Preparation method of lithium carbonate and lithium carbonate

Abstract

The invention discloses a preparation method of lithium carbonate and the lithium carbonate. The preparation method of the lithium carbonate comprises the following steps: first lithium precipitation treatment: dropwise adding a first lithium sulfate solution into a first carbonate solution to form first mixed slurry; second lithium precipitation treatment: taking at least part of the first mixed slurry as return slurry, uniformly mixing the return slurry with a second carbonate solution to obtain second mixed slurry, dropwise adding a second lithium sulfate solution into the second mixed slurry to form third mixed slurry, and separating out crude lithium carbonate from at least part of the third mixed slurry; washing: washing the crude lithium carbonate to obtain the lithium carbonate. According to the preparation method of the lithium carbonate, the lithium carbonate in the return slurry can be used as the seed crystal, so that the lithium carbonate is precipitated on the surface of the lithium carbonate seed crystal in the subsequent lithium precipitation process, impurity residues are reduced, and the purity consistency of the lithium carbonate is relatively high. Meanwhile, the excess coefficient of carbonate in subsequent second lithium precipitation treatment is improved, the purity and the lithium precipitation rate are improved, and the cost is saved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium carbonate, and in particular to a preparation method of lithium carbonate and lithium carbonate. Background Art

[0002] With the development of new technologies, especially the increasing popularity of lithium metal polymer rechargeable batteries, lithium batteries for hybrid electric vehicles continue to replace nickel-metal hydride batteries, etc., and the global market demand for lithium compounds continues to grow. In the relevant technology, the parallel feeding production method is often used to produce lithium carbonate to meet the use of batteries. However, the lithium carbonate prepared by the above production method has serious polycrystal and / or peritectic problems, is difficult to wash, and is prone to residual impurities such as sulfate, resulting in a decrease in the purity of the prepared lithium carbonate. Summary of the invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, one object of the present invention is to provide a method for preparing lithium carbonate, which avoids the occurrence of polycrystals and / or peritectics, reduces residual impurities, facilitates the removal of impurities such as sulfate by washing, and makes the purity of lithium carbonate more consistent.

[0004] Another object of the present invention is to provide a lithium carbonate.

[0005] The method for preparing lithium carbonate according to the first embodiment of the present invention comprises the following steps: First lithium precipitation treatment: adding the first lithium sulfate solution dropwise into the first carbonate solution to form a first mixed slurry; Second lithium precipitation treatment: taking at least a portion of the first mixed slurry as a back slurry, mixing the back slurry with a second carbonate solution to form a second mixed slurry, adding a second lithium sulfate solution dropwise to the second mixed slurry to form a third mixed slurry, and taking at least a portion of the third mixed slurry to separate crude lithium carbonate; Washing: washing the crude lithium carbonate to obtain lithium carbonate.

[0006] According to the preparation method of lithium carbonate of the embodiment of the present invention, at least part of the first mixed slurry after the first lithium precipitation treatment is used as a back slurry, and the back slurry is mixed with the second carbonate solution and then the second lithium sulfate solution is added dropwise to prepare lithium carbonate. Thus, at least part of the first mixed slurry is used as a back slurry, which can ensure the stability of the continuous lithium precipitation process system, and the lithium carbonate in the back slurry can be used as a crystal seed, so that the subsequent lithium precipitation process is precipitated on the surface of the lithium carbonate seed, reducing nucleation, further avoiding the appearance of polycrystal and / or peritectic, reducing impurity residues, and facilitating the use of washing to remove impurities such as sulfate, so that the purity consistency of lithium carbonate is higher. At the same time, the excess carbonate in the back slurry can also be used to increase the excess coefficient of carbonate in the subsequent second lithium precipitation treatment, improve the purity and lithium precipitation rate, and save costs.

[0007] According to some embodiments of the present invention, at least one third lithium precipitation treatment is performed: taking at least a portion of the third mixed slurry as a back slurry, mixing the back slurry with a third carbonate solution, adding a third lithium sulfate solution to form a fourth mixed slurry, taking at least a portion of the fourth mixed slurry as a back slurry, and taking at least a portion of the fourth mixed slurry to separate crude lithium carbonate.

[0008] According to some embodiments of the present invention, the molar ratio of lithium sulfate in the first lithium sulfate solution to carbonate in the first carbonate solution is 1:(1-3); and / or the mass ratio of the second lithium sulfate solution or the third lithium sulfate solution to the back pulp is 1:(5-20).

[0009] According to some embodiments of the present invention, the lithium ion concentration in the first lithium sulfate solution, the second lithium sulfate solution and the third lithium sulfate solution is 20 g / L to 50 g / L; and / or the concentration of the first carbonate solution, the second carbonate solution and the third carbonate solution is 200 g / L to 300 g / L.

[0010] According to some embodiments of the present invention, the first carbonate solution, the second carbonate solution and the carbonate solution are independently selected from at least one of sodium carbonate, ammonium carbonate and potassium carbonate.

[0011] According to some embodiments of the present invention, the second lithium precipitation treatment further comprises: taking at least a portion of the first mixed slurry to separate crude lithium carbonate.

[0012] According to some embodiments of the present invention, the first carbonate solution and / or the second carbonate solution comprises a surfactant.

[0013] According to some embodiments of the present invention, the surfactant includes at least one of ethylenediaminetetraacetic acid and sodium dodecylbenzenesulfonate.

[0014] According to some embodiments of the present invention, the proportion of the surfactant in the first carbonate solution is 0.4% to 2% by mass; and / or, the proportion of the surfactant in the second carbonate solution is 0.4% to 2%; and / or, the proportion of the surfactant in the third carbonate solution is 0.4% to 2%.

[0015] According to some embodiments of the present invention, the temperature of the first carbonate solution is 90°C to 100°C; and / or the temperature of the second mixed slurry is 90°C to 100°C.

[0016] According to some embodiments of the present invention, the temperature of the washing liquid during the washing process is 40° C. to 90° C.

[0017] The lithium carbonate according to the embodiment of the second aspect of the present invention is prepared by the preparation method according to the embodiment of the first aspect of the present invention.

[0018] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which: Figure 1 is a schematic diagram of a method for preparing lithium carbonate according to an embodiment of the present invention; Figure 2 This is a scanning electron microscope (SEM) image of lithium carbonate according to Example 1 of the present invention. DETAILED DESCRIPTION

[0020] Reference below Figure 1 The following describes a method for preparing lithium carbonate according to an embodiment of the first aspect of the present invention.

[0021] like Figure 1 As shown, the method for preparing lithium carbonate according to the first embodiment of the present invention comprises the following steps: First lithium precipitation treatment: adding the first lithium sulfate solution dropwise into the first carbonate solution to form a first mixed slurry; Second lithium precipitation treatment: taking at least a portion of the first mixed slurry as a back slurry, mixing the back slurry with the second carbonate solution to form a second mixed slurry, adding the second lithium sulfate solution dropwise to the second mixed slurry to form a third mixed slurry, and taking at least a portion of the third mixed slurry to separate crude lithium carbonate; Washing: Wash the crude lithium carbonate to obtain lithium carbonate.

[0022] Specifically, during the first lithium precipitation treatment, the first lithium sulfate solution is added dropwise to the first carbonate solution, and the lithium sulfate and carbonate react to generate lithium carbonate. Among them, due to the use of the dripping method, the reaction rate of lithium sulfate and carbonate is slowed down, so that the generation rate of lithium carbonate is easy to control, and the phenomenon of lithium carbonate polycrystal and / or peritectic caused by the rapid addition of a large amount of lithium sulfate is avoided, thereby improving the quality of the generated lithium carbonate to meet the use requirements of the battery.

[0023] At least part of the first mixed slurry is used as the back slurry to ensure the stability of the continuous lithium precipitation process system. The lithium carbonate in the back slurry can be used as a seed crystal to precipitate on the surface of the lithium carbonate seed crystal in the subsequent lithium precipitation process, reduce nucleation, further avoid the appearance of polycrystals and / or peritectics, reduce residual impurities, and facilitate the removal of impurities such as sulfate by washing, so that the purity of lithium carbonate is more consistent. At the same time, the excess carbonate in the back slurry can also be used to increase the excess coefficient of carbonate in the subsequent second lithium precipitation process, improve the purity and lithium precipitation rate, and save costs.

[0024] Reference Figure 2 The prepared lithium carbonate is battery-grade lithium carbonate, and its morphology is monodisperse rod-shaped crystals, that is, the prepared lithium carbonate has a rod-shaped crystal particle shape, and the lithium carbonate can be evenly distributed without agglomeration. The purity of the prepared lithium carbonate is ≥99.5%, and the main impurity content is: Ca 2+ ≤50ppm, Na + ≤250ppm and SO4 2- ≤800ppm.

[0025] According to the preparation method of lithium carbonate of the embodiment of the present invention, at least part of the first mixed slurry after the first lithium precipitation treatment is used as a back slurry, and the back slurry is mixed with the second carbonate solution and then the second lithium sulfate solution is added dropwise to prepare lithium carbonate. Thus, at least part of the first mixed slurry is used as a back slurry, which can ensure the stability of the continuous lithium precipitation process system, and the lithium carbonate in the back slurry can be used as a crystal seed, so that the subsequent lithium precipitation process is precipitated on the surface of the lithium carbonate seed, reducing nucleation, further avoiding the appearance of polycrystal and / or peritectic, reducing impurity residues, and facilitating the use of washing to remove impurities such as sulfate, so that the purity consistency of lithium carbonate is higher. At the same time, the excess carbonate in the back slurry can also be used to increase the excess coefficient of carbonate in the subsequent second lithium precipitation treatment, improve the purity and lithium precipitation rate, and save costs.

[0026] According to some embodiments of the present invention, referring to Figure 1 , at least one third lithium precipitation treatment: take at least part of the third mixed slurry as the back slurry, mix the back slurry with the third carbonate solution, add the third lithium sulfate solution to form a fourth mixed slurry, at least part of the fourth mixed slurry as the back slurry, take at least part of the fourth mixed slurry to separate the crude lithium carbonate. That is to say, at least part of the third mixed slurry after the second lithium precipitation treatment can continue to be used as the back slurry, participate in the back slurry process, and ensure the stability of the continuous lithium precipitation process system. At the same time, the lithium carbonate in the third mixed slurry can be used as a seed crystal, so that the subsequent lithium precipitation process (third lithium precipitation treatment) is precipitated on the surface of the lithium carbonate seed crystal. In addition, the excess carbonate in the third mixed slurry can be used. As a result, it is conducive to the full utilization of the back slurry in the third mixed slurry.

[0027] At least part of the fourth mixed slurry after the third lithium precipitation treatment can be used as a back slurry to participate in another third lithium precipitation treatment, thereby extending the length of the back slurry process. Among them, the third lithium precipitation treatment can be once, twice or three times. But not limited to this. At least part of the fourth mixed slurry after each third lithium precipitation treatment can be separated into crude lithium carbonate, thereby ensuring the output of lithium carbonate in each third lithium precipitation treatment, improving the stability and sustainability of the lithium precipitation process, that is, continuously preparing lithium carbonate.

[0028] Furthermore, the molar ratio of lithium sulfate in the first lithium sulfate solution to carbonate in the first carbonate solution is 1:(1-3). As a result, the molar ratio of the first lithium sulfate solution to the first carbonate solution is reasonable, and carbonate ions are present in excess compared to lithium ions, ensuring that lithium ions can participate in the reaction as completely as possible, thereby increasing the yield of lithium carbonate in the first mixed slurry. At the same time, excessive use of the first carbonate solution is avoided, the fluidity of the first carbonate solution is guaranteed, the reaction reliability of lithium ions and carbonate ions is increased, and it is also beneficial to control the preparation cost of lithium carbonate.

[0029] For example, the first lithium sulfate may also include lithium carbonate, etc., which is not specifically limited here.

[0030] The mass ratio of the second lithium sulfate solution or the third lithium sulfate solution to the back pulp solution is 1: (5-20). Therefore, the amount of lithium carbonate in the back pulp solution and the amount of lithium sulfate in the second lithium sulfate solution or the third lithium sulfate solution are reasonably matched, thereby ensuring that the lithium carbonate can be fully grown with the lithium carbonate in the back pulp solution as a crystal seed, which is beneficial to improving the efficiency and quality of the prepared lithium carbonate.

[0031] According to some embodiments of the present invention, the lithium ion concentration in the first lithium sulfate solution, the second lithium sulfate solution and the third lithium sulfate solution is 20g / L to 50g / L. The lithium ion content in the first lithium sulfate solution, the second lithium sulfate solution and the third lithium sulfate solution is relatively reasonable, which is conducive to ensuring the lithium ion content in each dropwise addition process of the first lithium sulfate solution, the second lithium sulfate solution and the third lithium sulfate solution. Thus, it can be ensured that lithium carbonate is produced in each dropwise addition, and the content of the produced lithium carbonate is relatively reasonable, which can avoid the occurrence of polycrystal and / or peritectic phenomenon due to a high lithium ion content, thereby reducing impurities in the produced lithium carbonate and improving the quality of lithium carbonate.

[0032] The concentrations of the first carbonate solution, the second carbonate solution and the third carbonate solution are 200g / L to 300g / L. The concentrations of the first carbonate solution, the second carbonate solution and the third carbonate solution are relatively reasonable, so that it is easy to ensure that the concentration of the first carbonate solution is relatively reasonable, the concentration of the second mixed slurry formed by the second carbonate solution and the back slurry is relatively reasonable, and the concentration of the mixed solution of the third carbonate solution and the back slurry is relatively reasonable. Thus, it is beneficial to ensure the quality of the lithium carbonate generated in the first carbonate solution and the first lithium sulfate, the quality of the lithium carbonate generated by the second mixed slurry and the second lithium sulfate solution, the quality of the lithium carbonate generated by the mixed solution of the third carbonate solution and the back slurry and the third lithium sulfate solution, avoid the phenomenon of polycrystal and / or peritectic in the generated lithium carbonate, that is, avoid the problem of more impurities in the lithium carbonate caused by the high carbonate ion concentration, make it easy to remove impurities in the prepared crude carbonate, so as to improve the purity of the lithium carbonate and improve the consistency of the prepared lithium carbonate.

[0033] According to other embodiments of the present invention, the first carbonate solution, the second carbonate solution and the third carbonate solution are independently selected from at least one of sodium carbonate, ammonium carbonate and potassium carbonate. Among them, sodium carbonate is relatively mild in the reaction and can avoid the occurrence of side reactions caused by excessive alkalinity. Ammonium carbonate has a high reactivity at room temperature, and carbonate ions can react rapidly with lithium ions. Potassium carbonate has a high solubility in water and can quickly dissolve to form a uniform solution. Sodium carbonate, ammonium carbonate and potassium carbonate react with lithium ions as carbonates to generate lithium carbonate, all of which have the advantages of wide sources and low cost, which is conducive to reducing the preparation cost of lithium carbonate. At the same time, sodium carbonate, ammonium carbonate and potassium carbonate all have high reactivity, high solubility, strong alkalinity and good thermal stability, which is conducive to improving the preparation efficiency of lithium carbonate.

[0034] According to some embodiments of the present invention, the second lithium precipitation treatment further comprises: taking at least part of the first mixed slurry to separate crude lithium carbonate. At least part of the crude lithium carbonate in the first mixed slurry is separated, which is conducive to the gradual extraction of lithium carbonate, thereby ensuring the continuity of lithium carbonate production and the preparation efficiency of lithium carbonate.

[0035] It should be noted that the crude lithium carbonate can be washed separately in each step or washed together after accumulating a certain amount.

[0036] According to some more embodiments of the present invention, the first carbonate solution and / or the second carbonate solution include a surfactant. The presence of a surfactant can affect the reaction rate by changing the dispersion state, wettability and interfacial properties of carbonate in the first carbonate solution and / or the second carbonate solution. For example, the surfactant plays a dispersing effect on carbonate particles, and can make carbonate particles evenly dispersed in the liquid, avoid the reunion between particles, further increase the effective contact area between carbonate ions and lithium ions, promote the reaction, and improve the reaction rate. At the same time, the adsorption of the surfactant can make the surface of the lithium carbonate particles generated with the same charge, thereby generating an electrostatic repulsion force, preventing the reunion between the lithium carbonate particles, so that the lithium carbonate particles can be evenly dispersed in the liquid medium, that is, the polycrystal and / or peritectic phenomenon of lithium carbonate and the situation of lithium carbonate crystal surface adsorption can be reduced, and the monodisperse rod-shaped crystal state of the prepared lithium carbonate is guaranteed.

[0037] Furthermore, the surfactant includes at least one of ethylenediaminetetraacetic acid (EDTA) and sodium dodecylbenzene sulfonate (SDBS). There are four carboxyl groups and two amino groups in the EDTA molecule, which enables EDTA to form multiple coordination bonds with metal ions and has strong complexing ability. For example, EDTA can react with metal ions (Ca 2+ and / or Na + ) complexation, which makes it easy to remove impurities on the surface of lithium carbonate, which is beneficial to improve the purity of the prepared lithium carbonate.

[0038] The molecular structure of SDBS is mainly composed of the lipophilic dodecylbenzene part and the hydrophilic sulfonic acid part. The sulfonic acid group will be ionized in the aqueous solution, making the molecule negatively charged. An appropriate amount of SDBS can form a micellar structure in the aqueous solution, reduce the surface tension of the aqueous solution, and make the impurities on the surface of lithium carbonate easy to be washed away.

[0039] Therefore, using at least one of ethylenediaminetetraacetic acid and sodium dodecylbenzenesulfonate as a surfactant is beneficial to the dispersion of lithium carbonate crystals, avoiding the occurrence of polycrystal formation, and at the same time helps to reduce the difficulty of removing impurities on the surface of lithium carbonate, thereby helping to improve the preparation efficiency and purity of lithium carbonate.

[0040] According to some specific embodiments of the present invention, the proportion of surfactant in the first carbonate solution is 0.4% to 2% by mass. The content of surfactant in the first carbonate solution is relatively reasonable, which is conducive to giving full play to the role of surfactant, can significantly improve the dispersion stability of carbonate particles, and help to improve the quality of prepared lithium carbonate. At the same time, the fluidity of the first carbonate solution is guaranteed, and the carbonate particles in the first carbonate solution are prevented from agglomerating, thereby improving the dispersion stability of the first carbonate solution.

[0041] The proportion of surfactant in the second carbonate solution is 0.4% to 2%. The content of surfactant in the second carbonate solution is relatively reasonable, which can give full play to the role of the surfactant, improve the quality of the prepared lithium carbonate, avoid the agglomeration of carbonate particles in the second carbonate solution, ensure the fluidity of the second carbonate solution, and thus improve the dispersion stability of the second carbonate solution.

[0042] The proportion of surfactant in the third carbonate solution is 0.4% to 2%. The content of surfactant in the third carbonate solution is relatively reasonable, which can significantly improve the dispersion stability of carbonate particles and help improve the quality of prepared lithium carbonate. At the same time, avoiding excessive surfactants can prevent carbonate particles in the third carbonate solution from agglomerating, ensure the fluidity of the third carbonate solution, and thus improve the dispersion stability of the third carbonate solution.

[0043] According to some embodiments of the present invention, the temperature of the first carbonate solution is 90° C. to 100° C. The temperature of the first carbonate solution is relatively reasonable, meeting the dissolution temperature requirements of carbonates and the like in the first carbonate solution, thereby facilitating the uniformity of the first carbonate solution, facilitating the consistency of lithium carbonate crystals formed by the reaction of carbonate ions and lithium ions, and avoiding the occurrence of polycrystal and / or peritectic phenomena in lithium carbonate crystals.

[0044] The temperature of the second mixed slurry is 90° C. to 100° C. The temperature of the second mixed slurry is relatively reasonable, which fully ensures that the carbonate in the second mixed slurry is dissolved, so as to improve the stability of the reaction between the lithium ions in the second lithium sulfate and the carbonate ions in the second mixed slurry, so as to improve the quality of the prepared lithium carbonate crystals.

[0045] In addition, the temperature of the washing liquid during the washing process is 40°C to 90°C. The temperature of the washing liquid is relatively reasonable, ensuring that Na + and SO4 2- The dissolution of ions in the washing liquid is beneficial to remove impurities on the surface of the crude lithium carbonate, improve the purity of the lithium carbonate, and make the prepared lithium carbonate meet the use requirements of the battery. The washing liquid can be deionized water.

[0046] Preferably, the temperature of the washing liquid is 40° C. to 50° C. Thus, the washing temperature requirement of impurities on the surface of the crude lithium carbonate can be met while reducing the use of energy such as combustion gas, which is beneficial to controlling the preparation cost of lithium carbonate.

[0047] For example, the preparation process of lithium carbonate may specifically be: 1. Heat the first sodium carbonate solution to 90°C to 100°C; 2. Slowly drip the first lithium sulfate solution, and the dripping time is controlled within 1 hour to 3 hours, so that the molar ratio of the first lithium sulfate solution to the first sodium carbonate is 1 to 3 times.

[0048] 3. After the dropwise addition is completed, a portion of the first mixed slurry is taken as a back slurry and added to the second sodium carbonate solution, and the temperature is maintained at 90°C to 100°C; 4. Slowly add the second lithium sulfate solution dropwise, the amount of the second lithium sulfate added is 1 / 5 to 1 / 20 of the mass of the slurry; 5. After the addition is completed, a portion of the third mixed slurry is taken as a back slurry and added to the third sodium carbonate solution, and the temperature is maintained at 90°C to 100°C; 6. Slowly add the third lithium sulfate solution dropwise, the amount of the third lithium sulfate added is 1 / 5 to 1 / 20 of the mass of the slurry; 7. After the dropwise addition of the fourth mixed slurry is completed, a portion of the fourth mixed slurry is taken as a re-slurry to repeat the re-slurry treatment; 8. The remaining lithium carbonate mixture after lithium precipitation is pumped into a centrifuge for separation. The separated crude lithium carbonate enters the washing process for stirring and washing. The Na + and SO4 2- The ions are washed away with hot deionized water to obtain battery-grade lithium carbonate.

[0049] The lithium carbonate according to the embodiment of the second aspect of the present invention is prepared by the preparation method according to the embodiment of the first aspect of the present invention.

[0050] According to the lithium carbonate of the embodiment of the present invention, the lithium carbonate prepared by the above-mentioned preparation method has a high purity and can reach the battery grade, which is conducive to meeting the use requirements of the battery.

[0051] The embodiments of the present invention are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention. In addition, if not explicitly stated, all reagents used in the following embodiments are commercially available, or can be synthesized according to this article or known methods, and the reaction conditions not listed are also easily available to those skilled in the art.

[0052] It should be noted that the lithium carbonate prepared below can be divided into the first lithium carbonate, the second lithium carbonate, the third lithium carbonate and the fourth lithium carbonate according to the order of the preparation steps.

[0053] Example 1 The Li of the lithium sulfate solution used in Example 1 + The concentration is 35 g / L, and the concentration of the sodium carbonate solution used is 250 g / L.

[0054] 1. Heat 464 g of the first sodium carbonate solution to 90° C.; 2. Slowly drip the first lithium sulfate solution, the dripping time is controlled within 2 hours, the addition amount of the first lithium sulfate is 628.2 g, wherein the molar ratio of lithium sulfate in the first lithium sulfate solution to sodium carbonate in the first sodium carbonate solution is 1:1.2; 3. After the dropwise addition is completed, 1000 g of the first mixed slurry is taken as the back slurry 1 and added into 58 g of the second sodium carbonate solution as the second mixed slurry, and the temperature of the second mixed slurry is maintained at 90° C.; 4. Slowly add the second lithium sulfate solution dropwise, the amount of the second lithium sulfate solution added is 1 / 10 of the mass of the slurry; 5. After the addition is completed, a portion of the third mixed slurry is taken as the back slurry 2 for the third lithium precipitation treatment to obtain a fourth mixed slurry, wherein 1000 g of the back slurry, 58 g of the third sodium carbonate solution, and the amount of the third lithium sulfate solution added is 1 / 10 of the mass of the back slurry; 6. Take at least part of the fourth mixed slurry as the back slurry 3, react to form a fifth mixed slurry, wherein 1000g of the back slurry, 58g of the sodium carbonate solution, and the amount of the third lithium sulfate solution added is 1 / 10 of the mass of the back slurry; 7. Take at least part of the fifth mixed slurry as the back slurry 4, react to form a sixth mixed slurry, wherein the mass of the back slurry and the third carbonate solution are 1000g of the back slurry and 58g of the sodium carbonate solution, respectively, and the amount of the third lithium sulfate solution added is 1 / 10 of the mass of the back slurry; 8. The remaining parts of the first mixed slurry, the third mixed slurry, the fourth mixed slurry, the fifth mixed slurry and the sixth mixed slurry are separated by centrifuges, and the separated crude lithium carbonate enters the washing process. sequence Stir and wash, dissolve Na in water + and SO4 2- The ions are washed away by hot deionized water to obtain the first lithium carbonate, the second lithium carbonate, the third lithium carbonate and the fourth lithium carbonate.

[0055] Example 2 Example 2 is substantially the same as Example 1, except that in step 2, the molar ratio of lithium sulfate in the first lithium sulfate solution to sodium carbonate in the first sodium carbonate solution is 1:2.2.

[0056] Example 3 Example 3 is substantially the same as Example 1, except that in step 2, the molar ratio of lithium sulfate in the first lithium sulfate solution to sodium carbonate in the first sodium carbonate solution is 1:3.

[0057] Example 4 Example 4 is substantially the same as Example 1, except that the amount of lithium sulfate solution added in steps 4-7 is 1 / 20 of the mass of the back slurry.

[0058] Example 5 Example 5 is substantially the same as Example 1, except that the amount of lithium sulfate solution added in steps 4-7 is 1 / 5 of the mass of the slurry.

[0059] Example 6 Example 6 is basically the same as Example 1, except that the lithium sulfate solution used is Li + The concentration is 20 g / L, and the concentration of the sodium carbonate solution used is 200 g / L.

[0060] Example 7 Example 7 is basically the same as Example 1, except that the lithium sulfate solution used is Li + The concentration is 50 g / L, and the concentration of the sodium carbonate solution used is 300 g / L.

[0061] Example 8 Example 8 is substantially the same as Example 1, except that 0.4 wt % EDTA is added to the sodium carbonate solution added in each step.

[0062] Comparative Example The Li of the lithium sulfate solution used in the comparative example + The concentration is 35 g / L, and the concentration of the sodium carbonate solution used is 250 g / L.

[0063] 1. Heat 464 g of the first sodium carbonate solution to 95° C. 2. Slowly drip the first lithium sulfate solution, and the dripping time is controlled within 2 hours, wherein the addition amount of the first lithium sulfate is 628.2 g, and the molar ratio of lithium sulfate in the first lithium sulfate solution to sodium carbonate in the first sodium carbonate solution is 1:1.2.

[0064] 3. After the addition is completed, all the slurry is separated by a centrifuge. The separated crude lithium carbonate enters the washing process for stirring and washing. The Na + and SO4 2- The ions are washed away with hot deionized water to obtain lithium carbonate.

[0065] 4. The batch method was repeated four times.

[0066] Performance Testing (1) Purity test With reference to GB / T 11064.1-2013, the purity was tested by acid-base titration using a potentiometric titrator. The test results are shown in Table 1.

[0067] Table 1: Purity comparison of lithium carbonate prepared in Example and Comparative Example

[0068] (2) SO4 2- Content test Refer to GB / T 31197-2014 and use ion chromatography to test SO4 2- The test results are shown in Table 2.

[0069] Table 2: SO4 in lithium carbonate prepared in Examples and Comparative Examples 2- Content comparison

[0070] (3) Scanning electron microscope test The morphology test was carried out using a scanning electron microscope. The test results are as follows: Figure 2 shown.

[0071] Test results analysis Reference Figure 2 Compared with the comparative example, the lithium carbonate prepared in Examples 1-4 has a rod-shaped crystal particle shape, a more uniform distribution, and no agglomeration. Referring to the data in Tables 1 and 2, at the same time, for Ca 2+ and Na + The content of SO4 was detected and found that the impurity content (SO4 2- , Ca 2+ and Na + ) is less and has higher purity, and the above lithium carbonates are suitable for use in batteries.

[0072] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example.

[0073] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for preparing lithium carbonate, characterized in that: The steps include: First lithium precipitation treatment: adding the first lithium sulfate solution dropwise into the first carbonate solution to form a first mixed slurry; Second lithium precipitation treatment: taking at least a portion of the first mixed slurry as a back slurry, mixing the back slurry with a second carbonate solution to form a second mixed slurry, adding a second lithium sulfate solution dropwise to the second mixed slurry to form a third mixed slurry, and taking at least a portion of the third mixed slurry to separate crude lithium carbonate; Washing: washing the crude lithium carbonate to obtain lithium carbonate.

2. The method for preparing lithium carbonate according to claim 1, characterized in that: At least one third lithium precipitation treatment: taking at least a portion of the third mixed slurry as a back slurry, mixing the back slurry with a third carbonate solution, adding a third lithium sulfate solution to form a fourth mixed slurry, taking at least a portion of the fourth mixed slurry as a back slurry, and taking at least a portion of the fourth mixed slurry to separate crude lithium carbonate.

3. The method for preparing lithium carbonate according to claim 2, characterized in that: The molar ratio of lithium sulfate in the first lithium sulfate solution to carbonate in the first carbonate solution is 1:(1-3); and / or, The mass ratio of the second lithium sulfate solution or the third lithium sulfate solution to the slurry is 1:(5-20).

4. The method for preparing lithium carbonate according to claim 2, characterized in that: The lithium ion concentration in the first lithium sulfate solution, the second lithium sulfate solution and the third lithium sulfate solution is 20 g / L to 50 g / L; and / or, The concentrations of the first carbonate solution, the second carbonate solution and the third carbonate solution are 200 g / L to 300 g / L.

5. The method for preparing lithium carbonate according to claim 2, characterized in that: The first carbonate solution, the second carbonate solution and the third carbonate solution are independently selected from at least one of sodium carbonate, ammonium carbonate and potassium carbonate.

6. The method for preparing lithium carbonate according to claim 1, characterized in that: The second lithium precipitation treatment further includes: taking at least a portion of the first mixed slurry to separate crude lithium carbonate.

7. The method for preparing lithium carbonate according to any one of claims 1 to 6, characterized in that: The first carbonate solution and / or the second carbonate solution comprises a surfactant.

8. The method for preparing lithium carbonate according to claim 7, characterized in that: The surfactant includes at least one of ethylenediaminetetraacetic acid and sodium dodecylbenzene sulfonate.

9. The method for preparing lithium carbonate according to claim 7, characterized in that: In terms of mass percentage, the surfactant accounts for 0.4% to 2% in the first carbonate solution; and / or, The proportion of the surfactant in the second carbonate solution is 0.4% to 2%; and / or, The surfactant accounts for 0.4% to 2% in the third carbonate solution.

10. The method for preparing lithium carbonate according to claim 1, characterized in that: The temperature of the first carbonate solution is 90°C to 100°C; and / or the temperature of the second mixed slurry is 90°C to 100°C.

11. The method for preparing lithium carbonate according to claim 1, characterized in that: The temperature of the washing liquid during the washing process is 40°C to 90°C.

12. A lithium carbonate, characterized in that: The lithium carbonate is prepared by the preparation method according to any one of claims 1-11.

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