Method for removing impurities from lithium sulfate back-extraction solution, lithium sulfate solution, lithium compound-containing solution and applications

Abstract

The application provides a method for removing impurities from lithium sulfate back-extraction solution, a lithium sulfate solution, a lithium compound and an application. The method comprises the following steps: firstly mixing lithium sulfate back-extraction solution, a first impurity removal agent and a second impurity removal agent to obtain a mixed solution; secondly adjusting the pH value of the mixed solution to be acidic, and obtaining a first filtrate and a first filter residue after the first reaction, wherein the first impurity removal agent comprises a sulfuration agent, and the second impurity removal agent comprises a calcium removal agent; thirdly adjusting the pH value of the first filtrate to be alkaline, and obtaining a second filtrate and a second filter residue after the second reaction; and fourthly further processing the second filtrate to obtain a purified lithium sulfate solution. The impurity removal method provided by the application can greatly reduce the concentration of divalent cation impurities such as copper, iron, calcium and magnesium in the lithium sulfate back-extraction solution, so that the purified lithium sulfate solution can meet the process requirements of a bipolar membrane system for preparing lithium-containing products, and thus the large-scale production of high-purity and high-efficiency lithium-containing products can be realized.

Description

Technical Field

[0001] This invention belongs to the field of solution purification and upgrading technology in hydrometallurgical processes, specifically relating to a method for removing impurities from lithium sulfate back-extraction solution, lithium sulfate solution, lithium-containing compounds, and their applications. Background Technology

[0002] Lithium (Li) is a silvery-white, light metal with a high oxidation potential, widely used in batteries and energy storage. With the rapid development of the new energy electric vehicle industry, lithium consumption has increased dramatically. Currently, the main sources of lithium include lithium extraction from salt lakes, mining, and recycling of spent lithium batteries. The lithium extraction process typically uses hydrometallurgical processes to convert lithium-containing materials into a lithium-containing solution. However, on the one hand, the lithium-containing materials contain a large number of impurity elements (such as calcium and magnesium ions in salt lake brine and copper and iron ions in spent lithium batteries), resulting in low purity of the lithium sulfate solution. On the other hand, lithium sulfate solution cannot be directly used as a raw material for preparing power batteries and needs to be transformed into products such as lithium carbonate and lithium hydroxide. Especially in the process of preparing high-purity lithium-containing solutions from lithium sulfate using bipolar membrane electrodialysis, the concentration of divalent cations in the solution is extremely critical. The presence of excessive calcium and magnesium ions can lead to scaling and fouling of the bipolar membrane, resulting in a sharp decline in membrane performance, soaring energy consumption, reduced efficiency, and unstable product quality. Therefore, in order to obtain high-purity lithium-containing raw materials, deep impurity removal treatment of the lithium sulfate solution is necessary during the transformation process.

[0003] Existing technologies disclose numerous technical solutions for purifying lithium sulfate solutions. For example, CN110451535A discloses a method for purifying and removing impurities from lithium sulfate solutions, which uses calcium peroxide or other oxidants to remove impurities containing Fe. 2+ Ni 2 + Co 2+ Mn 2+ and F - The method involves removing impurities from a lithium sulfate solution, but this introduces additional calcium ion impurities. Furthermore, the concentration of divalent cation impurities in the purified lithium sulfate solution is greater than 1 mg / L, which completely fails to meet the feed requirements for preparing lithium-containing products using bipolar membrane electrodialysis. CN116443900A discloses a method for removing calcium from a lithium sulfate solution, using a combination of sodium carbonate and a complexing agent to remove calcium impurities and prepare lithium carbonate products. However, due to the low solubility of lithium carbonate, the above method results in the loss of lithium ions during calcium removal, and the concentration of calcium ions in the solution remains approximately 40 mg / L, far from meeting the feed requirements for preparing lithium-containing products using bipolar membrane electrodialysis.

[0004] Therefore, there is an urgent need in this field to develop a method for deep purification of lithium sulfate solutions in order to solve the above problems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for removing impurities from lithium sulfate back-extraction solution, as well as a lithium sulfate solution, lithium-containing compounds, and their applications. The impurity removal method provided by this invention can significantly reduce the concentration of divalent cation impurities such as copper, iron, calcium, and magnesium in the lithium sulfate back-extraction solution, enabling the purified lithium sulfate solution to meet the process requirements for preparing lithium-containing products using a bipolar membrane system. This allows for the large-scale production of high-purity, high-efficiency lithium-containing products.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for removing impurities from a lithium sulfate back-extraction solution, the method comprising the following steps:

[0008] S1. A mixed solution is obtained by mixing lithium sulfate back-extraction solution, a first impurity remover, and a second impurity remover; the pH of the mixed solution is adjusted to acidic for the first time, and a first filtrate and a first filter residue are obtained after the first reaction, wherein the first impurity remover includes a sulfiding agent, and the second impurity remover includes a calcium removal agent;

[0009] S2. Adjust the pH of the first filtrate to alkaline for the second time, and obtain the second filtrate and the second filter residue after the second reaction;

[0010] S3. The second filtrate is further processed to obtain a purified lithium sulfate solution.

[0011] Currently, during the lithium extraction process, some divalent cation impurities such as copper, iron, calcium, and magnesium enter the extraction solution. In order to remove these impurity ions and ensure that the lithium sulfate extraction solution meets the process requirements for preparing lithium-containing products using a bipolar membrane system, this invention first uses a combination of a first impurity remover and a second impurity remover to remove copper ions, iron ions, and most of the calcium ions in the solution. Then, the pH value of the first filtrate is further adjusted to alkaline to remove most of the magnesium ions in the solution. Finally, a further impurity removal process is combined to solve the technical problem of the difficulty in deeply removing divalent cation impurities such as copper, iron, calcium, and magnesium from the lithium sulfate extraction solution.

[0012] Furthermore, the concentration of divalent cations such as copper, iron, calcium, and magnesium in the purified lithium sulfate solution of this invention can be reduced to below 1 mg / L, thus meeting the feed requirements for the preparation of high-purity lithium-containing products by bipolar membrane systems.

[0013] Preferably, in step S1, the lithium sulfate back-extraction solution includes a first impurity ion, a second impurity ion, and a third impurity ion.

[0014] Preferably, the first impurity ions include copper ions and / or iron ions. This is mainly because during the recycling of waste lithium batteries, especially waste lithium iron phosphate batteries, the lithium iron phosphate cathode material is coated on the surface of copper foil. Copper will enter the black powder as the waste battery is broken up. In the subsequent hydrometallurgical lithium extraction process, copper and iron impurities will also enter the lithium-containing solution.

[0015] Preferably, in the lithium sulfate back-extraction solution, the concentrations of copper ions and iron ions are each independently less than 500 mg / L, for example, 50 mg / L, 100 mg / L, 200 mg / L, 300 mg / L, 400 mg / L or 500 mg / L, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0016] Preferably, the second impurity ion includes calcium ions.

[0017] Preferably, the third impurity ion includes magnesium ions.

[0018] In this invention, the main reason for the generation of calcium and magnesium ion impurities is that the concentration of calcium and magnesium ions in the brine is very high. During the lithium extraction process, they are easily introduced into the solution along with the lithium, resulting in some calcium and magnesium ions entering the back-extraction solution during the lithium extraction process.

[0019] Preferably, in the lithium sulfate back-extraction solution, the concentrations of calcium ions and magnesium ions are each independently less than 500 mg / L, for example, 50 mg / L, 100 mg / L, 200 mg / L, 300 mg / L, 400 mg / L or 500 mg / L, etc., and are not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Preferably, in step S1, the lithium sulfate back-extraction solution further includes lithium ions.

[0021] Preferably, the concentration of lithium ions in the lithium sulfate back-extraction solution is ≥5 g / L, for example, it can be 5 g / L, 8 g / L, 10 g / L, 12 g / L, 15 g / L, 18 g / L, 20 g / L or 25 g / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] Preferably, in step S1, the pH value of the lithium sulfate back-extraction solution is ≤2, for example, it can be 0.8, 1, 1.2, 1.5, 1.8 or 2, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0023] Preferably, in step S1, the sulfiding agent includes sodium sulfide. The present invention utilizes a sulfiding agent precipitation method to effectively remove copper and / or iron ion impurities from lithium sulfate back-extraction solutions. The specific reaction principle is as follows:

[0024] Cu 2+ +S 2- =CuS↓;

[0025] Fe 2+ +S 2- =FeS↓.

[0026] Preferably, the mass ratio of the first impurity remover to the first impurity ion is (2-18):1, for example, it can be 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 12:1, 15:1 or 18:1, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] In this invention, the first impurity ion is effectively removed by adjusting the mass ratio of the first impurity remover to the first impurity ion. If a lower content of the first impurity remover is used, the concentration of the first impurity ion in the lithium sulfate back-extraction solution cannot be significantly reduced; if a higher content of the first impurity remover is used, other impurity ions are easily introduced, thereby affecting the purity of the lithium-containing product.

[0028] Preferably, in step S1, the calcium removal agent includes oxalic acid and / or oxalate, with oxalic acid being the most preferred. This invention removes most of the calcium ions from the lithium sulfate back-extraction solution by selecting an oxalic acid-based calcium removal agent. The specific reaction principle is as follows:

[0029] Ca 2+ +C2O4 2- =CaC2O4↓.

[0030] Preferably, the oxalate comprises sodium oxalate and / or lithium oxalate.

[0031] Preferably, the mass ratio of the second impurity remover to the second impurity ion is (4-12):1, for example, it can be 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1 or 12:1, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] In this invention, the second impurity ion can be effectively removed by adjusting the mass ratio of the second impurity ion to the second impurity ion. If a lower content of the second impurity ion is used, the concentration of the second impurity ion in the lithium sulfate back-extraction solution cannot be significantly reduced; if a higher content of the second impurity ion is used, other impurity ions are easily introduced, thereby affecting the purity of the lithium-containing product.

[0033] Preferably, in step S1, the pH value of the mixed solution is adjusted to 4-6 for the first time. For example, it can be 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, or 6, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable. This invention takes into account that when the lithium ion concentration is high, directly adjusting the pH value of the mixed solution to above 11 easily leads to the formation of lithium hydroxide precipitate, thereby exacerbating the loss of lithium elements in the solution. Therefore, the pH value of the mixed solution is adjusted to acidic for the first time.

[0034] Preferably, in step S1, the temperature of the first reaction is 20℃-40℃, for example, it can be 20℃, 25℃, 30℃, 35℃ or 40℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] In this invention, by adjusting the pH value of the mixed solution and the temperature of the first reaction to a lower value, it is beneficial to form calcium oxalate precipitate and avoid increasing the solubility of calcium oxalate under high temperature and high pH conditions.

[0036] Preferably, in step S1, the time for the first reaction is 0.5h-3h, for example, it can be 0.5h, 1h, 1.5h, 2h, 2.5h or 3h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] Preferably, in step S2, the pH value of the first filtrate is adjusted to ≥11 for the second time. For example, it can be 11, 11.5, 12, 12.5, 13, or 14, etc., and is not limited to the listed values; other unlisted values ​​within this range are also applicable. This invention, by adjusting the pH value of the first filtrate to ≥11, is more conducive to the precipitation of magnesium ions. The specific reaction principle is as follows:

[0038] Mg 2+ +2OH - =Mg(OH)2↓.

[0039] Preferably, in step S2, the temperature of the second reaction is 20℃-30℃, for example, it can be 20℃, 22℃, 25℃, 28℃ or 30℃, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0040] Preferably, in step S2, the time for the second reaction is 0.5h-2h, for example, it can be 0.5h, 0.8h, 1h, 1.5h or 2h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0041] Preferably, in step S3, further processing of the second filtrate includes: passing the second filtrate through a resin to remove impurities, thereby obtaining a purified lithium sulfate solution.

[0042] Preferably, the resin comprises a calcium-magnesium removal resin. The calcium-magnesium removal resin exemplary includes at least one of commercially available chelating resins or ion exchange resins.

[0043] Preferably, the flow rate of the second filtrate is ≤10 BV / h, for example, it can be 1 BV / h, 2 BV / h, 5 BV / h, 8 BV / h or 10 BV / h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0044] This invention further removes impurities by passing the second filtrate through a calcium and magnesium removal resin. This is because chemical precipitation cannot completely remove calcium and magnesium impurities from the lithium sulfate back-extraction solution, and the concentration of calcium and magnesium ions in the solution is difficult to reduce to below 1 mg / L. Therefore, this invention employs a combined process of chemical precipitation and resin removal, which can significantly reduce the concentration of divalent cation impurities in the solution, ensuring that the impurity content of the purified solution meets the feed requirements for preparing lithium-containing products using the bipolar membrane electrodialysis method.

[0045] Preferably, in the purified lithium sulfate solution, the concentrations of the first impurity ion, the second impurity ion, and the third impurity ion are each independently less than 1 mg / L, for example, 0.1 mg / L, 0.2 mg / L, 0.5 mg / L, 0.8 mg / L, or 0.95 mg / L, etc., and are not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0046] In a second aspect, the present invention provides a lithium sulfate solution, which is prepared by the method for removing impurities from lithium sulfate back-extraction solution as described in the first aspect.

[0047] Thirdly, the present invention provides a lithium-containing compound, which is prepared from a lithium sulfate solution as described in the second aspect.

[0048] In this invention, the lithium-containing compound includes at least one of lithium hydroxide or lithium carbonate, which has high purity.

[0049] Fourthly, the present invention provides an application of the lithium-containing compound as described in the third aspect, wherein the lithium-containing compound is used in the preparation of electrode materials.

[0050] In this invention, the lithium-containing compound can be used, for example, in the preparation of cathode materials, and this invention does not limit this use.

[0051] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] This invention provides a method for removing impurities from lithium sulfate back-extraction solution. First, a combination of a first impurity remover and a second impurity remover is used to remove copper ions, iron ions, and most of the calcium ions in the solution. Then, the pH value of the first filtrate is further adjusted to alkalinity to remove most of the magnesium ions in the solution. Finally, a further impurity removal process is combined to solve the technical problem of the difficulty in deeply removing divalent cation impurities such as copper, iron, calcium, and magnesium from lithium sulfate back-extraction solution.

[0054] Furthermore, the concentration of divalent cations such as copper, iron, calcium, and magnesium in the purified lithium sulfate solution of this invention can be reduced to below 1 mg / L, thus meeting the feed requirements for the preparation of high-purity lithium-containing products by bipolar membrane systems. Attached Figure Description

[0055] Figure 1 This is a flowchart of the method for removing impurities from lithium sulfate back-extraction solution provided by the present invention. Detailed Implementation

[0056] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be considered as specific limitations thereof.

[0057] Example 1

[0058] This embodiment provides a method for removing impurities from lithium sulfate back-extraction solution and the purified lithium sulfate solution, such as... Figure 1 As shown, the impurity removal method includes the following steps:

[0059] S1. Provide a lithium sulfate back-extraction solution, the composition of which is: Li + 21.83 g / L, impurity ions include: Cu 2+ 498.3 mg / L, Fe 2+ 16.6 mg / L, Ca 2+ 316.6 mg / L and Mg 2+ The concentration was 232.9 mg / L, and the pH value of the lithium sulfate back-extraction solution was 0.8.

[0060] 2g of sodium sulfide and 2g of oxalic acid were added to 1L of lithium sulfate back-extraction solution, and the pH of the mixture was adjusted to 4 with lithium hydroxide solution. The mixture was stirred and reacted at 20℃ for 0.5h. After the reaction was completed, the mixture was filtered to obtain the first residue and the first filtrate. The content of impurity ions in the first filtrate was determined to be Cu 2+ 1.3 mg / L, Fe 2+ 0.1 mg / L, Ca 2+ 15.5 mg / L and Mg 2+ 218.6 mg / L.

[0061] S2. Adjust the pH of the first filtrate obtained in step S1 to 11, stir the reaction at 20℃ for 0.5 h, and filter to obtain the second residue and the second filtrate after the reaction is complete; determine the content of impurity ions in the second filtrate, which are Cu 2+ 0.3 mg / L, Fe 2+ 0.05 mg / L, Ca 2+ 9.5 mg / L and Mg 2+ 5.1 mg / L.

[0062] S3. Pass the second filtrate obtained in step (2) through an ion exchange resin at a flow rate of 8 BV / h to obtain a purified lithium sulfate solution; determine the content of impurity ions in the purified lithium sulfate solution, which are Cu 2+ 0.1 mg / L, Fe 2+ 0.04 mg / L, Ca 2+ 0.7 mg / L and Mg 2+ 0.1 mg / L.

[0063] Example 2

[0064] This embodiment provides a method for removing impurities from lithium sulfate back-extraction solution and a purified lithium sulfate solution thereof. The impurity removal method includes the following steps:

[0065] S1. Provide a lithium sulfate back-extraction solution, the composition of which is: Li + 17.3 g / L, impurity ions include: Cu 2+ 46.4 mg / L, Fe 2+ 9.2 mg / L, Ca 2+ 172.1 mg / L and Mg 2+ The concentration was 65.2 mg / L, and the pH of the lithium sulfate back-extraction solution was 1.5.

[0066] 1g of sodium sulfide and 2g of oxalic acid were added to 2L of lithium sulfate back-extraction solution, and the pH of the mixed solution was adjusted to 5 with lithium hydroxide solution. The mixture was stirred and reacted at 30℃ for 1 hour. After the reaction was completed, the mixture was filtered to obtain the first filter residue and the first filtrate. The content of impurity ions in the first filtrate was determined to be Cu 2+ 0.3 mg / L, Fe 2+ 0.1 mg / L, Ca 2+ 9.8 mg / L and Mg 2+ 46.4 mg / L.

[0067] S2. Adjust the pH of the first filtrate obtained in step S1 to 12, stir the reaction, maintain the reaction temperature at 30℃ for 2 hours, and filter to obtain the second residue and the second filtrate after the reaction is complete; determine the content of impurity ions in the second filtrate, which are Cu 2+ 0.1 mg / L, Fe 2+ 0.06 mg / L, Ca 2+ 6.6 mg / L and Mg 2+ 1.6 mg / L.

[0068] S3. Pass the second filtrate obtained in step (2) through an ion exchange resin at a flow rate of 5 BV / h to obtain a purified lithium sulfate solution; determine the content of impurity ions in the purified lithium sulfate solution, which are Cu 2+ 0.08 mg / L, Fe 2+ 0.02 mg / L, Ca 2+ 0.3 mg / L and Mg 2+ 0.06 mg / L.

[0069] Example 3

[0070] This embodiment provides a method for removing impurities from lithium sulfate back-extraction solution and a purified lithium sulfate solution thereof. The impurity removal method includes the following steps:

[0071] S1. Provide a lithium sulfate back-extraction solution, the composition of which is: Li + 5.8 g / L, impurity ions include: Cu 2+ 346.6 mg / L, Fe 2+ 33.7 mg / L, Ca 2+ 338.3 mg / L and Mg 2+ The concentration was 353.6 mg / L, and the pH value of the lithium sulfate back-extraction solution was 1.8.

[0072] 3.5 g of sodium sulfide and 3 g of oxalic acid were added to 1 L of lithium sulfate back-extraction solution, and the pH of the mixed solution was adjusted to 5 with lithium hydroxide solution. The mixture was stirred and reacted at 30 °C for 2 h. After the reaction was completed, the mixture was filtered to obtain the first residue and the first filtrate. The content of impurity ions in the first filtrate was determined to be Cu 2+ 0.8 mg / L, Fe 2+ 0.14 mg / L, Ca 2+ 19.4 mg / L and Mg 2+ 328.6 mg / L.

[0073] S2. Adjust the pH of the first filtrate obtained in step S1 to 13, stir the reaction, maintain the reaction temperature at 30℃ for 2 hours, and filter to obtain the second residue and the second filtrate after the reaction is complete; determine the content of impurity ions in the second filtrate, which are Cu 2+ 0.07 mg / L, Fe 2+ 0.02 mg / L, Ca 2+ 11.6 mg / L and Mg 2+ 0.9 mg / L.

[0074] S3. Pass the second filtrate obtained in step (2) through an ion exchange resin at a flow rate of 3 BV / h to obtain a purified lithium sulfate solution; determine the content of impurity ions in the purified lithium sulfate solution, which are Cu 2+ 0.01 mg / L, Fe 2+ 0.01 mg / L, Ca 2+ 0.5 mg / L and Mg 2+ 0.03 mg / L.

[0075] Example 4

[0076] The difference between this embodiment and Embodiment 1 is that, in step S1, 0.51g of sodium sulfide and 2g of oxalic acid are added to 1L of lithium sulfate back-extraction solution, and the content of impurity ions in the purified lithium sulfate solution is measured to be Cu. 2+ 0.25 mg / L, Fe 2+ 0.32 mg / L, Ca 2+ 0.66 mg / L and Mg 2+ 0.1 mg / L, all other parameters are the same as in Example 1.

[0077] Example 5

[0078] The difference between this embodiment and Embodiment 1 is that, in step S1, 2g of sodium sulfide and 0.63g of oxalic acid are added to 1L of lithium sulfate back-extraction solution, and the content of impurity ions in the purified lithium sulfate solution is measured to be Cu. 2+ 0.1 mg / L, Fe 2+0.06 mg / L, Ca 2+ 0.95 mg / L and Mg 2+ 0.1 mg / L, all other parameters are the same as in Example 1.

[0079] Example 6

[0080] The difference between this embodiment and Embodiment 1 is that, in step S1, the pH value of the mixed solution is adjusted to 10 using lithium hydroxide solution, and the content of impurity ions in the purified lithium sulfate solution is measured to be Cu. 2+ 0.2 mg / L, Fe 2+ 0.1 mg / L, Ca 2+ 0.58 mg / L and Mg 2+ The concentration was 0.08 mg / L, which accelerated the loss of lithium. Everything else was the same as in Example 1.

[0081] Example 7

[0082] The difference between this embodiment and Embodiment 1 is that, in step S1, the reaction temperature is 60°C, and the content of impurity ions in the purified lithium sulfate solution is measured to be Cu. 2+ 0.2 mg / L, Fe 2+ 0.1 mg / L, Ca 2+ 0.81 mg / L and Mg 2+ 0.2 mg / L, all other parameters are the same as in Example 1.

[0083] Comparative Example 1

[0084] The difference between this comparative example and Example 1 is that in step S1, sodium sulfide is replaced with an equal mass of iron powder, and the content of impurity ions in the purified lithium sulfate solution is measured to be Cu. 2+ 0.15 mg / L, Fe 2+ 0.89 mg / L, Ca 2+ 0.48 mg / L and Mg 2+ 0.1 mg / L, all other parameters are the same as in Example 1.

[0085] Comparative Example 2

[0086] The difference between this comparative example and Example 1 is that, in step S1, oxalic acid is replaced with an equal mass of sodium carbonate, and the content of impurity ions in the purified lithium sulfate solution is measured to be Cu. 2+ 0.1 mg / L, Fe 2+ 0.06 mg / L, Ca 2+ 0.88 mg / L and Mg 2+ 0.1 mg / L, all other parameters are the same as in Example 1.

[0087] In summary, the lithium sulfate back-extraction solution purification method provided by this invention can significantly reduce the concentration of divalent cation impurities such as copper, iron, calcium, and magnesium in the lithium sulfate back-extraction solution, with almost no loss of lithium ions and no additional introduction of other impurity ions. This allows the purified lithium sulfate solution to meet the process requirements for preparing lithium-containing products using a bipolar membrane system. Furthermore, the process is low-cost, mild, and simple to operate, and can be applied to the conversion and preparation of products such as lithium carbonate and lithium hydroxide, with a wide range of applications.

[0088] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for removing impurities from lithium sulfate back-extraction solution, characterized in that, The method includes the following steps: S1. A mixed solution is obtained by mixing lithium sulfate back-extraction solution, a first impurity remover, and a second impurity remover; the pH of the mixed solution is adjusted to acidic for the first time, and a first filtrate and a first filter residue are obtained after the first reaction, wherein the first impurity remover includes a sulfiding agent, and the second impurity remover includes a calcium removal agent; the sulfiding agent includes sodium sulfide; the calcium removal agent includes oxalic acid and / or oxalate; the lithium sulfate back-extraction solution includes a first impurity ion, a second impurity ion, and a third impurity ion; the first impurity ion includes copper ions and iron ions; the second impurity ion includes calcium ions; and the third impurity ion includes magnesium ions; S2. Adjust the pH of the first filtrate to alkaline for the second time, and obtain the second filtrate and the second filter residue after the second reaction; S3. Further processing of the second filtrate includes: passing the second filtrate through a resin to remove impurities, thereby obtaining a purified lithium sulfate solution; wherein the concentrations of the first impurity ion, the second impurity ion, and the third impurity ion in the purified lithium sulfate solution are each independently less than 0.8 mg / L.

2. The method according to claim 1, characterized in that, In step S1, the concentrations of copper ions and iron ions in the lithium sulfate back-extraction solution are each independently less than 500 mg / L.

3. The method according to claim 1, characterized in that, In step S1, the concentrations of calcium ions and magnesium ions in the lithium sulfate back-extraction solution are each independently less than 500 mg / L.

4. The method according to claim 1, characterized in that, In step S1, the lithium sulfate back-extraction solution also includes lithium ions.

5. The method according to claim 4, characterized in that, In step S1, the concentration of lithium ions in the lithium sulfate back-extraction solution is ≥5 g / L.

6. The method according to claim 1, characterized in that, In step S1, the pH value of the lithium sulfate back-extraction solution is ≤2.

7. The method according to claim 1, characterized in that, In step S1, the mass ratio of the first impurity remover to the first impurity ion is (2-18):

1.

8. The method according to claim 1, characterized in that, In step S1, the calcium removal agent is oxalic acid.

9. The method according to claim 1, characterized in that, In step S1, the oxalate includes sodium oxalate and / or lithium oxalate.

10. The method according to claim 1, characterized in that, In step S1, the mass ratio of the second impurity remover to the second impurity ion is (4-12):

1.

11. The method according to claim 1, characterized in that, In step S1, the pH of the mixed solution is adjusted to 4-6 for the first time.

12. The method according to claim 1, characterized in that, In step S1, the temperature of the first reaction is 20℃-40℃.

13. The method according to claim 1, characterized in that, In step S1, the time for the first reaction is 0.5h-3h.

14. The method according to claim 1, characterized in that, In step S2, the pH value of the first filtrate is adjusted to ≥11 for the second time.

15. The method according to claim 1, characterized in that, In step S2, the temperature of the second reaction is 20℃-30℃.

16. The method according to claim 1, characterized in that, In step S2, the second reaction takes 0.5h-2h.

17. The method according to claim 1, characterized in that, In step S3, the resin includes a calcium-magnesium resin.

18. The method according to claim 1, characterized in that, In step S3, the flow rate of the second filtrate is ≤10 BV / h.

19. A lithium sulfate solution, characterized in that, The lithium sulfate solution is prepared by removing impurities from the lithium sulfate back-extraction solution as described in any one of claims 1-18.

20. A lithium-containing compound, characterized in that, The lithium-containing compound is prepared from the lithium sulfate solution as described in claim 19.

21. An application of the lithium-containing compound as described in claim 20, characterized in that, The lithium-containing compound is used in the preparation of electrode materials.

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