Impurity removal method of lithium sulfate slurry

Abstract

The invention provides an impurity removal method for lithium sulfate slurry, and relates to the technical field of lithium salt purification. The impurity removal method comprises the following steps: mixing lithium sulfate slurry with calcium carbonate to form first to-be-reacted slurry; after the first to-be-reacted slurry is subjected to first precipitation, a first mixture is obtained; performing first solid-liquid separation on the first mixture to obtain a first filtrate and a first precipitate; mixing the first filtrate with a pH regulator, and carrying out second precipitation to obtain a second mixture; performing second solid-liquid separation on the second mixture to obtain a second filtrate and a second precipitate; wherein the pH value of the second mixture is 6-10; mixing the second filtrate, a sodium hydroxide solution and sodium carbonate to form third to-be-reacted slurry; performing third precipitation on the third to-be-reacted slurry to obtain a third mixture; and carrying out third solid-liquid separation on the third mixture to obtain a lithium sulfate refined solution and a third precipitate. According to the method, the zinc impurity in the lithium sulfate slurry can be effectively removed, and the purity of the lithium sulfate product is improved.

Description

Technical Field

[0001] This application belongs to the technical field of lithium salt purification. Specifically, it relates to a method for removing impurities from lithium sulfate slurry. Background Art

[0002] As an important component of lithium battery materials, the quality of lithium sulfate directly affects the performance of the battery. The production technology of high-purity lithium sulfate is one of the most concerned hot issues in the lithium battery industry. At present, the production of lithium sulfate mainly adopts the wet process. The production process of lithium sulfate includes: first, the preparation of crude lithium sulfate, where lithium ore is subjected to high-temperature roasting and acidified roasting to obtain a crude lithium sulfate solution, and then leaching to obtain an acidified material; second, the refining of lithium sulfate, that is, water leaching, filtration, and impurity removal of the acidified material to obtain a refined lithium sulfate solution. During the production process of lithium sulfate, the main impurities are calcium, magnesium, aluminum, iron, zinc, etc. At present, most of the aluminum and iron in the solution are removed mainly through the neutralization leaching method. Calcium and magnesium in the solution need to be further removed by adding liquid caustic soda and soda ash. However, in the actual production process, the zinc content in the refined lithium sulfate solution obtained after removing calcium and magnesium exceeds the standard, affecting the purity of lithium sulfate. Summary of the Invention

[0003] The main purpose of this application is to provide a method for removing impurities from lithium sulfate slurry to solve the problem of high zinc element content in lithium sulfate slurry in the prior art.

[0004] To achieve the above purpose, on the one hand, this application provides a method for removing impurities from lithium sulfate slurry, including:

[0005] S1, mixing the lithium sulfate slurry with calcium carbonate to form a first reaction slurry to be; after the first precipitation of the first reaction slurry to be, a first mixture is obtained; the first mixture is subjected to first solid-liquid separation to obtain a first filtrate and a first precipitate;

[0006] S2, mixing the first filtrate with a pH regulator to form a second reaction slurry to be; after the second precipitation of the second reaction slurry to be, a second mixture is obtained; the second mixture is subjected to second solid-liquid separation to obtain a second filtrate and a second precipitate; wherein, the pH value of the second mixture is 6 - 10;

[0007] S3, mixing the second filtrate, sodium hydroxide solution and sodium carbonate to form a third reaction slurry to be; after the third precipitation of the third reaction slurry to be, a third mixture is obtained; the third mixture is subjected to third solid-liquid separation to obtain a refined lithium sulfate solution and a third precipitate.

[0008] Further, the pH regulator includes sodium hydroxide and / or the third precipitate.

[0009] Preferably, mix the third precipitate with water to form a calcium- and magnesium-removing slurry; return the calcium- and magnesium-removing slurry to S2 to mix with the first filtrate to form an intermediate mixture; mix the intermediate mixture with a sodium hydroxide solution to form a second slurry to be reacted.

[0010] Further, the pH value of the second mixture is 7.5 - 10.

[0011] Further, the pH value of the first mixture < 6; and / or,

[0012] the pH value of the third mixture > 10.

[0013] Further, the pH value of the first mixture is 3.5 - 5.5; and / or,

[0014] the pH value of the third mixture is 10.5 - 13.

[0015] Further, S1 includes: mixing a lithium sulfate slurry with a calcium carbonate slurry to form a first slurry to be reacted; wherein, the volume ratio of the lithium sulfate slurry to the calcium carbonate slurry is (7.5 - 9):1, the density of the lithium sulfate slurry is 1 g / cm 3 ~1.4 g / cm 3 , and the mass concentration of calcium carbonate in the calcium carbonate slurry is 1.2 g / cm 3 ~1.3 g / cm 3 .

[0016] Further, the volume ratio of the second filtrate to the sodium hydroxide solution is 100:(0.2 - 2.0), and the mass concentration of the sodium hydroxide solution is 40 - 60%; and / or,

[0017] the mass of sodium carbonate is 2 - 10 times the mass of calcium in the lithium sulfate slurry.

[0018] Further, the temperature of the first precipitation is 25°C - 60°C, and the time of the first precipitation is 1 h - 6 h; and / or,

[0019] the temperature of the second precipitation is 50°C - 90°C, and the time of the second precipitation is 1 h - 3 h; and / or,

[0020] the temperature of the third precipitation is 50°C - 90°C, and the time of the second precipitation is 1 h - 3 h.

[0021] Further,

[0022] the pH value of the lithium sulfate slurry is 0.5 - 2.5; and / or,

[0023] the temperature of the lithium sulfate slurry is 25°C - 60°C.

[0024] Further, the concentration of Li2O in the lithium sulfate slurry is 10 g / L to 15 g / L, the concentration of Fe element is 2000 mg / L to 3000 mg / L, the concentration of Al element is 2000 mg / L to 3000 mg / L, the concentration of Zn element is 20 mg / L to 30 mg / L, the concentration of Ca element is 500 mg / L to 900 mg / L, and the concentration of Mg element is 400 mg / L to 600 mg / L.

[0025] Applying the technical solution of the present application, most of the aluminum and iron in the slurry are neutralized by calcium carbonate. By precisely controlling the pH value to be 6 to 10, the precipitation formation of Zn(OH)2 is effectively promoted, avoiding the problem of zinc element redissolution caused by a large pH when directly removing calcium and magnesium in the slurry with liquid alkali and soda ash. Due to the use of precise pH value control, the removal effect of zinc is more stable, effectively removing zinc impurities in the lithium sulfate slurry and improving the purity of the lithium sulfate product. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The specification drawings forming a part of the present application are used to provide a further understanding of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation of the present application. In the drawings:

[0027] Figure 1 is the process flow diagram of the impurity removal method for the lithium sulfate slurry in an embodiment of the present application;

[0028] Figure 2 is the distribution of stable species of Zn(II) in different pH ranges under the temperature condition of 40°C;

[0029] Figure 3 is the distribution of stable species of Zn(II) in different pH ranges under the temperature condition of 90°C. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present application will be described in detail below with reference to the embodiments.

[0031] As described in the background art, there is a problem that zinc elements in the existing lithium sulfate slurry are difficult to remove. To solve the above technical problems, as Figure 1 shown, the present application provides an impurity removal method for a lithium sulfate slurry, including:

[0032] S1, mixing the lithium sulfate slurry with calcium carbonate to form a first slurry to be reacted; after the first slurry to be reacted undergoes a first precipitation, a first mixture is obtained; the first mixture is subjected to a first solid-liquid separation to obtain a first filtrate and a first precipitate;

[0033] S2. Mix the first filtrate with a pH regulator to form a second reaction slurry to be processed. After the second precipitation of the second reaction slurry to be processed, a second mixture is obtained. Perform second solid-liquid separation on the second mixture to obtain a second filtrate and a second precipitate. Among them, the pH value of the second mixture is 6-10.

[0034] S3. Mix the second filtrate, sodium hydroxide solution and sodium carbonate to form a third reaction slurry to be processed. After the third precipitation of the third reaction slurry to be processed, a third mixture is obtained. Perform third solid-liquid separation on the third mixture to obtain a refined lithium sulfate solution and a third precipitate.

[0035] In step S1, mix the lithium sulfate slurry with calcium carbonate (which can also be called limestone), and use calcium carbonate to adjust the pH value to a suitable weak acidity, so that metal ions such as iron and aluminum react with calcium carbonate to form water-insoluble precipitates, and a first mixture is obtained. After the first solid-liquid separation of the first mixture, a first filtrate and a first precipitate are obtained. Among them, iron and aluminum in the first filtrate have been removed, while the first precipitate contains precipitates formed by these metal ions such as iron and aluminum.

[0036] In step S2, use a pH regulator to adjust the pH value of the first filtrate to neutral to weak alkaline. After the second precipitation, a second mixture is obtained. The pH value of the second mixture is 6-10. This specific pH range is conducive to the formation of Zn(OH)2 precipitate, thereby effectively removing zinc ions. Compared with the impurity removal method that only neutralizes with calcium carbonate, this step ensures the full precipitation and removal of zinc ions through precise pH control, ensuring the quality of the final product. After the second solid-liquid separation of the second mixture, a second filtrate and a second precipitate are obtained. Among them, Zn in the second filtrate has been removed, while the second precipitate contains precipitates formed by Zn.

[0037] In step S3, sodium hydroxide can further adjust the pH value to enhance the alkalinity of the second filtrate, prompting impurities that are not easily precipitated in a neutral to weak alkaline environment to form precipitates, such as magnesium ions. The addition of sodium carbonate can target specific ions, such as calcium ions. Calcium ions in the second filtrate react with CO3 2- to form a more stable CaCO3 precipitate, obtaining a third mixture. After the third solid-liquid separation of the third mixture, a refined lithium sulfate solution with higher purity and a third precipitate are obtained. The third precipitate contains precipitates formed by calcium and magnesium.

[0038] Compared with the traditional impurity removal process where calcium carbonate is used for neutralization and then liquid caustic soda and soda ash are directly used for further impurity removal, in this application, by adding a weak alkaline pH adjustment process, the precipitation formation of Zn(OH)₂ is effectively promoted, avoiding the problem of zinc element redissolution caused by a large pH value when directly implementing step S3. Secondly, in this application, by precisely controlling the pH value to be 6 - 10, the precipitation formation of Zn(OH)₂ is effectively promoted, and impurity removal is carried out within a relatively narrow pH range to ensure the full precipitation of zinc ions. Due to the use of precise pH control, the removal effect of zinc is more stable, effectively removing zinc impurities in the lithium sulfate slurry. In addition, in this application, by first removing iron and aluminum, then removing zinc, and finally removing calcium and magnesium, in the process of such step-by-step impurity removal, the possible mutual influence between impurities such as iron, aluminum, calcium, magnesium, and zinc is avoided, further improving the impurity removal efficiency, making the impurity removal process more efficient, improving the purity of the lithium sulfate product, and resulting in a lower impurity content and higher purity in the refined lithium sulfate solution.

[0039] The first solid-liquid separation, the second solid-liquid separation, and the third solid-liquid separation can use filtration and plate-and-frame filter presses to achieve solid-liquid separation, more thoroughly removing solid impurities in the slurry, ensuring the purity of the filtrate, and providing high-quality raw materials for the subsequent lithium salt purification process.

[0040] In some embodiments, the pH regulator includes sodium hydroxide and / or a third precipitate. The third precipitate is actually the calcium and magnesium removal residue, which has a relatively high alkalinity. Using the third precipitate as the pH regulator and returning it to S2 can increase the pH of the first filtrate, reduce the consumption of liquid caustic soda while improving the solid-liquid separation effect, and at the same time realize the high-value utilization of the calcium and magnesium removal residue.

[0041] In the specific implementation process of the present invention, the pH regulator can be mixed with the first filtrate in the form of a solution. For example, in some embodiments, the third precipitate is mixed with water to form a calcium and magnesium removal slurry; the calcium and magnesium removal slurry is returned to S2 and mixed with the first filtrate to form an intermediate mixture; the intermediate mixture is mixed with a sodium hydroxide solution to form a second reaction-ready slurry.

[0042] In order to further improve the precipitation efficiency of zinc elements, in some embodiments, the pH value of the second mixture is 7.5 - 10, such as 7.5, 8, 8.5, 9, 9.5, 10 or any range composed of any two of them.

[0043] In some embodiments, the pH value of the first mixture < 6. Under this acidic condition, the dissolution and precipitation separation of aluminum and iron can be effectively promoted. Since these metals such as aluminum and iron are more inclined to form insoluble hydroxides at a lower pH value, by controlling the pH value in the acidic range, it helps to preliminarily remove impurities such as aluminum and iron, and can prompt them to precipitate, so as to be removed in the subsequent solid-liquid separation.

[0044] In some embodiments, the pH value of the third mixture is > 10. In a strongly alkaline environment, it can promote the formation of stable carbonate precipitates of hardness ions such as calcium and magnesium. When the pH value rises to the strongly alkaline range, calcium and magnesium ions in the solution can react with carbonate or hydroxide ions to form water-insoluble calcium carbonate and magnesium hydroxide precipitates, which can be effectively removed during solid-liquid separation processes such as filtration.

[0045] The present invention does not limit the specific pH values of the first mixture and the third mixture, as long as the above requirements are met. In some embodiments, the pH value of the first mixture is 3.5 - 5.5. By controlling the pH value of the first mixture, it can also be understood that controlling the reaction end-point pH value of the first precipitate to be 3.5 - 5.5 can optimize the precipitation process, improve the removal efficiency of iron and aluminum, while avoiding the use of excessive precipitants and reducing costs.

[0046] In some embodiments, the pH value of the third mixture is 10.5 - 13. By controlling the pH value of the third mixture, it can also be understood that controlling the reaction end-point pH value of the third precipitate to be 10.5 - 13 can optimize the precipitation process, improve the removal efficiency of calcium and magnesium, while avoiding the use of excessive precipitants and reducing costs. By precisely controlling the pH value, the loss of lithium ions can be avoided during the process of removing impurities.

[0047] In some embodiments, S1 includes: mixing a lithium sulfate slurry with a calcium carbonate slurry to form a first slurry to be reacted; wherein, the volume ratio of the lithium sulfate slurry to the calcium carbonate slurry is (7.5 - 9):1, the density of the lithium sulfate slurry is 1 g / cm 3 ~1.4 g / cm 3 and the mass concentration of calcium carbonate in the calcium carbonate slurry is 1.2 g / cm 3 ~1.3 g / cm 3 . By reasonably controlling the dosage of calcium carbonate, the best aluminum and iron removal effect can be achieved while minimizing the impact on the removal processes of other impurities.

[0048] In the specific implementation process of the present application, calcium carbonate can be first mixed with water to form a calcium carbonate slurry, and then the lithium sulfate slurry is mixed with the calcium carbonate slurry. The fineness of calcium carbonate in the calcium carbonate slurry is usually relatively high, which can increase its dispersibility in the solution and make the reaction more uniform and thorough.

[0049] In some embodiments, the volume ratio of the second filtrate to the sodium hydroxide solution is 100:(0.2 - 2), such as 100:0.2, 100:0.5, 100:1, 100:2, or the range composed of any two of them. The mass concentration of the sodium hydroxide solution is 40 - 60%, such as 40%, 45%, 50%, 55%, 60%, or the range composed of any two of them. In some embodiments, the mass of sodium carbonate is 2 - 10 times the mass of calcium element in the lithium sulfate slurry. By controlling the addition amounts of the sodium hydroxide solution and sodium carbonate, the maximum removal of calcium and magnesium can be achieved.

[0050] In some embodiments, the temperature of the first precipitation is 25°C - 60°C, and the time of the first precipitation is 1h - 6h. Within this temperature range, the solubility of calcium carbonate is relatively low, and it can be used as an alkaline substance to neutralize the acidic substances in the slurry, thereby increasing the pH value of the solution, ensuring that the first precipitation can proceed fully, and enabling the more effective removal of iron and aluminum.

[0051] In some embodiments, the temperature of the second precipitation is 50°C - 90°C, and the time of the second precipitation is 1h - 3h. By controlling the temperature and time of the second precipitation, the impurity removal reaction becomes more complete, and the generated precipitate is more easily filtered and separated, thereby improving the efficiency of solid-liquid separation. This not only accelerates the process flow but also reduces the soluble residues in the filter residue and improves the purity of the filtrate.

[0052] In some embodiments, the temperature of the third precipitation is 50°C - 90°C, and the time of the third precipitation is 1h - 3h. This reaction condition optimizes the third precipitation process, enabling the more effective removal of calcium and magnesium while ensuring the recovery rate of lithium ions.

[0053] Among them, the lithium sulfate slurry can be formed by mixing acidified materials with water. The density of the lithium sulfate slurry is 1 g / cm 3 ~1.4 g / cm 3 , such as 1 g / cm 3 , 1.1 g / cm 3 , 1.15 g / cm 3 , 1.2 g / cm 3 , 1.25 g / cm 3 , 1.3 g / cm 3 , 1.4 g / cm 3 or the range composed of any two of them.

[0054] The lithium sulfate slurry of the present application can be obtained by subjecting lithium-containing ore to high-temperature roasting, acid roasting, and water leaching in sequence. The lithium sulfate slurry contains various impurity ions, such as Fe, Al, Zn, Ca, Mg, etc. The present application does not limit the specific type of the lithium sulfate slurry. For example, in some embodiments, the pH value of the lithium sulfate slurry is 0.5 to 2.5, such as 0.5, 1, 1.5, 2, 2.5, or the range composed of any two of them.

[0055] In some embodiments, the temperature of the lithium sulfate slurry is 25°C to 60°C. By limiting the temperature of the lithium sulfate slurry, the formation of the first precipitate can be promoted.

[0056] In some embodiments, the concentration of Li2O in the lithium sulfate slurry is 10 g / L to 15 g / L, the concentration of Fe element is 2000 mg / L to 3000 mg / L, the concentration of Al element is 2000 mg / L to 3000 mg / L, the concentration of Zn element is 20 mg / L to 30 mg / L, the concentration of Ca element is 500 mg / L to 900 mg / L, and the concentration of Mg element is 400 mg / L to 600 mg / L. By the method provided by the present application, the lithium content can be significantly increased, the contents of Fe, Al, Ca, and Mg elements can be reduced, especially the content of Zn element can be reduced, and the utilization efficiency of lithium resources is effectively improved. The finally obtained refined lithium sulfate solution of the present application contains high-purity lithium sulfate and can be directly used for the production of lithium battery materials.

[0057] It should be noted that the present invention uses the concentration of lithium oxide to represent the content of lithium in the solution. In the specific implementation process of the present invention, it is necessary to convert the concentration of lithium oxide into the concentration of lithium sulfate.

[0058] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0059] Example 1

[0060] The density of the lithium sulfate slurry in this example is 1.28 g / cm 3 , the pH value is 1.5, in which the Li2O concentration is 10.84 g / L, the Zn element concentration is 20.75 mg / L, the Al element concentration is 2182.79 mg / L, the Fe element concentration is 2556.8 mg / L, the Ca element concentration is 670.56 mg / L, and the Mg element concentration is 464.62 mg / L.

[0061] The impurity removal method of the lithium sulfate slurry in this example includes the following steps:

[0062] S1, mixing the lithium sulfate slurry with calcium carbonate having a mass concentration of 1.3 g / cm 3Mix with the calcium carbonate slurry, react at a temperature of 40 °C for 1 h, control the pH value at the end of the reaction to be 5, and obtain the first mixture with a pH value of 5; subject the second mixture to solid-liquid separation through a plate-and-frame filter press to obtain the first filtrate and the first precipitate; the volume ratio of the lithium sulfate slurry to the calcium carbonate slurry is 8:1;

[0063] S2, Add the calcium and magnesium removal slurry with a pH value of about 11.5 to the first filtrate, then add sodium hydroxide solution, stir at 70 °C for 2 h, control the pH value at the end of the reaction to be 7.9, and obtain the second mixture with a pH value of 7.9; filter the second mixture through a funnel to obtain the second filtrate and the second precipitate;

[0064] S3, React the second filtrate, sodium hydroxide solution and sodium carbonate at a temperature of 80 °C for 4 h, control the pH value at the end of the reaction to be 12, and obtain the third mixture with a pH value of 12; subject the third mixture to solid-liquid separation through a plate-and-frame filter press to obtain the refined lithium sulfate solution and the third precipitate; the volume ratio of the added sodium hydroxide solution to the second filtrate is 0.6:100, the mass concentration of the sodium hydroxide solution is 50%, and the mass of sodium carbonate is 4 times the mass of calcium in the lithium sulfate slurry;

[0065] Mix the third precipitate with water to form a calcium and magnesium removal slurry with a pH value of 11.5; return the calcium and magnesium removal slurry to S2.

[0066] Example 2

[0067] The density of the lithium sulfate slurry in this example is 1.25 g / cm 3 , the pH value is 1.45, in which the Li2O concentration is 11.65 g / L, the Zn element concentration is 24.43 mg / L, the Al element concentration is 2042.34 mg / L, the Fe element concentration is 2457.39 mg / L, the Ca element concentration is 740.21 mg / L, and the Mg element concentration is 468.09 mg / L.

[0068] The impurity removal method of the lithium sulfate slurry in this example includes the following steps:

[0069] S1, Mix the lithium sulfate slurry with the calcium carbonate slurry with a mass concentration of 1.3 g / cm 3 , react at a temperature of 40 °C for 1 h, control the pH value at the end of the reaction to be 4.5, and obtain the first mixture with a pH value of 4.5; subject the second mixture to solid-liquid separation through a plate-and-frame filter press to obtain the first filtrate and the first precipitate; the volume ratio of the lithium sulfate slurry to the calcium carbonate slurry is 9:1;

[0070] S2. Add the calcium and magnesium removal slurry with a pH value of about 11.5 to the first filtrate, and then add sodium hydroxide solution. Stir at 70 °C for 2 h, and control the pH value at the end of the reaction to be 8.1 to obtain the second mixture with a pH value of 8.1. Filter the second mixture through a funnel to obtain the second filtrate and the second precipitate.

[0071] S3. React the second filtrate, sodium hydroxide solution and sodium carbonate at 80 °C for 4 h, and control the pH value at the end of the reaction to be 11.5 to obtain the third mixture with a pH value of 11.5. Perform solid-liquid separation on the third mixture through a plate and frame filter press to obtain the refined lithium sulfate solution and the third precipitate. The added volume of the sodium hydroxide solution is 0.9:100 of the volume of the second filtrate, the mass concentration of the sodium hydroxide solution is 50%, and the mass of the sodium carbonate is 6 times the mass of the calcium element in the lithium sulfate slurry.

[0072] Mix the third precipitate with water to form a calcium and magnesium removal slurry with a pH value of 11.5. Return the calcium and magnesium removal slurry to S2.

[0073] Example 3

[0074] In this example, the density of the lithium sulfate slurry is 1.3 g / cm 3 , the pH value is 1.4, the concentration of Li2O is 13.16 g / L, the concentration of Zn element is 26.43 mg / L, the concentration of Al element is 2032.10 mg / L, the concentration of Fe element is 2478.53 mg / L, the concentration of Ca element is 670.77 mg / L, and the concentration of Mg element is 566.75 mg / L.

[0075] The impurity removal method of the lithium sulfate slurry in this example includes the following steps:

[0076] S1. Mix the lithium sulfate slurry with the calcium carbonate slurry with a mass concentration of 1.3 g / cm 3 at 40 °C for 1 h, and control the pH value at the end of the reaction to be 5 to obtain the first mixture with a pH value of 5. Perform solid-liquid separation on the second mixture through a plate and frame filter press to obtain the first filtrate and the first precipitate. The volume ratio of the lithium sulfate slurry to the calcium carbonate slurry is 7.5:1.

[0077] S2. Add the calcium and magnesium removal slurry with a pH value of about 11.5 to the first filtrate, and then add sodium hydroxide solution to form the second slurry to be reacted. Stir at 70 °C for 2 h, and control the pH value at the end of the reaction to be 8 to obtain the second mixture with a pH value of 8. Filter the second mixture through a funnel to obtain the second filtrate and the second precipitate.

[0078] S3. React the second filtrate, sodium hydroxide solution and sodium carbonate at 80 °C for 4 h, control the pH value at the end point of the reaction to be 12.5 to obtain a third mixture with a pH value of 12.5; subject the third mixture to solid-liquid separation through a plate and frame filter press to obtain a refined lithium sulfate solution and a third precipitate; wherein the volume ratio of the sodium hydroxide solution to the second filtrate is 1.2:100, the mass concentration of the sodium hydroxide solution is 50%, and the mass of the sodium carbonate is 8 times the mass of calcium in the lithium sulfate slurry.

[0079] Mix the third precipitate with water to form a calcium and magnesium removal slurry with a pH value of 11.5; return the calcium and magnesium removal slurry to S2.

[0080] Example 4

[0081] The difference from Example 1 is that in S2, only sodium hydroxide solution is added to the first filtrate.

[0082] Example 5

[0083] The difference from Example 1 is that in S1, control the pH value at the end point of the reaction to be 3.5 to obtain a first mixture with a pH value of 3.5.

[0084] Example 6

[0085] The difference from Example 1 is that in S1, control the pH value at the end point of the reaction to be 5.5 to obtain a first mixture with a pH value of 5.5.

[0086] Example 7

[0087] The difference from Example 1 is that in S3, control the pH value at the end point of the reaction to be 10.5 to obtain a third mixture with a pH value of 10.5.

[0088] Example 8

[0089] The difference from Example 1 is that in S3, control the pH value at the end point of the reaction to be 13 to obtain a third mixture with a pH value of 13.

[0090] Comparative Example 1

[0091] The difference from Example 1 is that step S2 is omitted.

[0092] Use inductively coupled plasma optical emission spectrometry (ICP-OES) to detect the contents of Al, Fe, Zn, Ca, and Mg elements in the refined lithium sulfate solution finally formed in the examples and comparative examples, and the detection limit is at the ppm level.

[0093] The test results are shown in Table 1.

[0094] Table 1

[0095]

[0096] Compared with Comparative Example 1, in the Example, by adding a separate zinc removal process, the zinc content in the refined lithium sulfate solution is at a relatively low level, effectively preventing the phenomenon of zinc exceeding the standard. The Zn content in the refined lithium sulfate solution of Comparative Example 1 > 0.08 mg / L, and Zn cannot be effectively removed. Compared with Example 4, in Examples 1-3, the calcium and magnesium removal slag from the subsequent section is recycled into the zinc removal process of S2 to adjust the pH value, reducing the increase in caustic soda consumption. At the same time, the high-value utilization of the calcium and magnesium removal slag is realized, reducing the production cost.

[0097] Figure 2 and Figure 3 are the stable species distribution of Zn(II) in different pH ranges at 40 °C and 90 °C temperature conditions respectively. According to Figure 2 and Figure 3 it can be seen that based on the theoretical calculation results of the precipitation of Zn(OH)2 at different temperatures and pH values, it can be known from the theoretical calculation results that Zn(II) will form precipitates in the pH range of 6.5 - 12.

[0098] In Comparative Example 1, since the pH is relatively low during the first-stage addition of limestone for impurity removal and relatively high during the subsequent calcium and magnesium removal, finally, a part of Zn(II) may redissolve back into the solution. Therefore, the zinc element in the refined lithium sulfate solution of Comparative Example 1 exceeds the standard.

[0099] Furthermore, compared with Examples 5 and 7, in Examples 1-4, 6, and 8, by further adjusting the reaction end point pH value of each step, on the premise of ensuring that the Zn content ≤ 0.08 mg / L, the contents of Al, Fe, Ca, and Mg elements can be further reduced.

[0100] It should be noted that the terms "first", "second", etc. in the description and claims of this application are used to distinguish similar objects and do not necessarily need to describe a specific order or sequence. It should be understood that such terms can be interchanged under appropriate circumstances so that the embodiments of this application described here can be implemented in an order other than those described here.

[0101] The above are only the preferred embodiments of this application and are not used to limit this application. For those skilled in the art, this application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the protection scope of this application.

Claims

1. A method for removing impurities from a lithium sulfate slurry, characterized in that, Including: S1. Mix lithium sulfate slurry with calcium carbonate to form a first slurry to be reacted; after the first precipitation of the first slurry to be reacted, a first mixture is obtained; perform first solid-liquid separation on the first mixture to obtain a first filtrate and a first precipitate; S2. Mix the first filtrate with a pH regulator to form a second slurry to be reacted; after the second precipitation of the second slurry to be reacted, a second mixture is obtained; perform second solid-liquid separation on the second mixture to obtain a second filtrate and a second precipitate; wherein, the pH value of the second mixture is 6-10; S3. Mix the second filtrate, sodium hydroxide solution and sodium carbonate to form a third slurry to be reacted; after the third precipitation of the third slurry to be reacted, a third mixture is obtained; perform third solid-liquid separation on the third mixture to obtain a refined lithium sulfate solution and a third precipitate.

2. The impurity removal method according to claim 1, wherein, The pH regulator includes sodium hydroxide and / or the third precipitate; Preferably, mix the third precipitate with water to form a calcium and magnesium removal slurry; return the calcium and magnesium removal slurry to S2 to mix with the first filtrate to form an intermediate mixture; mix the intermediate mixture with a sodium hydroxide solution to form the second slurry to be reacted.

3. The impurity removal method according to claim 1 or 2, wherein The pH value of the second mixture is 7.5-10.

4. The impurity removal method according to claim 1 or 2, characterized in that, The pH value of the first mixture < 6; and / or, The pH value of the third mixture > 10.

5. The impurity removal method according to claim 4, wherein The pH value of the first mixture is 3.5-5.5; and / or, The pH value of the third mixture is 10.5-13.

6. The impurity removal method according to claim 1 or 2, characterized in that, S1 includes: Mix the lithium sulfate slurry with the calcium carbonate slurry to form a first slurry to be reacted; wherein, the volume ratio of the lithium sulfate slurry to the calcium carbonate slurry is (7.5 to 9):1, and the density of the lithium sulfate slurry is 1 g / cm 3 ~1.4 g / cm 3 , and the mass concentration of calcium carbonate in the calcium carbonate slurry is 1.2 g / cm 3 ~1.3 g / cm 3 .

7. The impurity removal method according to claim 6, wherein The volume ratio of the second filtrate to the sodium hydroxide solution is 100:(0.2-2.0), and the mass concentration of the sodium hydroxide solution is 40%-60%; and / or, The mass of the sodium carbonate is 2-10 times the mass of calcium element in the lithium sulfate slurry.

8. The impurity removal method according to claim 2, wherein The temperature of the first precipitation is 25°C-60°C, and the time of the first precipitation is 1h-6h; and / or, The temperature of the second precipitation is 50°C-90°C, and the time of the second precipitation is 1h-3h; and / or, The temperature of the third precipitation is 50°C-90°C, and the time of the second precipitation is 1h-3h.

9. The impurity removal method according to claim 1 or 2, characterized in that, The pH value of the lithium sulfate slurry is 0.5-2.5; and / or, The temperature of the lithium sulfate slurry is 25°C-60°C.

10. The impurity removal method according to claim 1 or 2, characterized in that, The concentration of Li2O in the lithium sulfate slurry is 10g / L-15g / L, the concentration of Fe element is 2000mg / L-3000mg / L, the concentration of Al element is 2000mg / L-3000mg / L, the concentration of Zn element is 20mg / L-30mg / L, the concentration of Ca element is 500mg / L-900mg / L, and the concentration of Mg element is 400mg / L-600mg / L.

Images