, preferably 2V to 3V; and the filtration methods include natural filtration and vacuum filtration.

[0156] (4) The infusible content is less than 0.05wt%, Ba2 and Ca 2+ One or more of the remaining impurity contents reach the corresponding preset processing thresholds.

[0157] Steps: transfer the metal lithium electrolyte to the stainless steel kettle C and heat it to maintain the temperature within a certain range, add the curing agent and stir; after adding the curing agent, heat it up and keep it warm for reaction, and after the reaction is completed, cool it down for sedimentation; after sedimentation is completed, filter the electrolyte at high temperature, transfer the filtrate to the pre-electrolyzer D, and maintain it within a certain range; perform constant voltage electrolysis, and maintain the voltage at about 1 to 3V; perform sampling and analysis, and after the composition is normal, filter it, and transfer the filtrate to the production electrolyzer for continued use.

[0158] The temperature of the curing agent is 400-500°C, and the amount added is 90%-110% of the theoretical amount. The heat preservation temperature is 400-1000°C, the heat preservation reaction time is 1-5h, the cooling and sedimentation temperature is 400-500°C, and the sedimentation is clear on the upper layer of the electrolyte. The pre-electrolysis temperature is 420-480°C, preferably 420-430°C, and the pre-electrolysis voltage is 1V-3V, preferably 2V-3V. The filtration methods include natural filtration and vacuum filtration.

[0159] (5) The infusible content is above 0.05wt%, Ba2 and Ca 2+ One or both of the impurities reach the corresponding preset processing threshold, and the contents of the remaining impurities do not reach the corresponding preset processing threshold.

[0160] Steps: Use a high-temperature molten salt multi-stage filtration system to perform primary filtration on the electrolyte in the electrolytic cell and transfer it to a stainless steel kettle A; use the high-temperature molten salt multi-stage filtration system to filter the electrolyte in the stainless steel kettle A again and filter it into a stainless steel filter kettle B; transfer the electrolyte to a stainless steel kettle C and heat it to maintain it within a certain temperature range, add a curing agent and stir it; after adding the curing agent, heat it up and carry out a heat preservation reaction, and after the reaction is completed, cool it down and settle it; after settling is completed, filter the electrolyte and transfer the filtrate to the production electrolytic cell for continued use.

[0161] The primary filtration temperature is 430-480℃, and the filtration aperture is 30-60μm. The secondary filtration temperature is 430-480℃, and the filtration aperture is 30-60μm. The curing agent temperature is 400-500℃, the addition amount is 90%-110% of the theoretical amount, the insulation temperature is 400-1000℃, the insulation reaction time is 1-5h, the cooling and sedimentation temperature is 400-500℃, and the sedimentation is clear to the upper layer of the electrolyte. The filtration method is vacuum filtration or natural filtration.

[0162] (6) The infusible content is above 0.05wt%, Ba2 and Ca 2+ None of them reached the corresponding preset processing threshold, and one or more of the remaining impurity contents reached the corresponding preset processing threshold.

[0163] Steps: Use a high-temperature molten salt multi-stage filtration system to perform primary filtration on the electrolyte in the electrolytic cell and transfer it to a stainless steel kettle A; use a high-temperature molten salt multi-stage filtration system to filter the electrolyte in the stainless steel kettle A again and filter it into a stainless steel filter kettle B; transfer the secondary filtrate to a pre-electrolytic cell D to maintain it within a certain temperature range; perform constant voltage electrolysis with the voltage maintained at about 1V to 3V; perform sampling and analysis, and after the composition is normal, filter it and transfer the filtrate to a production electrolytic cell for continued use.

[0164] Among them, the primary filtration temperature is 400-700°C, and the filtration pore size is 30-100 μm. The secondary filtration temperature is 400-700°C, and the filtration pore size is 1-30 μm, preferably: the filtration temperature is 450°C, and the filtration pore size is 5-15 μm. The pre-electrolysis temperature is 420°C-480°C, preferably 420°C-430°C, and the pre-electrolysis voltage is 1V-3V, preferably 2V-3V. The filtration methods include natural filtration and vacuum filtration.

[0165] (7) The infusible content is above 0.05wt%, Ba2 and / or Ca 2+ The content of reaches the corresponding preset processing threshold, and the content of one or more of the remaining impurities reaches the preset processing threshold.

[0166] Steps: Use a high-temperature molten salt multi-stage filtration system to perform primary filtration on the electrolyte in the electrolytic cell and transfer it to a stainless steel kettle A; use the high-temperature molten salt multi-stage filtration system to filter the electrolyte in the stainless steel kettle A again and filter it into a stainless steel filter kettle B; transfer the secondary filtered electrolyte to a stainless steel kettle C and heat it to maintain it within a certain temperature range, add a curing agent and stir it; after adding the curing agent, heat it up and carry out a heat preservation reaction, and after the reaction is completed, cool it down and settle it; after the sedimentation is completed, filter the electrolyte and transfer the liquid to a pre-electrolytic cell D to maintain it within a certain temperature range; perform constant voltage electrolysis, and maintain the voltage at about 1 to 3V; take samples for analysis, and after the composition is normal, filter it, and transfer the filtrate to the production electrolytic cell for continued use.

[0167] Among them, the primary filtration temperature is 400-700℃, and the filtration pore size is 30-100μm. The secondary filtration temperature is 400-700℃, and the filtration pore size is 1-30μm. The temperature of adding barium ion curing agent is 400-500℃, and the addition amount is 90%-110% of the theoretical amount. The insulation temperature is 400-1000℃, the insulation reaction time is 1-5h, the cooling and sedimentation temperature is 400-500℃, and it is settled to the upper layer of the electrolyte to be clear. The pre-electrolysis temperature is 420℃-480℃, preferably 420℃-430℃, and the pre-electrolysis voltage is 1-3V, preferably 2V-3V. The filtration methods include natural filtration and vacuum filtration.

[0168] Furthermore, participate Figure 4Some embodiments of the present invention also provide a circulating purification system for KCl-LiCl electrolyte, which includes a high-temperature molten salt filtration system 1, a solidification reaction vessel 2, an electrochemical purification system 3 and a metal lithium electrolytic cell 4, wherein the high-temperature molten salt filtration system 1, the solidification reaction vessel 2, the electrochemical purification system 3 and the metal lithium electrolytic cell 4 are sequentially connected in series, and the discharge port of the high-temperature molten salt filtration system 1, the discharge port of the solidification reaction vessel 2 and the discharge port of the electrochemical purification system 3 are all connected to the feed port pipeline of the metal lithium electrolytic cell 4, and the feed port of the high-temperature molten salt filtration system 1, the feed port of the solidification reaction vessel 2 and the feed port of the electrochemical purification system 3 are respectively connected to the discharge port of the metal lithium electrolytic cell 4. In addition, the circulating purification system also includes a raw material inlet pipe, and the electrochemical purification system 3 and the metal lithium electrolytic cell 4 are both connected to the raw material inlet pipe. That is, when the KCl-LiCl electrolyte raw material is detected to be in compliance with the standard, it directly enters the metal lithium electrolytic cell 4 for the electrolysis operation to generate lithium; when the KCl-LiCl electrolyte raw material is detected to contain some impurities exceeding the standard, the raw material is first passed into the electrochemical purification system 3 for pre-electrolysis, and then enters the metal lithium electrolytic cell 4 for the electrolysis operation to generate lithium.

[0169] It should be noted that the electrochemical purification system 3 further includes a purification electrolytic cell 31 and a filter kettle 32, and the purification electrolytic cell 31 is connected to the filter kettle 32 through a pipeline. The purification electrolytic cell 31 serves as an electrolytic cell for constant-pressure electrolysis of the aforementioned electrolyte to remove remaining cationic impurities and a pre-electrolytic cell for pre-electrolysis of the electrolyte raw material.

[0170] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0171] The following examples and comparative examples use the following standards as preset processing thresholds for each impurity.

[0172]

[0173]

[0174] Example 1

[0175] This embodiment provides a circulating purification method for KCl-LiCl electrolyte, using Figure 4 The circulation system shown is processed, which includes:

[0176] (1) Online monitoring: Online monitoring shows that the content of infusible matter in the metal lithium electrolyte is 0.0720wt%, and the Ba in the electrolyte 2 , Ca 2 The contents of other impurities are all below the preset processing threshold.

[0177] (2) Filtering and analysis: Installation Figure 2 and Figure 3The high-temperature molten salt filtration system 1 shown in the figure performs primary filtration (filtration aperture of 50 μm, filtration temperature of 450°C) to allow the abnormal electrolyte to enter the first receiving container 12. Secondary filtration (filtration aperture of 10 μm, filtration temperature of 450°C) is performed again to allow the electrolyte to enter the second receiving container 22. The electrolyte in the second receiving container 22 is analyzed, and the infusible content is 0.0096wt%, and the infusible removal rate is 86.67%.

[0178] (3) Recycling: After secondary filtration, it returns to the metal lithium electrolytic cell 4 for reuse.

[0179] Example 2

[0180] This embodiment provides a circulating purification method for KCl-LiCl electrolyte, using Figure 4 The circulation system shown is processed, which includes:

[0181] (1) Online monitoring: Online monitoring shows that the content of infusible matter in the metal lithium electrolyte is 0.0265wt%, and the Ba in the electrolyte is 2 The content is 1.056wt%, Ca 2 The content is 0.2834wt%, and the contents of other impurities are all lower than the preset processing threshold.

[0182] (2) Curing agent treatment: The above electrolyte was transferred to a curing reaction vessel 2 with a mass of about 5 tons, and heated to 450°C for insulation. Then 115.8 kg of anhydrous potassium sulfate (the amount of curing agent is 90% of the theoretical amount) was added and stirred for reaction. The electrolyte melt changed from clear to milky white turbid. Then the electrolyte was heated to 600°C and kept for reaction for 5 hours. After the insulation was completed, the electrolyte was cooled to 410°C and the upper layer of the electrolyte was observed to be clear.

[0183] (3) Filtration and analysis: The electrolyte is filtered and the filtrate is analyzed.

[0184] (4) Recycling: The filtrate is returned to the metal lithium electrolytic cell 4.

[0185]

[0186] Example 3

[0187] This embodiment provides a circulating purification method for KCl-LiCl electrolyte, using Figure 4 The circulation system shown is processed, which includes:

[0188] (1) Online monitoring: Online monitoring shows that the content of infusible matter is 0.0251wt%, and Ba in the electrolyte is 2 and Ca 2The contents of all impurities are lower than the preset processing threshold, and the contents of one or more of the remaining impurities reach the preset processing threshold.

[0189] (2) Pre-electrolysis: The above electrolyte was transferred to the purification electrolytic cell 31, and the constant voltage power supply was turned on, the voltage was set to 2.9 V, the electrolysis temperature was set to 420° C., and the electrolysis was carried out for 3 h.

[0190] (3) Filtration: The electrolyte is filtered and the filtrate is sampled and analyzed, and the impurity ion content is lower than the treatment threshold.

[0191] (4) Recycling: The filtrate is returned to the metal lithium electrolytic cell 4.

[0192] The comparison of electrolyte impurities before and after treatment is shown in the following table:

[0193]

[0194] Example 4

[0195] This embodiment provides a circulating purification method for KCl-LiCl electrolyte, using Figure 4 The circulation system shown is processed, which includes:

[0196] (1) Online monitoring: Online monitoring shows that the content of infusible matter is 0.0179wt%, and Ba in the electrolyte is 2 The content is 0.8219wt%, Ca 2+ The content is 0.3476wt%, and the content of one or more of the remaining impurities reaches the preset processing threshold.

[0197] (2) Curing treatment: The above electrolyte was transferred to the curing reaction vessel 2, with a mass of about 4.9 tons, and heated to 455°C for insulation. Then, 140.6 kg of anhydrous potassium sulfate (the amount of curing agent is 110% of the theoretical amount) was added and stirred for reaction. The electrolyte melt changed from clear to milky white turbid. Then, the electrolyte was heated to 650°C and kept for reaction for 5 hours. After the insulation was completed, the electrolyte was cooled to 440°C and the upper layer of the electrolyte was observed to be clear.

[0198] (3) Pre-electrolysis: The above electrolyte was transferred to the purification electrolytic cell 31, and the constant voltage power supply was turned on, the voltage was set to 3V, the electrolysis temperature was set to 430°C, and the electrolysis was carried out for 2.8 hours.

[0199] (4) Filtration: After filtering the electrolyte, a filtrate and a filter residue are obtained, and the filtrate is analyzed.

[0200] (5) Recycling: The filtrate is returned to the production electrolytic cell.

[0201] Electrolyte Ba2 / Ca2 before and after treatment + The impurities comparison is as follows:

[0202]

[0203] The comparison of other cationic impurities in the electrolyte before and after treatment is shown in the following table:

[0204]

[0205] Example 5

[0206] This embodiment provides a circulating purification method for KCl-LiCl electrolyte, using Figure 4 The circulation system shown is processed, which includes:

[0207] (1) Online monitoring: Online monitoring shows that the infusible content is 0.0856wt%, Ba 2+ The content is 0.9627wt%, Ca 2 The content of other impurities is lower than the preset processing threshold, and the content of other impurities does not reach the preset processing threshold.

[0208] (2) Multi-stage filtration: Installation Figure 2 and Figure 3 The high-temperature molten salt filtration system 1 shown performs a primary filtration (filtration aperture of 40 μm, filtration temperature of 460°C) to allow the abnormal electrolyte to enter the first receiving container 12, and then performs a secondary filtration (filtration aperture of 15 μm, filtration temperature of 455°C) to allow the electrolyte to enter the second receiving container 22. The electrolyte in the second receiving container 22 is taken for analysis, and the infusible content is obtained to be 0.0116wt%, and the infusible removal rate is 86.45%.

[0209] (3) Curing treatment: The above electrolyte was transferred to the curing reaction vessel 2, with a mass of about 4.9 tons, and heated to 450°C for insulation. Then 37.8 kg of anhydrous lithium sulfate (the amount of curing agent is 100% of the theoretical amount) was added and stirred for reaction. The electrolyte melt changed from clear to milky white turbid. Then the electrolyte was heated to 750°C and kept for reaction for 4.6 hours. After the insulation was completed, the electrolyte was cooled to 450°C and the upper layer of the electrolyte was observed to be clear.

[0210] (4) Filtration: After filtering the electrolyte, a filtrate and a filter residue are obtained, and the filtrate is analyzed.

[0211] (5) Recycling: The filtrate is returned to the production electrolytic cell.

[0212] Electrolyte Ba before and after treatment 2 The impurity comparison is shown in the following table

[0213]

[0214]

[0215] Example 6

[0216] This embodiment provides a circulating purification method for KCl-LiCl electrolyte, using Figure 4 The circulation system shown is processed, which includes:

[0217] (1) Online monitoring: Online monitoring shows that the infusible content is 0.0827wt%, Ba 2+ and Ca2 are lower than the preset processing threshold, and the contents of one or more of the remaining impurities reach the preset processing threshold.

[0218] (2) Multi-stage filtration: Installation Figure 2 and Figure 3 The high-temperature molten salt filtration system 1 shown performs a primary filtration (filtration pore size of 30 μm, filtration temperature of 470°C) to allow the abnormal electrolyte to enter the first receiving container 12, and then performs a secondary filtration (filtration pore size of 5 μm, filtration temperature of 460°C) to allow the electrolyte to enter the second receiving container 22. The electrolyte in the second receiving container 22 is taken for analysis, and the infusible content is obtained to be 0.0124wt%, and the infusible removal rate is 85.01%.

[0219] (3) Pre-electrolysis: The filtered electrolyte was transferred to the purification electrolytic cell 31, and the constant voltage power supply was turned on, the voltage was set to 2.50 V, the electrolysis temperature was set to 428° C., and the electrolysis was carried out for 3.5 h.

[0220] (4) Filtration: After filtering the electrolyte, a filtrate and a filter residue are obtained. The filtrate is analyzed and the impurity ion content is lower than the treatment threshold.

[0221] (5) Recycling: The filtrate is returned to the metal lithium electrolytic cell 4.

[0222] The comparison of other cationic impurities in the electrolyte before and after treatment is shown in the following table:

[0223]

[0224] Example 7

[0225] This embodiment provides a circulating purification method for KCl-LiCl electrolyte, using Figure 4 The circulation system shown is processed, which includes:

[0226] (1) Online monitoring: Online monitoring shows that the infusible content is 0.0623wt%, Ba 2+ The content is 0.9211wt%, Ca 2+ The content is 0.3182wt%, and the content of one or more of the remaining impurities reaches the preset processing threshold.

[0227] (2) Multi-stage filtration: Installation Figure 2 and Figure 3 The high-temperature molten salt filtration system 1 shown performs a primary filtration (filtration aperture of 40 μm, filtration temperature of 445°C) to allow the abnormal electrolyte to enter the first receiving container 12, and then performs a secondary filtration (filtration aperture of 10 μm, filtration temperature of 440°C) to allow the electrolyte to enter the second receiving container 22. The electrolyte in the second receiving container 22 is taken for analysis, and the infusible content is obtained to be 0.0102wt%, and the infusible removal rate is 83.63%.

[0228] (3) Curing treatment: The above electrolyte was transferred to the curing reaction vessel 2, with a mass of about 5.2 tons, and heated to 430°C for insulation. Then 88.2 kg of anhydrous lithium sulfate (the amount of curing agent is 105% of the theoretical amount) was added and stirred for reaction. The electrolyte melt changed from clear to milky white turbid. Then the electrolyte was heated to 870°C and kept for reaction for 5 hours. After the insulation was completed, the electrolyte was cooled to 410°C and the upper layer of the electrolyte was observed to be clear.

[0229] (4) Pre-electrolysis: The solidified electrolyte is transferred to the purification electrolytic cell 31, and the constant voltage power supply is turned on, the voltage is set to 2.9 V, the electrolysis temperature is 420° C., and the electrolysis is performed for 3 h.

[0230] (5) Filtration and analysis: After filtering the electrolyte, a filtrate and a filter residue are obtained, and the filtrate is analyzed.

[0231] (6) Recycling: The filtrate is returned to the metal lithium electrolytic cell 4.

[0232] Electrolyte Ba2 / Ca2 before and after treatment + The impurities comparison is as follows:

[0233]

[0234] The comparison of other cationic impurities in the electrolyte before and after treatment is shown in the following table:

[0235]

[0236] Example 8

[0237] This embodiment provides a circulating purification method for KCl-LiCl electrolyte, using Figure 4 The circulation system shown is processed, which includes:

[0238] (1) Online monitoring: Online monitoring shows SO4 in KCl-LiCl electrolyte raw materials 2- / CO3 2- / SiO3 2- / BO3 3-One or more of the acid radicals reaches the preset processing threshold (the preset processing threshold corresponding to each ion: SO4 2- 0.015wt%,CO3 2- 0.01wt%, SiO3 2- 0.01wt%, BO3 3- is 0.01wt%).

[0239] (2) Pre-electrolysis: The electrolyte was transferred to the purification electrolytic cell 31, and the constant voltage power supply was turned on, the voltage was set to 3 V, the electrolysis temperature was set to 415° C., and the electrolysis was performed for 2.5 h.

[0240] (3) Filtration: After filtering the electrolyte, a filtrate and a filter residue are obtained. The filtrate is analyzed and the impurity ion content is lower than the treatment threshold.

[0241] (4) Recycling: The filtrate is returned to the metal lithium electrolytic cell 4.

[0242] The comparison of impurity content before and after electrolyte raw material treatment is shown in the following table.

[0243] Impurity Type <![CDATA[SO4 2- ]]> <![CDATA[CO3 2- ]]> <![CDATA[SiO3 2- ]]> <![CDATA[BO3 3- ]]> Content before treatment (wt%) 0.01 0.21 0.0056 0.0064 Content after treatment (wt%) 0.0035 0.0039 0.0027 0.0025

[0244] Example 9

[0245] This embodiment provides a circulating purification method for KCl-LiCl electrolyte, using Figure 4 The circulation system shown is processed, which includes:

[0246] (1) Online monitoring: Online monitoring shows that the infusible content in the KCl-LiCl electrolyte is 0.0825wt%, and the Ba in the electrolyte is 2 / Ca 2 The contents of other impurities are all below the preset processing threshold.

[0247] (2) Filtering and analysis: Installation Figure 2 and Figure 3 The high-temperature molten salt filtration system 1 shown in the figure performs primary filtration (filtration aperture of 90 μm, filtration temperature of 450°C) to allow abnormal electrolyte to enter the first receiving container 12. Secondary filtration (filtration aperture of 25 μm, filtration temperature of 450°C) is performed again to allow electrolyte to enter the second receiving container 22. The electrolyte in the second receiving container 22 is analyzed, and the infusible content is 0.0166wt%, and the infusible removal rate is 79.88%.

[0248] (3) Recycling: After secondary filtration, it returns to the metal lithium electrolytic cell 4 for reuse.

[0249] Example 10

[0250] This embodiment provides a circulating purification method for KCl-LiCl electrolyte, using Figure 4 The circulation system shown is processed, which includes:

[0251] (1) Online monitoring: Online monitoring shows that the content of infusible matter in the metal lithium electrolyte is 0.0165wt%, and the Ba in the electrolyte is 2 The content is 0.9267wt%, Ca 2 The content is 0.2541wt%, and the contents of other impurities are all lower than the preset processing threshold.

[0252] (2) Curing treatment: The above electrolyte was transferred to a curing reaction vessel 2 with a mass of about 5 tons, and heated to 450°C for insulation. Then 71.7 kg of anhydrous sodium phosphate (the amount of curing agent is 100% of theory) was added and stirred for reaction. The electrolyte melt changed from clear to milky white turbid. Then the electrolyte was heated to 450°C and kept for reaction for 4 hours. After the insulation was completed, the electrolyte was cooled to 415°C and the upper layer of the electrolyte was observed to be clear.

[0253] (3) Filtration and analysis: The electrolyte is filtered and the filtrate is analyzed.

[0254] (4) Recycling: The filtrate is returned to the metal lithium electrolytic cell 4.

[0255]

[0256] Embodiment 11

[0257] This embodiment provides a circulating purification method for KCl-LiCl electrolyte, using Figure 4 The difference from the above embodiment is that in addition to monitoring the ionic impurities in the above embodiment, this embodiment also monitors the introduction of SO4 into the curing agent after curing. 2- or PO4 3- Impurities, including:

[0258] (1) Online monitoring: Online monitoring shows that the content of infusible matter in the electrolyte is 0.0142wt%, and the Ba in the electrolyte is 2 The content is 0.9678wt%, Ca 2 The content is 0.2771wt%, and the contents of other impurities are all lower than the preset processing threshold.

[0259] (2) Curing treatment: The above electrolyte was transferred to the curing reaction vessel 2, with a mass of about 5.1 tons, and heated to 430°C for insulation. Then 115.4 kg of anhydrous lithium sulfate (the amount of curing agent is 160% of the theoretical amount) was added and stirred for reaction. The electrolyte melt changed from clear to milky white turbid. Then the electrolyte was heated to 650°C and kept for reaction for 4.5 hours. After the insulation was completed, the electrolyte was cooled to 415°C and the upper layer of the electrolyte was observed to be clear. After filtration, sulfate was detected, and the sulfate content was 471 ppm.

[0260] (3) Pre-electrolysis: The filtered electrolyte was transferred to the purification electrolytic cell 31, and the constant voltage power supply was turned on, the voltage was set to 2.95 V, the electrolysis temperature was set to 428° C., and the electrolysis was carried out for 3.5 h.

[0261] (4) Filtration and analysis: After filtering the electrolyte, a filtrate and a filter residue are obtained. The filtrate is analyzed and the impurity ion content is lower than the treatment threshold.

[0262] (5) Recycling: The filtrate is returned to the metal lithium electrolytic cell 4.

[0263] The comparison of electrolyte impurities before and after treatment is shown in the following table:

[0264]

[0265] Comparative Example 1

[0266] The difference between this comparative example and Example 1 is that the aperture of the primary filter is 200 μm, and the aperture of the secondary filter is 50 μm.

[0267] Before treatment: infusible matter content: 0.0786wt%, and the remaining impurity content is lower than the preset treatment threshold.

[0268] After treatment: unmelted matter content: 0.0399wt%, unmelted matter removal rate: 50.76%.

[0269] Comparative Example 2

[0270] The difference between this comparative example and Example 2 is that the mass of the added curing agent (potassium sulfate) is 50% of the theoretical amount.

[0271] Before treatment: Ba 2 The content is 0.8836wt%, Ca 2 The content is 0.0279wt%, and the content of other impurities is lower than the preset processing threshold.

[0272] After treatment: Ba 2 The content is 0.4467wt%, Ca 2 Content: 0.0236wt%

[0273] Electrolyte Ba before and after treatment 2 / Ca 2+ The impurities comparison is as follows:

[0274]

[0275] Comparative Example 3

[0276] The difference between this comparative example and Example 3 is that the pre-electrolysis voltage is 0.3V.

[0277] The comparison table of impurities in the electrolyte before and after treatment is as follows:

[0278]

[0279] Comparative Example 4

[0280] The difference between this comparative example and Example 7 is that after abnormal electrolyte data is detected, pre-electrolysis is first performed, followed by multi-stage filtration, then solidification treatment, and finally recycling. The data before and after the treatment of various impurities in the electrolyte are as follows.

[0281] Electrolyte infusible matter and Ba before and after treatment 2 / Ca 2+ The impurities comparison is as follows:

[0282]

[0283] Other cation data are as follows:

[0284]

[0285] Comparative Example 5

[0286] The difference between this comparative example and Example 7 is that after abnormal electrolyte data is detected, solidification is first performed, followed by pre-electrolysis filtration, multi-stage filtration, and finally recycling. The data before and after the treatment of various impurities in the electrolyte are as follows.

[0287] Electrolyte infusible matter and Ba before and after treatment 2 / Ca 2+ The impurities comparison is as follows:

[0288]

[0289] Other cation data are as follows:

[0290]

[0291] In summary, the embodiments of the present invention provide a lithium electrolyte impurity removal system and method with the advantages of being simple and efficient, having a large processing volume, obvious effect, and a high safety factor, which has the following advantages:

[0292] (1) Efficient integrated process: Compared with the traditional water-soluble method and dilution method, this impurity removal process realizes continuous operation of the entire process, greatly simplifies the equipment and operation steps, and is convenient and efficient to operate. Its powerful processing capacity can remove up to 13 impurities at one time, with a single processing capacity of up to 4 to 5 tons of electrolyte, significantly improving production efficiency.

[0293] (2) Quality improvement and cost savings: This process can significantly optimize the purity of lithium metal, achieving an excellent result of reducing impurity content by more than 80%, which directly improves the market competitiveness of the product. At the same time, by extending the service life of the electrolytic cell to an average of about 350 days (about 70 days more than before), the frequency of equipment replacement and maintenance is greatly reduced, thereby achieving significant cost savings and economic benefits.

[0294] (3) Green, safe and eco-friendly: The entire processing process adheres to the concept of green and safe production, produces almost no emissions of toxic and hazardous substances, and has minimal impact on the environment and employee health. It perfectly fits the sustainable development strategy and demonstrates a high sense of social responsibility and environmental awareness.

[0295] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A circulating purification method for KCl-LiCl electrolyte, characterized in that: It includes: S1. In the process of preparing metallic lithium by electrolysis, the contents of infusible materials, high potential ions and low potential ions of the KCl-LiCl electrolyte in the metallic lithium electrolytic cell are monitored, and it is determined whether the content of the infusible materials reaches or exceeds a preset infusible material processing threshold, whether the content of one or more of the high potential ions reaches or exceeds a corresponding preset processing threshold, and whether the content of one or more of the low potential ions reaches or exceeds a corresponding preset processing threshold; S2. Remove impurities according to the monitoring results in the order of priority: infusible materials, high potential ions, and low potential ions: If the content of the infusible matter reaches or exceeds the preset infusible matter processing threshold, the electrolyte in the metal lithium electrolytic cell is first subjected to multi-stage filtration to remove the infusible matter; If the content of one or more of the high-potential ions reaches or exceeds the corresponding preset processing threshold, a curing agent is added to the electrolyte from which the infusibles are removed by multi-stage filtration or the electrolyte in which the monitoring result shows that the infusibles are less than the preset infusible processing threshold, so as to remove the high-potential ions; If one or more contents of the low-potential ions reach or exceed the corresponding preset processing threshold, an electrolyte that removes the infusible material and / or the high-potential ions or an electrolyte whose detection results show that the infusible material and the high-potential ions are respectively less than the preset infusible material processing threshold and the preset processing threshold corresponding to the high-potential ions is introduced into the pre-electrolysis tank for constant-voltage electrolysis to remove the low-potential ions; S3, filtering the electrolyte after removing impurities and transferring it to the metal lithium electrolytic cell for continued use.

2. The circulating purification method of KCl-LiCl electrolyte according to claim 1, characterized in that: The frequency of monitoring the contents of the infusible matter, the high potential ions, and the low potential ions in the electrolyte in the metal lithium electrolytic cell is 5 to 20 days per time.

3. The circulating purification method of KCl-LiCl electrolyte according to claim 1, characterized in that: The high potential ions include Ba 2+ and / or Ca 2+ , the low potential ions include SO4 2- 、CO3 2- 、SiO3 2- , BO3 3- PO4 3- Mg 2+ , Fe 2+ 、Al 3+ 、Ni 2+ Cr 3+ and Pb 2+ At least one of; Preferably, the high potential ions include Ba 2+ and Ca 2+ The low potential ions include at least Mg 2+ , Fe 2+ 、Al 3+ 、Ni 2 + Cr 3+ and Pb 2+ More preferably, the high potential ions include Ba 2+ and Ca 2+ , the low potential ions include SO4 2- 、CO3 2- 、SiO3 2- , BO3 3- PO4 3- Mg 2+ , Fe 2+ 、Al 3+ 、Ni 2+ Cr 3+ and Pb 2+ .

4. The circulating purification method of KCl-LiCl electrolyte according to claim 3, characterized in that: The preset infusible material processing threshold is selected from 0.04wt% to 0.06wt%; And / or, the Ba 2+ The corresponding preset processing threshold is selected from 0.25wt% to 0.35wt%; and / or, the Ca 2+ The corresponding preset processing threshold is selected from 0.1wt% to 0.14wt%; And / or, the Mg 2+ The corresponding preset processing threshold is selected from 0.02wt% to 0.04wt%; And / or, the Fe 2+ The corresponding preset processing threshold is selected from 0.008wt% to 0.012wt%; And / or, the Al 3+ The corresponding preset processing threshold is selected from 0.008wt% to 0.012wt%; and / or, the Ni 2+ The corresponding preset processing threshold is selected from 0.002wt% to 0.004wt%; and / or, the Cr 3+ The corresponding preset processing threshold is selected from 0.002wt% to 0.004wt%; and / or, the Pb 2+ The corresponding preset processing threshold is selected from 0.002wt% to 0.004wt%; and / or, the SO4 2- The corresponding preset processing threshold is selected from 0.01wt% to 0.02wt%; and / or, the CO3 2- The corresponding preset processing threshold is selected from 0.008wt% to 0.012wt%; And / or, the SiO3 2- The corresponding preset processing threshold is selected from 0.008wt% to 0.012wt%; and / or, the BO3 3- The corresponding preset processing threshold is selected from 0.008wt% to 0.012wt%; and / or, the PO4 3- The corresponding preset processing threshold is selected from 0.008wt% to 0.012wt%.

5. The circulating purification method of KCl-LiCl electrolyte according to claim 4, characterized in that: The preset infusible material processing threshold is 0.05wt%; And / or, the Ba 2+ The corresponding preset treatment threshold is 0.3wt%; and / or, the Ca 2+ The corresponding preset treatment threshold is 0.1wt%; And / or, the Mg 2+ The corresponding preset treatment threshold is 0.03wt%; And / or, the Fe 2+ The corresponding preset treatment threshold is 0.01wt%; And / or, the Al 3+ The corresponding preset treatment threshold is 0.01wt%; and / or, the Ni 2+ The corresponding preset treatment threshold is 0.003wt%; and / or, the Cr 3+ The corresponding preset treatment threshold is 0.003wt%; and / or, the Pb 2+ The corresponding preset treatment threshold is 0.003wt%; and / or, the SO4 2- The corresponding preset treatment threshold is selected from 0.015wt%; and / or, the CO3 2- The corresponding preset processing threshold is selected from 0.01wt%; And / or, the SiO3 2- The corresponding preset processing threshold is selected from 0.01wt%; and / or, the BO3 3- The corresponding preset processing threshold is selected from 0.01wt%; and / or, the PO4 3- The corresponding preset processing threshold is selected from 0.01 wt %.

6. The circulating purification method of KCl-LiCl electrolyte according to claim 1, characterized in that: Multi-stage filtration is two-stage filtration, wherein the temperature of the first-stage filtration is 400℃~700℃, the pore size of the filter mesh is 30μm~100μm, and the temperature of the second-stage filtration is 400℃~700℃, the pore size of the filter mesh is 1μm~30μm.

7. The circulating purification method of KCl-LiCl electrolyte according to claim 6, characterized in that: The temperature of the first-stage filtration is 440°C to 460°C, the aperture of the filter mesh is 30μm to 50μm, the temperature of the second-stage filtration is 440°C to 460°C, and the aperture of the filter mesh is 5μm to 15μm.

8. The circulating purification method of KCl-LiCl electrolyte according to claim 6, characterized in that: Multi-stage filtration uses a high-temperature molten salt filtration system for filtration, and the high-temperature molten salt filtration system includes a first filtration device and a second filtration device. The first filtration device at least includes a molten salt feeding pipe, a first material receiving container and a first filtering mechanism. The first filtering mechanism is arranged between the molten salt feeding pipe and the first material receiving container, so that the molten salt in the molten salt feeding pipe enters the first material receiving container after being filtered by the first filtering mechanism. The second filtration device includes a molten salt conveying pipe connected to the first material receiving container, a second material receiving container and a second filtering mechanism. The second filtering mechanism is arranged between the molten salt conveying pipe and the second material receiving container, so that the molten salt in the first material receiving container enters the second material receiving container after being filtered by the second filtering mechanism.

9. The circulating purification method of KCl-LiCl electrolyte according to claim 8, characterized in that: The first filter mechanism and the second filter mechanism both include a cylinder, a filter screen, a wire brush in contact with the filter screen, a rotating support shaft and arc-shaped fan blades. One end of the cylinder is connected to a pipe at the top, and the other end of the cylinder is provided with the filter screen and is connected to the first material receiving container or the second material receiving container at the bottom. The rotating support shaft is coaxially installed inside the cylinder and the axis of the rotating support shaft is perpendicular to the mesh surface of the filter screen. The wire brush and the arc-shaped fan blades are both fixedly connected to the axial direction of the rotating support shaft, and the arc-shaped fan blades are fixedly connected to one end of the rotating support shaft relatively away from the filter screen.

10. The circulating purification method of KCl-LiCl electrolyte according to claim 8, characterized in that: The first filtering device further includes a first sealed material storage tank and a first pressurizing assembly, the molten salt feed pipe is connected to the first sealed material storage tank, the bottom of the first sealed material storage tank is connected to the first material receiving container through a pipeline, the first filtering mechanism is arranged at the connection between the first material receiving container and the feed pipeline, the first pressurizing assembly includes a first pressurizing pipeline, a first pressurizing pump and a first pressure gauge, one end of the first pressurizing pipeline is connected to the first sealed material storage tank, and the other end is connected to the first pressurizing pump, and the first pressurizing pipeline is provided with the first pressure gauge; And / or, the second filtering device also includes a second sealed storage tank and a second pressurizing component, the molten salt delivery pipeline is connected to the second sealed storage tank, the bottom of the second sealed storage tank is connected to the second material receiving container through a pipeline, the second filtering mechanism is arranged at the connection between the second material receiving container and the feed pipeline, the second pressurizing component includes a second pressurizing pipeline, a second pressurizing pump and a second pressure gauge, one end of the second pressurizing pipeline is connected to the second sealed storage tank, and the other end is connected to the second pressurizing pump, and the second pressurizing pipeline is provided with the second pressure gauge.

11. The circulating purification method of KCl-LiCl electrolyte according to claim 10, characterized in that: The molten salt feeding pipe and / or the molten salt conveying pipe is provided with a heating device.

12. The circulating purification method of KCl-LiCl electrolyte according to claim 10, characterized in that: The first filtering device and the second filtering device are both provided with a material inlet and outlet control device.

13. The circulating purification method of KCl-LiCl electrolyte according to claim 1, characterized in that: The curing agent is sulfate or phosphate, the sulfate is selected from one or more of potassium sulfate, lithium sulfate and sodium sulfate, and the phosphate is sodium phosphate.

14. The circulating purification method of KCl-LiCl electrolyte according to claim 13, characterized in that: The ratio of the molar amount of the added curing agent to the total molar amount of the high-potential ions is (0.9-1.4):1, preferably (1-1.2):

1.

15. The circulating purification method of KCl-LiCl electrolyte according to claim 14, characterized in that: When adding the curing agent, the temperature of the electrolyte is controlled to be 400°C to 500°C. After adding the curing agent, the temperature is maintained at 400°C to 1000°C, and the reaction is kept warm for 3 to 5 hours. Preferably, after adding the curing agent, the temperature is maintained at 400°C to 500°C. Preferably, after the heat preservation reaction, the temperature is controlled to 400° C. to 500° C. for sedimentation.

16. The circulating purification method of KCl-LiCl electrolyte according to claim 1, characterized in that: The ratio of the molar amount of the added curing agent to the total molar amount of the high-potential ions is greater than 1.4:1, and the KCl-LiCl electrolyte is electrolyzed at a constant voltage after curing and separation.

17. The circulating purification method of KCl-LiCl electrolyte according to claim 1 or 16, characterized in that: The voltage of the constant voltage electrolysis is 1V to 3V, preferably 2V to 3V; And / or, the temperature of the constant voltage electrolysis is 420°C to 480°C, preferably 420°C to 430°C.

18. The circulating purification method of KCl-LiCl electrolyte according to any one of claims 1 to 16, characterized in that: Before step S3, the electrolyte from which impurities have been removed is tested and analyzed to see whether it satisfies the following conditions: (1) The content of the infusible material is less than a preset infusible material processing threshold; (2) the contents of various impurities in the high-potential ions are all less than the corresponding preset processing thresholds; (3) the contents of various impurities in the low-potential ions are all less than the corresponding preset processing thresholds; If the condition is met, proceed to step S3; if not, loop through step S2.

19. The circulating purification method of KCl-LiCl electrolyte according to any one of claims 1 to 16, characterized in that: Before the KCl-LiCl electrolyte raw material is introduced into the metal lithium electrolytic cell, SO4 in the KCl-LiCl electrolyte raw material is detected. 2- 、CO3 2- 、SiO3 2- or BO3 3- Whether at least one reaches above the corresponding preset processing threshold, if so, it is passed into the pre-electrolysis tank for pre-electrolysis.

20. The circulating purification method of KCl-LiCl electrolyte according to claim 18, characterized in that: The voltage of the pre-electrolysis is 1V to 3V, preferably 2V to 3V; And / or, the pre-electrolysis temperature is 420°C to 480°C, preferably 420°C to 430°C.

21. The circulating purification method of KCl-LiCl electrolyte according to claim 18, characterized in that: SO4 in the KCl-LiCl electrolyte raw material 2- The preset treatment threshold is selected from 0.01wt% to 0.02wt%, preferably 0.015wt%; And / or, CO3 in the KCl-LiCl electrolyte raw material 2- The preset treatment threshold is selected from 0.008wt% to 0.012wt%, preferably 0.01wt%; And / or, SiO3 in the KCl-LiCl electrolyte raw material 2- The preset treatment threshold is selected from 0.008wt% to 0.012wt%, preferably 0.01wt%; And / or, BO3 in the KCl-LiCl electrolyte raw material 3- The preset treatment threshold is selected from 0.008 wt % to 0.012 wt %, preferably 0.01 wt %.

22. A KCl-LiCl electrolyte circulation purification system, characterized in that: It includes a high-temperature molten salt filtration system, a solidification reaction container, an electrochemical purification system and a metal lithium electrolytic cell. The high-temperature molten salt filtration system, the solidification reaction container, the electrochemical purification system and the metal lithium electrolytic cell are connected in series in sequence, and the discharge port of the high-temperature molten salt filtration system, the discharge port of the solidification reaction container and the discharge port of the electrochemical purification system are respectively connected to the feed port pipeline of the metal lithium electrolytic cell, and the feed port of the high-temperature molten salt filtration system, the feed port of the solidification reaction container and the feed port of the electrochemical purification system are respectively connected to the discharge port of the metal lithium electrolytic cell.

23. The KCl-LiCl electrolyte circulation purification system according to claim 22, characterized in that: It also includes a raw material inlet pipe, and the electrochemical purification system and the metal lithium electrolytic cell are both connected to the raw material inlet pipe.

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