Method and device for preparing lithium carbonate

Abstract

The present application provides a method and apparatus for preparing lithium carbonate, comprising the steps of: obtaining a lithium bicarbonate solution having a total concentration of calcium and magnesium ions of 0.0005% to 0.007%; mixing the lithium bicarbonate solution with sodium carbonate for a precipitation reaction to obtain refined lithium carbonate. The method provided by the present application achieves the purpose of preparing higher-purity lithium carbonate, and has a short process flow, reduces wastewater generation, improves lithium recovery, and is conducive to industrial production.

Description

Technical Field

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

[0002] As a raw material for the cathode of lithium-ion batteries, lithium carbonate has been gaining increasing attention in recent years, with demand for higher-purity refined lithium carbonate, in particular, increasing. Refined lithium carbonate is typically prepared from lithium bicarbonate. However, current processes for preparing refined lithium carbonate often contain impurities such as calcium and magnesium, which are difficult to effectively remove. This makes it difficult to guarantee the quality of the resulting refined lithium carbonate, making it unsuitable for direct use as a raw material for synthesizing cathode materials for lithium-ion batteries.

[0003] At present, ion exchange resin is generally used to remove impurities such as calcium and magnesium in the preparation process of refined lithium carbonate. However, lithium loss will occur during the resin decomposition process, and the resin needs to be regenerated after use. During the regeneration, a large amount of wastewater will be generated. Lithium will be entrained in this wastewater, further causing lithium loss and reducing the lithium recovery rate. Summary of the Invention

[0004] The present application aims to improve at least one of the technical problems existing in the prior art. To this end, the present application provides a method and apparatus for preparing lithium carbonate.

[0005] According to a technical solution of the present application, a method for preparing lithium carbonate is provided, comprising the following steps:

[0006] Obtaining a lithium bicarbonate solution, wherein the total concentration of calcium and magnesium ions in the lithium bicarbonate solution is 0.0005%-0.007%;

[0007] The lithium bicarbonate solution is mixed with sodium carbonate to carry out precipitation reaction to obtain refined lithium carbonate.

[0008] In the above technical solution of the present application, in the process of mixing lithium bicarbonate and sodium carbonate for precipitation reaction, the role of sodium carbonate is to react chemically with lithium bicarbonate to generate lithium carbonate, and the generated lithium carbonate will precipitate in solid form, while impurities such as calcium and magnesium ions in the lithium bicarbonate solution are mainly present in the solution after the precipitation reaction. The lithium carbonate and impurities such as calcium and magnesium ions can be separated from each other by solid-liquid separation, thereby obtaining refined lithium carbonate with higher purity.

[0009] Compared to existing ion exchange resin impurity removal methods, this solution does not require resin regeneration during the precipitation reaction, thereby minimizing the problem of significant lithium loss during resin desorption and regeneration. This achieves the goal of producing high-purity lithium carbonate, while also simplifying the process, reducing wastewater generation, and improving lithium recovery, making it more suitable for industrial production.

[0010] Optionally, the preparation method specifically comprises: adding a mixed solution of sodium carbonate and lithium carbonate to the lithium bicarbonate solution to obtain a precipitation solution, subjecting the precipitation solution to a precipitation reaction to obtain a lithium carbonate precipitate and a post-precipitation liquid, wherein the post-precipitation liquid comprises sodium bicarbonate and lithium bicarbonate, and post-treating the lithium carbonate precipitate to obtain refined lithium carbonate;

[0011] Preferably, in the mixed solution of sodium carbonate and lithium carbonate, the mass fraction of sodium carbonate is 21-25%, the mass fraction of lithium carbonate is 1.5-2%, and the mass fraction of lithium carbonate crystals is 0.2-0.6%;

[0012] Preferably, the addition rate of the mixed solution of sodium carbonate and lithium carbonate is 0.15-0.4m 3 / min;

[0013] Preferably, the molar ratio of sodium carbonate to lithium bicarbonate in the precipitation solution is 2.05-2.15:1;

[0014] Preferably, the precipitation reaction temperature is 46-87°C;

[0015] Preferably, the precipitation reaction is carried out under stirring at a speed of 5-18 rpm;

[0016] Preferably, the average particle size of the lithium carbonate precipitate is 100-300 μm;

[0017] Preferably, the total concentration of calcium and magnesium ions in the lithium bicarbonate solution is 0.001%-0.007%;

[0018] Preferably, the total concentration of calcium and magnesium ions in the refined lithium carbonate is ≤0.0001%.

[0019] Optionally, the preparation method further comprises:

[0020] Carrying out carbonization reaction between crude lithium carbonate and carbon dioxide raw material to obtain the lithium bicarbonate solution;

[0021] Preferably, the pressure of the carbonization reaction is 0.02-0.2 MPa;

[0022] Preferably, the temperature of the carbonization reaction is 30-55°C;

[0023] Preferably, the volume fraction of carbon dioxide in the carbon dioxide raw material is 80-99%.

[0024] Optionally, before the carbonization reaction of the crude lithium carbonate and the carbon dioxide raw material, the preparation method further comprises:

[0025] The crude lithium carbonate is stirred and washed to obtain a stirring liquid and a stirring residue, the stirring residue is pulped to obtain a slurry, and the slurry is subjected to the carbonization reaction with a carbon dioxide raw material to obtain the lithium bicarbonate solution;

[0026] Preferably, the stirring and washing time is 0.5-1.5h;

[0027] Preferably, the solid content of the agitation and washing liquid is 30-40%;

[0028] Preferably, the mass fraction of sulfate in the stirred and washed residue is ≤0.45%, and the mass fraction of sodium ions is ≤0.3%;

[0029] Preferably, the solid content of the slurry is 4.5-6%.

[0030] Optionally, before subjecting the lithium bicarbonate solution to a precipitation reaction, the preparation method further comprises:

[0031] The lithium bicarbonate solution is filtered to obtain a filter residue and a filtered lithium bicarbonate solution, and the filtered lithium bicarbonate solution is subjected to a precipitation reaction.

[0032] Optionally, before subjecting the lithium bicarbonate solution to a precipitation reaction, the preparation method further comprises:

[0033] adding a neutralizing agent to the lithium bicarbonate solution to carry out a neutralization reaction, and then carrying out a precipitation reaction;

[0034] Preferably, the neutralizing agent comprises lithium hydroxide and / or sodium hydroxide solution;

[0035] Preferably, the mass fraction of the lithium hydroxide and / or sodium hydroxide solution is 12-25%;

[0036] Preferably, the mass ratio of the lithium hydroxide and / or sodium hydroxide solution to the lithium bicarbonate solution is 0.02-0.09:1;

[0037] Preferably, the pH value of the neutralization reaction is 11.5-12.5.

[0038] Optionally, the preparation method further comprises:

[0039] Purifying the washing liquid to obtain a mixed solution of sodium sulfate and lithium sulfate;

[0040] electrolyzing the mixed solution of sodium sulfate and lithium sulfate to obtain an alkaline solution and a sulfuric acid solution;

[0041] Leaching the sulfuric acid solution and the filter residue to obtain a lithium-containing leachate;

[0042] mixing the lithium-containing leachate with the precipitation solution to perform a precipitation reaction;

[0043] Preferably, the mass fraction of the sulfuric acid solution is 25-45%;

[0044] Preferably, the mass ratio of the lithium-containing leachate to the precipitation solution is 0.005-0.03:1;

[0045] Preferably, the mass of the agitation and washing liquid participating in the electrolysis reaction accounts for 28-67% of the total mass of the agitation and washing liquid.

[0046] Optionally, the preparation method further comprises:

[0047] Purifying the washing liquid to obtain a mixed solution of sodium sulfate and lithium sulfate;

[0048] electrolyzing the mixed solution of sodium sulfate and lithium sulfate to obtain an alkaline solution and a sulfuric acid solution;

[0049] Using the alkali solution as the neutralizing agent for the neutralization reaction;

[0050] Preferably, the alkali solution comprises sodium hydroxide and / or lithium hydroxide solution;

[0051] Preferably, the mass of the agitation and washing liquid participating in the electrolysis reaction accounts for 28-67% of the total mass of the agitation and washing liquid.

[0052] Optionally, the preparation method further comprises: performing a decomposition reaction on the precipitated liquid to obtain a gas product and a mixed solution of sodium carbonate and lithium carbonate, and using the mixed solution of sodium carbonate and lithium carbonate for the precipitation reaction;

[0053] Preferably, the temperature of the decomposition reaction is 165-248°C;

[0054] Preferably, the decomposition reaction time is 0.6-3h;

[0055] Preferably, the volume fraction of carbon dioxide in the gas product is 45-85%;

[0056] Preferably, the gas product is purified to obtain a lithium-containing solution and high-purity carbon dioxide, and the high-purity carbon dioxide is used as a carbon dioxide raw material for the carbonization reaction;

[0057] Preferably, the volume fraction of carbon dioxide in the high-purity carbon dioxide is 80-99%.

[0058] Optionally, before subjecting the lithium bicarbonate solution to a precipitation reaction, the preparation method further comprises:

[0059] adding a neutralizing agent to the lithium bicarbonate solution to carry out a neutralization reaction, and then carrying out a precipitation reaction;

[0060] The lithium-containing solution is used as a reaction raw material for the neutralization reaction.

[0061] According to another technical solution of the present application, a lithium carbonate preparation device is provided, comprising a carbonization system and a precipitation system connected in sequence, wherein the carbonization system is used to subject crude lithium carbonate to a carbonization reaction to obtain a lithium bicarbonate solution; and the precipitation system is used to subject the lithium bicarbonate solution to a precipitation reaction to obtain refined lithium carbonate.

[0062] Optionally, a filtration system is further included, and the carbonization system, the filtration system and the precipitation system are connected in sequence.

[0063] Optionally, a neutralization system is further included, and the carbonization system, the neutralization system and the precipitation system are connected in sequence.

[0064] Optionally, it also includes a stirring and washing system, a purification system, an electrolysis system and a leaching system, and the stirring and washing system, the carbonization system, the filtration system and the precipitation system are connected in sequence, and the stirring and washing system, the purification system, the electrolysis system, the leaching system and the precipitation system are connected in sequence, and the filtration system is connected to the leaching system.

[0065] Optionally, it further includes a stirring and washing system, a purification system and an electrolysis system, wherein the stirring and washing system, the carbonization system, the neutralization system and the precipitation system are connected in sequence, and the stirring and washing system, the purification system, the electrolysis system and the neutralization system are connected in sequence.

[0066] Optionally, a decomposition system is further included, and the decomposition system is connected to the precipitation system and the carbonization system respectively.

[0067] Additional technical solutions and advantages of the present application will be partially given in the following description, and partially become apparent from the following description, or be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0069] Figure 1 Schematic diagram of a process for preparing lithium carbonate according to an embodiment of the present invention;

[0070] Figure 2 It is a schematic diagram of an embodiment of the lithium carbonate preparation device of the present application. DETAILED DESCRIPTION

[0071] It should be understood that the specific embodiments given herein are for the purpose of explaining to those skilled in the art and are merely illustrative rather than restrictive.

[0072] In the following description, many specific details are set forth to provide a thorough understanding of the present application. However, it will be apparent to one of ordinary skill in the art that specific details are not required to practice the present application. In other cases, well-known steps or operations are not described in detail to avoid obscuring the present application.

[0073] In this application, unless otherwise specified, pressure refers to gauge pressure, also known as relative pressure.

[0074] Solid content refers to the content of solids in a solution or slurry, and in this application specifically refers to the content of lithium carbonate solids in a solution or slurry.

[0075] Dry basis refers to a way of expressing the content of a component in wet solid or wet gas based on a unit mass of anhydrous solid or dry gas.

[0076] Wet basis refers to a method of expressing the content of a component in wet solids or wet gases based on a unit mass of wet solids or wet gases.

[0077] " range " disclosed in the present application is limited in the form of lower limit and / or upper limit, and given range is limited by selecting a lower limit and / or an upper limit, and selected lower limit and / or upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0078] The traditional method for preparing crude lithium carbonate is to carbonize the crude lithium carbonate to obtain lithium bicarbonate, and then pyrolyze the lithium bicarbonate to obtain lithium carbonate. When pyrolyzing lithium bicarbonate, a large number of lithium carbonate nuclei are first obtained by decomposing lithium bicarbonate, and then the required large-particle lithium carbonate is grown on the basis of the lithium carbonate nuclei. Since the pyrolysis process is difficult to control and the temperature rises and evaporates quickly, a large number of lithium carbonate nuclei will be produced, resulting in calcium and magnesium ions combining with the lithium carbonate nuclei during the pyrolysis process and introducing impurities. Therefore, it is necessary to perform ion exchange resin impurity removal before pyrolysis to reduce the content of impurities such as calcium and magnesium ions. Since lithium loss will occur during resin decomposition and the resin has poor selectivity, the wastewater discharge from resin regeneration is large, resulting in large investment in impurity removal, and the wastewater will bring out more lithium, resulting in large lithium loss.

[0079] For the above defects, refer to Figure 1 The process flow shown in the figure shows that the method for preparing lithium carbonate provided in the embodiment of the present application comprises at least the following steps: obtaining a lithium bicarbonate solution, wherein the total concentration (mass percentage concentration) of calcium and magnesium ions in the lithium bicarbonate solution is 0.0005%-0.007%; mixing the lithium bicarbonate solution with sodium carbonate to carry out a precipitation reaction to obtain refined lithium carbonate. In this embodiment, refined lithium carbonate is obtained by precipitation reaction, which realizes the separation of lithium carbonate and impurities, eliminates the need for resin impurity removal, greatly reduces wastewater discharge, avoids lithium loss caused by resin impurity removal, and improves lithium recovery rate.

[0080] In some optional embodiments, the preparation method specifically includes: adding a mixed solution of sodium carbonate and lithium carbonate to a lithium bicarbonate solution to obtain a precipitation solution, the precipitation solution undergoes a precipitation reaction to obtain a lithium carbonate precipitate and a post-precipitation liquid, the post-precipitation liquid includes sodium bicarbonate and lithium bicarbonate, and the lithium carbonate precipitate is post-treated to obtain refined lithium carbonate.

[0081] In this embodiment, sodium carbonate and lithium bicarbonate are added to carry out precipitation reaction, and the reaction equation includes:

[0082] 2LiHCO3+Na2CO3→2NaHCO3+Li2CO3.

[0083] According to the above formula, lithium bicarbonate can be converted into lithium carbonate precipitate, which can then be post-processed to obtain refined lithium carbonate. For example, the lithium carbonate precipitate can be centrifuged, dried, and pulverized to obtain refined lithium carbonate. Furthermore, since lithium carbonate is added during the precipitation reaction, the small particles of lithium carbonate added can serve as crystal nuclei. The lithium carbonate converted from lithium bicarbonate can adhere to the surface of the crystal nuclei, thereby promoting the formation of the lithium carbonate precipitate and facilitating the precipitation reaction.

[0084] In some optional embodiments, in a mixed solution of sodium carbonate and lithium carbonate, the mass fraction of sodium carbonate is 21-25%, the mass fraction of lithium carbonate is 1.5-2%, and the mass fraction of lithium carbonate crystals is 0.2-0.6%. In the present embodiment, the lithium carbonate in the mixed solution of sodium carbonate and lithium carbonate has reached a supersaturated state, and accordingly, lithium carbonate crystals refer to solid lithium carbonate that has failed to dissolve in the mixed solution of sodium carbonate and lithium carbonate. That is, in the mixed solution of sodium carbonate and lithium carbonate, a portion of lithium carbonate is completely dissolved so that lithium carbonate reaches saturation, and the other portion of lithium carbonate fails to dissolve and exists as lithium carbonate crystals. The total mass fraction of the two portions of lithium carbonate is 1.5-2%, and the mass fraction of the lithium carbonate crystals that have failed to dissolve is 0.2-0.6%.

[0085] Within the sodium carbonate concentration range of this embodiment, the precipitation reaction effect can be improved, ensuring that lithium bicarbonate can be converted into lithium carbonate as much as possible. In addition, the lithium carbonate crystals in this embodiment can directly serve as crystal nuclei, thereby promoting the precipitation reaction and allowing lithium bicarbonate to be quickly converted into lithium carbonate precipitate.

[0086] In some optional embodiments, the addition rate of the mixed solution of sodium carbonate and lithium carbonate is 0.15-0.4m 3 By controlling the addition rate of the mixed solution of sodium carbonate and lithium carbonate, it is beneficial to maintain the concentration of sodium carbonate and the supersaturation of lithium carbonate in the precipitation solution, thereby facilitating the growth of lithium carbonate crystals to obtain lithium carbonate precipitate.

[0087] In some optional embodiments, the molar ratio of sodium carbonate to lithium bicarbonate in the precipitation solution is 2.05-2.15: 1. By controlling the molar ratio of sodium carbonate to lithium bicarbonate in the precipitation solution within the above range, it is possible to ensure that lithium bicarbonate can react smoothly with sodium carbonate, thereby continuously producing refined lithium carbonate.

[0088] In some optional embodiments, the temperature of the precipitation reaction is 46-87 DEG C. The temperature of the precipitation reaction should not be too high, otherwise it will lead to the formation of a large number of crystal nuclei, and the crystal particles are fine, making it difficult to effectively separate lithium carbonate from solid-liquid separation; The temperature of the precipitation reaction should not be too low, otherwise it will lead to the formation of fewer crystal nuclei, and the crystal particles are large. The calcium and magnesium impurities in the crystal particles are seriously wrapped, causing the particle size of the obtained refined lithium carbonate to be difficult to meet the requirements, and the calcium and magnesium content are high. In the present embodiment, under the temperature range, it is now possible to ensure that the precipitation reaction is carried out smoothly, so that the lithium carbonate crystal nuclei grow stably, which is conducive to precipitating the lithium carbonate precipitation that meets the particle size requirements, and the calcium and magnesium content are low. For example, the temperature of the precipitation solution can be 46 DEG C, 50 DEG C, 55 DEG C, 60 DEG C, 65 DEG C, 70 DEG C, 75 DEG C, 80 DEG C, 85 DEG C, 87 DEG C or any value between 46-87 DEG C.

[0089] In some optional embodiments, precipitation reaction is carried out under stirring, and stirring speed is 5-18rpm.Stirring speed can affect the crystallinity of nucleus, and if stirring speed is too large, solution flow rate is accelerated, and shear nucleation rate can rapidly increase and produce a large amount of nucleus, causing foreign ions to be easily combined with nucleus, and stirring speed is too large to cause the probability of crystal fragmentation to break up to increase simultaneously;If stirring speed is too slow, crystal sedimentation can be caused, which is unfavorable for precipitation crystallization.Under suitable stirring speed in the present embodiment, it is ensured that nucleus can suspend and collide, grow, and the probability of nucleus fragmentation, large-scale occurrence of nucleus is reduced as much as possible, which is conducive to the stable generation of lithium carbonate precipitation.For example, the stirring speed of precipitation solution can be any numerical value between 5rpm, 6rpm, 8rpm, 10rpm, 12rpm, 14rpm, 16rpm, 18rpm or 5-18rpm.

[0090] In some optional embodiments, the average particle size of the lithium carbonate precipitate is 100-300 μm. Under the average particle size range in the present embodiment, when the lithium carbonate precipitate is subjected to post-processing, it is not only conducive to centrifugation, but also conducive to the particle size requirement of the lithium carbonate obtained after the pulverization that can meet the lithium carbonate of higher purity. By controlling the average particle size of the lithium carbonate precipitate, it is also possible to make the trace calcium and magnesium ions in the precipitation solution difficult to enter the crystal nucleus crystallization, thereby reducing the calcium and magnesium ion impurity content of the lithium carbonate, improving the purity of the lithium carbonate, and realizing that lithium carbonate of higher purity can be obtained without using resin for impurity removal.

[0091] For example, the average particle size of the lithium carbonate precipitate can be 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, 220 μm, 240 μm, 260 μm, 280 μm, 300 μm or any value between 100-300 μm.

[0092] Furthermore, since the average particle size of the lithium carbonate precipitate depends on factors such as the number of crystal nuclei, stirring speed, and supersaturation, and the same reaction conditions may have different effects on the precipitation reaction in different environments, in this embodiment, by exploring the precipitation process, the optimal crystallization under such process material conditions is achieved, so that the average particle size of the lithium carbonate precipitate is between 100-300 μm, which can also create conditions for subsequent post-processing steps such as drying, air flow crushing, mixed batch iron removal, and packaging.

[0093] In some optional embodiments, the total concentration of calcium and magnesium ions in the refined lithium carbonate is ≤0.0001%.

[0094] In some optional embodiments, the total concentration of calcium and magnesium ions in the lithium bicarbonate solution is 0.001%-0.007%.

[0095] In some optional embodiments, the preparation method further comprises: carbonizing the crude lithium carbonate with the carbon dioxide raw material to obtain a lithium bicarbonate solution. The reaction equation of the carbonization reaction includes:

[0096] Li2CO3+CO2+H2O→2LiHCO3.

[0097] In some optional embodiments, the pressure of the carbonization reaction is 0.02-0.2 MPa, which is beneficial to increasing the rate of the carbonization reaction and converting as much lithium carbonate as possible into lithium bicarbonate to facilitate the subsequent precipitation reaction.

[0098] In some optional embodiments, the temperature of the carbonization reaction is 30-55° C., which is conducive to converting lithium carbonate into lithium bicarbonate.

[0099] In some optional embodiments, the volume fraction of carbon dioxide in the carbon dioxide raw material is 80-99%.By selecting an appropriate carbon dioxide concentration, the rate of the carbonization reaction can be increased, which is conducive to a rapid and sufficient carbonization reaction between carbon dioxide and lithium carbonate.

[0100] Before crude lithium carbonate and carbon dioxide raw material are carried out carbonization reaction, preparation method also comprises: crude lithium carbonate is stirred and washed to obtain stirring washing liquid and stirring washing slag, stirring and washing slag is pulped to obtain slurries, slurries and carbon dioxide raw material are carried out carbonization reaction to obtain lithium bicarbonate solution.In the present embodiment, first crude lithium carbonate is stirred and washed to remove soluble impurities such as sodium ion, sulfate ion, chloride ion etc. that crude lithium carbonate contains, then the crude lithium carbonate solid pulping after stirring and washing is obtained slurries, so that lithium carbonate participates in reaction, and then slurries are carried out carbonization reaction to obtain lithium bicarbonate solution.Thus, both the removal of soluble impurities in crude lithium carbonate is achieved, crude lithium carbonate carbonization is also achieved to obtain lithium bicarbonate solution, which is conducive to subsequent precipitation of refined lithium carbonate from lithium bicarbonate solution.

[0101] In some optional embodiments, the stirring and washing time is 0.5-1.5 hours, during which soluble impurities such as sodium sulfate contained in the crude lithium carbonate can be fully removed, which is beneficial to the preparation of crude lithium carbonate.

[0102] In some optional embodiments, the solid content of the washing liquid is 30-40%, at which time the soluble impurities in the crude lithium carbonate can be removed as much as possible, and in subsequent steps, the washing liquid can be further utilized to ensure that the small amount of lithium entrained in the washing liquid can be recovered, thereby improving the lithium recovery rate.

[0103] In some optional embodiments, the mass fraction of sulfate in the stirred and washed slag is ≤0.45%, and the mass fraction of sodium ions is ≤0.3%; within the mass fraction ranges of sulfate and sodium ions in this embodiment, it is possible to ensure that sulfate and sodium ion impurities in the crude lithium carbonate are fully removed, thereby avoiding excessive concentrations of sulfate and sodium ions that affect the purity of the refined lithium carbonate.

[0104] In some optional embodiments, the solid content of the slurry is 4.5-6%, which is conducive to the full carbonization reaction between the lithium carbonate and carbon dioxide in the slurry, thereby improving the conversion rate of lithium carbonate to lithium bicarbonate.

[0105] In some optional embodiments, before subjecting the lithium bicarbonate solution to a precipitation reaction, the preparation method further comprises filtering the lithium bicarbonate solution to obtain a filter residue and a filtered lithium bicarbonate solution, and subjecting the filtered lithium bicarbonate solution to a precipitation reaction. In this embodiment, filtering can remove most of the insoluble impurities, such as calcium and magnesium, contained in the crude lithium carbonate, thereby improving the purity of the refined lithium carbonate obtained by precipitation.

[0106] In some optional embodiments, the filtration method includes at least one of plate and frame filtration, multi-media filtration, and ultrafiltration, preferably a combination of two-stage plate and frame filtration and one-stage ultrafiltration. Thus, the filtration method of this embodiment can improve the filtration efficiency of insoluble impurities such as calcium and magnesium, thereby fully removing insoluble impurities in the lithium bicarbonate solution.

[0107] In some optional embodiments, after filtering the lithium bicarbonate solution, the preparation method further includes: adding a neutralizer to the filtered lithium bicarbonate solution for a neutralization reaction, and then performing a precipitation reaction. In this embodiment, the use of a neutralizer to adjust the pH value can cause impurities such as calcium and magnesium to precipitate, thereby further removing impurities such as calcium and magnesium in the lithium bicarbonate solution, which is beneficial to improving the purity of the finally prepared refined lithium carbonate.

[0108] In some optional embodiments, the neutralizing agent includes lithium hydroxide and / or sodium hydroxide solution. In this embodiment, lithium hydroxide and / or sodium hydroxide solution are used for the neutralization reaction to minimize the introduction of impurities. The reaction equation includes:

[0109] LiHCO3+LiOH→Li2CO3+H2O,

[0110] Li2CO3+Ca 2+ →2Li + +CaCO3,

[0111] Mg 2+ +2OH - →Mg(OH)2.

[0112] In some optional embodiments, the mass fraction of the lithium hydroxide and / or sodium hydroxide solution (aqueous solution) is 12-25%. By selecting the appropriate concentration of lithium hydroxide and / or sodium hydroxide solution, the hydroxide ion concentration during the neutralization reaction can be regulated, resulting in more complete precipitation of impurities such as calcium and magnesium, while also avoiding the introduction of excessive solvent water into the lithium bicarbonate solution.

[0113] In some optional embodiments, the mass ratio of lithium hydroxide and / or sodium hydroxide solution to lithium bicarbonate solution is 0.02-0.09:1; in this embodiment, by controlling the relative amounts of lithium hydroxide and / or sodium hydroxide solution and lithium bicarbonate solution, it is beneficial to precipitate calcium and magnesium ions in the lithium bicarbonate solution, so as to facilitate the subsequent acquisition of higher purity refined lithium carbonate.

[0114] In some optional embodiments, the pH value of the neutralization reaction is 11.5-12.5. In this pH range, impurities such as calcium and magnesium ions can be precipitated to the greatest extent, thereby reducing the impact of impurities such as calcium and magnesium ions on the purity of refined lithium carbonate.

[0115] In some optional embodiments, the preparation method further includes: purifying the washing liquid to obtain a mixed solution of sodium sulfate and lithium sulfate; subjecting the mixed solution of sodium sulfate and lithium sulfate to an electrolytic reaction to obtain an alkaline solution and a sulfuric acid solution; using the alkaline solution as a neutralizer for a neutralization reaction; leaching the sulfuric acid solution and the filter residue to obtain a lithium-containing leachate; and mixing the lithium-containing leachate with a precipitation solution to perform a precipitation reaction.

[0116] Since the washing liquid contains a small amount of lithium ions, the washing liquid is treated in this embodiment to recover the lithium ions in the washing liquid, thereby improving the lithium recovery rate. Specifically, the washing liquid is first subjected to multi-stage impurity removal and purification to obtain a mixed solution of sodium sulfate and lithium sulfate in which the sum of the calcium ion and magnesium ion concentrations is less than 0.0015%, which can remove calcium and magnesium ion impurities as much as possible. Then, the mixed solution of sodium sulfate and lithium sulfate is subjected to an electrolytic reaction to obtain an alkaline solution and a sulfuric acid solution, wherein the alkaline solution includes sodium hydroxide and / or lithium hydroxide solution. The reaction equation includes:

[0117] Na2SO4+2H2O→2NaOH+H2SO4,

[0118] Li2SO4+2H2O→2LiOH+H2SO4.

[0119] Then, the sodium hydroxide and / or lithium hydroxide solution obtained by electrolysis is used as a neutralizing agent for a neutralization reaction to adjust the pH of the lithium bicarbonate solution and to remove impurities by precipitation. Therefore, no additional sodium hydroxide and / or lithium hydroxide needs to be consumed during the preparation process, and lithium ions in the agitation and washing liquid are fully recovered, thereby improving the recovery rate of lithium, reducing the amount of circulating water, and lowering the operating cost.

[0120] The sulfuric acid solution obtained by electrolysis is then subjected to a leaching reaction with the filter residue obtained in the aforementioned filtration step to leach out the lithium entrained in the filter residue. Specifically, the lithium carbonate in the filter residue after filtration and impurity removal is converted into lithium sulfate. The reaction equation includes:

[0121] H2SO4+Li2CO3→Li2SO4+CO2+H2O.

[0122] In this way, the lithium in the filter residue can be recovered as much as possible, and the leached lithium is subjected to a precipitation reaction to obtain refined lithium carbonate, thereby improving the purity of the refined lithium carbonate and the lithium recovery rate.

[0123] In some optional embodiments, the purification method includes at least one of precipitation, filtration, evaporation concentration and chelating resin adsorption. Preferably, precipitation and chelating resin adsorption are combined for purification to obtain a mixed solution of sodium sulfate and lithium sulfate with higher purity.

[0124] In some optional embodiments, the electrolysis voltage of the electrolysis reaction is 3.2-6.5 V, which is conducive to obtaining alkaline solution and sulfuric acid solution by electrolysis.

[0125] In some optional embodiments, the electrolysis current of the electrolysis reaction is 0.2-0.8 A / cm 2 At this time, it is conducive to electrolysis to obtain alkali solution and sulfuric acid solution.

[0126] In some optional embodiments, the quality of the washing liquid that participates in electrolytic reaction accounts for the 28-67% of the washing liquid total mass.Owing to may contain impurity such as sulfate radical, chlorion in the crude lithium carbonate, correspondingly also may have impurity such as sulfate radical, chlorion in the washing liquid, if all washing liquids are all carried out electrolysis recycling, may cause the phenomenon of foreign ion enrichment such as sulfate radical, chlorion to occur in the precipitation solution, cause the normal carrying out of influencing precipitation reaction.Therefore, in the present embodiment, select that part washing liquid is carried out electrolysis recycling, can reclaim the lithium in the washing liquid as much as possible like this, simultaneously also the too much situation of foreign ion can not occur.

[0127] In some optional embodiments, the sulfuric acid solution is concentrated and then subjected to a leaching reaction with the filter residue. The mass fraction of the concentrated sulfuric acid solution is 25-45%, which is conducive to fully leaching the lithium in the filter residue, thereby improving the lithium recovery rate.

[0128] In some optional embodiments, the filter residue having a sum of the mass percentages of calcium and magnesium ions ≤ 10% is used for a leaching reaction with a sulfuric acid solution. This can avoid excessive calcium and magnesium ion content in the lithium-containing leachate obtained by the leaching reaction, which may affect the normal progress of the precipitation reaction.

[0129] In some optional embodiments, the mass ratio of the lithium-containing leachate to the precipitation solution is 0.005-0.03:1. By controlling the amount of the lithium-containing leachate to be much smaller than the amount of the precipitation solution, the lithium-containing leachate can be allowed to participate in the precipitation reaction to precipitate lithium, while also preventing the lithium-containing leachate from introducing a large amount of impurity ions such as sulfate into the precipitation solution, thereby facilitating the normal progress of the precipitation reaction.

[0130] In some optional embodiments, the preparation method further includes: decomposing the liquid after precipitation to obtain a gas product and a mixed solution of sodium carbonate and lithium carbonate, purifying the gas product to obtain a lithium-containing solution and high-purity carbon dioxide, using the high-purity carbon dioxide as a reaction raw material for a carbonization reaction, and using the mixed solution of sodium carbonate and lithium carbonate for a precipitation reaction.

[0131] In this embodiment, the precipitated solution containing sodium bicarbonate and lithium bicarbonate can be heated and evaporated to decompose to obtain a gas product containing carbon dioxide and a mixed solution of sodium carbonate and lithium carbonate. The reaction equation includes:

[0132] 2NaHCO3→Na2CO3+CO2+H2O,

[0133] 2LiHCO3→Li2CO3+CO2+H2O.

[0134] The carbon dioxide contained in the gaseous product can be used for carbonization, achieving carbon dioxide recycling. Therefore, throughout the entire crude lithium carbonate preparation process, only a small amount of CO2 needs to be regularly added to maintain the normal progress of the carbonization reaction. A mixed solution of sodium carbonate and lithium carbonate can be used for precipitation, achieving the recycling of sodium carbonate and lithium carbonate. This eliminates the need for additional sodium carbonate, reduces the operating costs of the preparation process, improves operational stability, and achieves a circular economy.

[0135] In some optional embodiments, the decomposition reaction temperature is 165-248° C., and the decomposition reaction time is 0.6-3 h, which is conducive to the complete decomposition of sodium bicarbonate and lithium bicarbonate to obtain sodium carbonate and lithium carbonate.

[0136] In some optional embodiments, the volume fraction of carbon dioxide in the gas product is 45-85%, and the obtained gas product can be recycled for carbonization reaction after purification.

[0137] In some optional embodiments, the purification process includes cooling the gas product to remove liquid to obtain a lithium-containing solution, and then adsorbing impurities such as H2S / HCl / HF to obtain high-purity carbon dioxide with a volume fraction of ≥80%. The high-purity carbon dioxide is directly recycled back to the carbonization reaction. Furthermore, since the gas product produced by the decomposition reaction may carry a small amount of lithium in the form of gas-liquid entrainment, the purification process can allow the lithium entrained in the gas product to enter the lithium-containing solution, which is then used as a reaction raw material for the neutralization reaction to produce refined lithium carbonate, thereby further improving the lithium recovery rate.

[0138] In some optional embodiments, the volume fraction of carbon dioxide in the high-purity carbon dioxide is 80-99%. In this case, the high-purity carbon dioxide can be directly introduced into the crude lithium carbonate slurry to perform the carbonization reaction.

[0139] In some optional embodiments, the crude lithium carbonate comprises industrial-grade lithium carbonate, and the refined lithium carbonate comprises battery-grade lithium carbonate, thereby providing a method for preparing battery-grade lithium carbonate from industrial-grade lithium carbonate. The resulting battery-grade lithium carbonate has a product qualification rate of no less than 99.6%, and its quality meets the requirements of "YS / T 582-2013 Battery-Grade Lithium Carbonate," and can be directly used, for example, in the preparation of positive electrode materials for lithium-ion batteries.

[0140] Specifically, industrial-grade lithium carbonate is obtained from sources such as salt lake extraction, pre- and post-extraction of battery recycling, ores, and industrial by-products. Battery recycling includes recycled ferrophosphorus batteries and ternary batteries. Industrial-grade lithium carbonate is obtained by subjecting the recycled battery to reduction, leaching, impurity removal, concentration, sodium sulfate recovery, lithium precipitation, pulverization, drying, and magnetic material removal. The mass percentage of lithium carbonate in industrial-grade lithium carbonate is generally 75-95%, and it also contains a significant amount of solid impurities, primarily sodium, sulfate, chloride, calcium, and magnesium ions.

[0141] In the preparation method provided in this embodiment, impurities such as sodium ions, sulfate ions, chloride ions, calcium ions, and magnesium ions in industrial-grade lithium carbonate can be removed as much as possible, and the lithium in the industrial-grade lithium carbonate can be fully recovered, thereby obtaining battery-grade lithium carbonate with higher purity.

[0142] Reference Figure 1 and Figure 2 Another embodiment of the present application provides a lithium carbonate production apparatus comprising a carbonization system and a precipitation system connected in sequence. The carbonization system may include a carbonization tower for carbonizing crude lithium carbonate to obtain a lithium bicarbonate solution; the precipitation system may include a precipitation crystallizer for precipitating the lithium bicarbonate solution to obtain refined lithium carbonate.

[0143] In some optional embodiments, the preparation device also includes a filtration system, and the carbonization system, the filtration system and the precipitation system are connected in sequence. The filtration system can include filtration equipment such as plate and frame filtration equipment, multi-media filtration equipment and ultrafiltration equipment, etc., for filtering the lithium bicarbonate solution after the carbonization reaction to obtain filter residue and the filtered lithium bicarbonate solution. The filtration system in the present embodiment is preferably any two of plate and frame filtration equipment, multi-media filtration equipment and ultrafiltration equipment, and is further preferably plate and frame filtration equipment combined with multi-media filtration equipment for filtration or plate and frame filtration equipment combined with ultrafiltration equipment for filtration.

[0144] In some optional embodiments, the preparation device further includes a neutralization system, wherein the carbonization system, the filtration system, the neutralization system, and the precipitation system are sequentially connected. The neutralization system may include a neutralization tank for performing a neutralization reaction on the filtered lithium bicarbonate solution.

[0145] In some optional embodiments, the preparation device also includes a stirring and washing system, a purification system, an electrolysis system and a leaching system, the stirring and washing system, the carbonization system, the filtration system, the neutralization system and the precipitation system are connected in sequence, and the stirring and washing system, the purification system, the electrolysis system, the leaching system and the precipitation system are connected in sequence, the filtration system is connected to the leaching system, and the electrolysis system is connected to the neutralization system.

[0146] The agitation and washing system may include an agitation and washing tank for agitating and washing crude lithium carbonate to obtain a crude lithium carbonate solid and a washing liquid. The purification system may include a purification device, and the purification device may provide the washing liquid for precipitation, filtration, evaporation concentration and / or chelate resin adsorption to purify the washing liquid to obtain a mixed solution of sodium sulfate and lithium sulfate. The electrolysis system may include an electrolytic cell for electrolyzing the mixed solution of sodium sulfate and lithium sulfate to obtain an alkali solution and a sulfuric acid solution, and the alkali solution may be fed into a neutralization system for a neutralization reaction. The leaching system may include a leaching tank for leaching the concentrated sulfuric acid solution with a filter residue to obtain a lithium-containing leachate, and the lithium-containing leachate may be fed into a precipitation system for a precipitation reaction.

[0147] In some optional embodiments, the electrolytic cell is selected from at least one of a bipolar membrane electrolytic cell, an ion membrane electrolytic cell, a diaphragm electrolytic cell, an alkaline electrolytic cell, a proton membrane electrolytic cell, an anion electrolytic cell, and a solid-state electrolytic cell.

[0148] In some optional embodiments, the preparation apparatus further includes a decomposition system, which is connected to the precipitation system and the carbonization system. The decomposition system may include a decomposition kettle for decomposing a mixed solution of sodium bicarbonate and lithium bicarbonate to produce a gas product and a mixed solution of sodium carbonate and lithium carbonate, and using the mixed solution of sodium carbonate and lithium carbonate for the precipitation reaction.

[0149] Following examples more specifically describe the content disclosed in the present application, and these embodiments are only for illustrative explanation, because carrying out various modifications and variation within the scope of the present application's disclosure is obvious to those skilled in the art. Unless otherwise stated, all parts, percentages and ratios reported in the following examples are all based on mass meters, and all reagents and raw materials used in the examples are all commercially available or synthesized according to a conventional method, and the instrument used in the examples is all commercially available. It should be understood that the composition of the technical grade lithium carbonate (crude lithium carbonate) selected in the following examples is only an example, and the actual applicable crude lithium carbonate raw material of the application is not limited thereto.

[0150] Example 1

[0151] This embodiment provides a lithium carbonate preparation device, including a stirring and washing system, a carbonization system, a filtration system, a neutralization system, a precipitation system, a drying and crushing system, a decomposition system, a purification system, a compression system, a purification system, an electrolysis system, a concentration system, a leaching system, and a lithium precursor system. The connection relationship of each part is as follows: Figure 1 and Figure 2 As shown. Among them:

[0152] The stirring and washing system may include a stirring and washing tank, a filter press and a slurry tank connected in sequence. The stirring and washing tank is used to stir and wash the crude lithium carbonate, which is then separated by the filter press to obtain crude lithium carbonate solid and stirring and washing liquid. The crude lithium carbonate solid is sent to the slurry tank to prepare slurry.

[0153] The carbonization system may include a carbonization tower for carbonizing the crude lithium carbonate to obtain a lithium bicarbonate solution.

[0154] The filtration system may include a filtration device for filtering the lithium bicarbonate solution after the carbonization reaction to obtain a filter residue and the filtered lithium bicarbonate solution.

[0155] The neutralization system may include a neutralization tank for providing the filtered lithium bicarbonate solution for a neutralization reaction.

[0156] The precipitation system may include a precipitation crystallizer for providing the lithium bicarbonate solution with a precipitation reaction to obtain refined lithium carbonate.

[0157] The drying and crushing system may include a centrifugal device, a drying device, a crushing device, an iron removal device and a packaging device connected in sequence, and is used for post-processing the lithium carbonate precipitate to obtain refined lithium carbonate.

[0158] The decomposition system may include a decomposition kettle for decomposing a mixed solution of sodium bicarbonate and lithium bicarbonate to obtain a gas product and a mixed solution of sodium carbonate and lithium carbonate, and using the mixed solution of sodium carbonate and lithium carbonate for a precipitation reaction.

[0159] The purification system may include a gas-liquid separator for purifying the gas product to obtain a lithium-containing solution and high-purity carbon dioxide.

[0160] The compression system may include a compressor for compressing high-purity carbon dioxide and then sending it into the carbonization system to be used as a reaction raw material for the carbonization reaction.

[0161] The purification system may include a purification device for purifying the washing liquid to obtain a mixed solution of sodium sulfate and lithium sulfate.

[0162] The electrolysis system may include an electrolytic cell for electrolyzing a mixed solution of sodium sulfate and lithium sulfate to obtain an alkaline solution and a sulfuric acid solution. The alkaline solution may be fed into a neutralization system for a neutralization reaction.

[0163] The concentration system may include a concentration device for concentrating the sulfuric acid solution and then sending it to the leaching system.

[0164] The leaching system may include a leaching tank for leaching the concentrated sulfuric acid solution with the filter residue to obtain a lithium-containing leachate, which may be fed into a precipitation system for precipitation reaction.

[0165] The premise lithium system may include a feed tank and an evaporation crystallization device. The premise lithium system is connected to the stirring and washing system to evaporate and crystallize part of the stirring and washing liquid to prepare sodium sulfate.

[0166] Example 2

[0167] This embodiment provides a method for preparing lithium carbonate, which uses lithium bicarbonate solution as a raw material to prepare battery-grade lithium carbonate (refined lithium carbonate), specifically comprising the following steps:

[0168] A mixed solution of sodium carbonate and lithium carbonate is added to a lithium bicarbonate solution (see Table 1 for ingredients) to obtain a precipitation solution. The precipitation solution is subjected to a precipitation reaction and centrifuged to obtain a lithium carbonate precipitate and a post-precipitation liquid. The post-precipitation liquid includes sodium bicarbonate and lithium bicarbonate. The lithium carbonate precipitate is further dried and crushed to obtain battery-grade lithium carbonate. Among them, in the mixed solution of sodium carbonate and lithium carbonate, the mass fraction of sodium carbonate is 22.6%, the mass fraction of lithium carbonate is 1.8%, and the mass fraction of lithium carbonate crystals is 0.33%. The addition rate of the mixed solution of sodium carbonate and lithium carbonate is 0.15m 3 / min, the molar ratio of sodium carbonate to lithium bicarbonate in the precipitation solution is 2.07:1, the precipitation reaction temperature is 46°C, the stirring speed of the precipitation reaction is 18 rpm, and the average particle size of the lithium carbonate precipitate is 100 μm.

[0169] The battery-grade lithium carbonate obtained in this example meets the requirements of Y / ST 582-2013 "Battery-Grade Lithium Carbonate." The obtained battery-grade lithium carbonate has a lithium carbonate content of 99.72%, a calcium content of 0.00032%, a magnesium content of 0.00027%, and a sodium content of 0.018%. The lithium recovery rate is 99.65%, and the product qualification rate is 99.9%.

[0170] Table 1. Composition of lithium bicarbonate solution used in this embodiment

[0171] Element <![CDATA[Li + ]]> <![CDATA[HCO3 - ]]> <![CDATA[Li2CO3]]> <![CDATA[Ca 2+ ]]> <![CDATA[Na 2+ ]]> <![CDATA[SO4 2- ]]> <![CDATA[Mg 2+ ]]> Moisture content / % 0.41 3.59 0.1 0.0021 0.15 0.42 0.0022 -95

[0172] Example 3

[0173] The difference from Example 2 is that in the mixed solution of sodium carbonate and lithium carbonate, the mass fraction of sodium carbonate is 23.2%, the mass fraction of lithium carbonate is 1.7%, and the mass fraction of lithium carbonate crystals is 0.25%. The addition rate of the mixed solution of sodium carbonate and lithium carbonate is 0.22m 3 / min, the molar ratio of sodium carbonate to lithium bicarbonate in the precipitation solution is 2.08:1, the precipitation reaction temperature is 65°C, the stirring speed of the precipitation reaction is 13 rpm, and the average particle size of the lithium carbonate precipitate is 185 μm.

[0174] The battery-grade lithium carbonate obtained in this example meets the requirements of Y / ST 582-2013 "Battery-Grade Lithium Carbonate." The obtained battery-grade lithium carbonate has a lithium carbonate content of 99.76%, a calcium content of 0.00029%, a magnesium content of 0.00026%, and a sodium content of 0.017%. The lithium recovery rate is 99.58%, and the product qualification rate is 99.8%.

[0175] Example 4

[0176] The difference from Example 2 is that in the mixed solution of sodium carbonate and lithium carbonate, the mass fraction of sodium carbonate is 23.9%, the mass fraction of lithium carbonate is 1.6%, and the mass fraction of lithium carbonate crystals is 0.2%. The addition rate of the mixed solution of sodium carbonate and lithium carbonate is 0.33m 3 / min, the precipitation reaction temperature was 87°C, the precipitation reaction stirring speed was 5 rpm, and the average particle size of the lithium carbonate precipitate was 300 μm.

[0177] The battery-grade lithium carbonate obtained in this example meets the requirements of Y / ST 582-2013 "Battery-Grade Lithium Carbonate." The obtained battery-grade lithium carbonate has a lithium carbonate content of 99.68%, a calcium content of 0.000334%, a magnesium content of 0.000285%, and a sodium content of 0.02%. The lithium recovery rate is 99.63%, and the product qualification rate is 99.75%.

[0178] Example 5

[0179] This embodiment provides a method for preparing lithium carbonate, which uses industrial-grade lithium carbonate (crude lithium carbonate) as a raw material to prepare refined lithium carbonate, specifically comprising the following steps:

[0180] 1) Slurrying: Industrial grade lithium carbonate (refer to Table 2 for ingredients) was added with water to prepare lithium carbonate slurry.

[0181] 2) Carbonization: A carbon dioxide feedstock is introduced into the lithium carbonate slurry for a carbonization reaction to convert the lithium carbonate slurry into a lithium bicarbonate solution. The carbonization reaction is performed at a pressure of 0.09 MPa, a temperature of 35° C., and a carbon dioxide volume fraction of 94.7% in the carbon dioxide feedstock.

[0182] 3) Filtration: The lithium bicarbonate solution is filtered through two-stage plate and frame filtration and one-stage ultrafiltration to obtain a filtered lithium bicarbonate solution and a filter residue containing insoluble impurities such as calcium and magnesium.

[0183] 4) Neutralization: A mixed solution of lithium hydroxide and sodium hydroxide was added to the filtered lithium bicarbonate solution to adjust the pH for a neutralization reaction, further removing impurities such as calcium and magnesium ions. The composition of the neutralized lithium bicarbonate solution is shown in Table 3. The total mass fraction of the mixed solution of lithium hydroxide and sodium hydroxide was 22%, the mass ratio of the mixed solution of lithium hydroxide and sodium hydroxide to the lithium bicarbonate solution was 0.05:1, and the pH of the neutralization reaction was 12.

[0184] 5) Precipitation: Add a mixed solution of sodium carbonate and lithium carbonate to the neutralized lithium bicarbonate solution to obtain a precipitation solution. The precipitation solution is subjected to precipitation reaction and centrifuged to obtain a lithium carbonate precipitate and a post-precipitation liquid. The post-precipitation liquid includes sodium bicarbonate and lithium bicarbonate. The lithium carbonate precipitate is further dried and crushed to obtain refined lithium carbonate. Among them, the mass fraction of sodium carbonate is 22.8%, the mass fraction of lithium carbonate is 1.65%, and the mass fraction of lithium carbonate crystals is 0.27%. The addition rate of the mixed solution of sodium carbonate and lithium carbonate is 0.19m 3 / min, the molar ratio of sodium carbonate to lithium bicarbonate in the precipitation solution is 2.07:1, the precipitation reaction temperature is 49°C, the stirring speed of the precipitation reaction is 11.3 rpm, and the average particle size of the lithium carbonate precipitate is 152 μm.

[0185] In this embodiment, the lithium carbonate content in the refined lithium carbonate obtained in step 5) is 99.79%, the calcium content is 0.00034%, the magnesium content is 0.000269%, the sodium content is 0.22%, the chlorine content is 0.0028%, the sulfate content is 0.078%, the lithium recovery rate is 99.52%, and the product qualification rate is 95%.

[0186] Table 2: Composition of industrial grade lithium carbonate used in this embodiment

[0187] Element <![CDATA[Li2CO3]]> Ca Co Ni Cl Na <![CDATA[SO4 2- ]]> Mg Moisture F content / % 98.7 0.1 0.001 0.002 0.003 0.15 0.53 0.006 -15 0.0009

[0188] In Table 2, the content of Li2CO3 is expressed on a dry basis, and the contents of the other components are expressed on a wet basis.

[0189] Table 3, the composition of the neutralized lithium bicarbonate solution obtained in this embodiment

[0190] Element <![CDATA[LiHCO3]]> <![CDATA[Li2CO3]]> Ca Na <![CDATA[SO4 2- ]]> Mg Moisture content / % 4 0.1 0.0035 0.05 0.18 0.0035 -95

[0191] Example 6

[0192] This embodiment provides a method for preparing lithium carbonate, which uses industrial-grade lithium carbonate (crude lithium carbonate) as a raw material to prepare refined lithium carbonate, specifically comprising the following steps:

[0193] 1) Stirring and washing: Water and the lithium bicarbonate solution obtained in the subsequent step were added to industrial-grade lithium carbonate (see Table 2 in Example 5 for its composition) and stirred and washed to obtain a washing liquid and a washing residue. The washing liquid was subjected to pre-impurity removal to allow soluble impurities to enter the washing liquid, thereby removing soluble impurities such as sodium sulfate and chloride ions. The washing liquid had a solids content of 40% and was stirred for 1.5 hours. The mass fraction of sulfate ions, sodium ions, and chloride ions in the washing residue after stirring and washing was 0.35%, 0.08%, and 0.002%, respectively. The lithium content in the washing liquid was 0.22%.

[0194] The stirred and washed slag is slurried to obtain lithium carbonate slurry with a solid content of 3.5%.

[0195] 2) Carbonization: A carbon dioxide feedstock is introduced into the lithium carbonate slurry for a carbonization reaction to convert the lithium carbonate slurry into a lithium bicarbonate solution. The carbonization reaction is performed at a pressure of 0.09 MPa, a temperature of 33°C, and a carbon dioxide volume fraction of 94.7% in the carbon dioxide feedstock.

[0196] 3) Filtration: The lithium bicarbonate solution is filtered through two-stage plate and frame filtration and one-stage ultrafiltration to obtain a filtered lithium bicarbonate solution and a filter residue containing insoluble impurities such as calcium and magnesium.

[0197] 4) Neutralization: A mixed solution of lithium hydroxide and sodium hydroxide was added to the filtered lithium bicarbonate solution to adjust the pH for a neutralization reaction, and further precipitation was performed to remove impurities such as calcium and magnesium ions. The composition of the neutralized lithium bicarbonate solution is shown in Table 4. The total mass fraction of the mixed solution of lithium hydroxide and sodium hydroxide was 22%, the mass ratio of the mixed solution of lithium hydroxide and sodium hydroxide to the lithium bicarbonate solution was 0.05:1, and the pH value of the neutralization reaction was 12.

[0198] 5) Precipitation: Add a mixed solution of sodium carbonate and lithium carbonate to the neutralized lithium bicarbonate solution to obtain a precipitation solution. The precipitation solution is subjected to precipitation reaction and centrifuged to obtain a lithium carbonate precipitate and a post-precipitation liquid. The post-precipitation liquid includes sodium bicarbonate and lithium bicarbonate. The lithium carbonate precipitate is further dried and crushed to obtain battery-grade lithium carbonate. Among them, in the mixed solution of sodium carbonate and lithium carbonate, the mass fraction of sodium carbonate is 22.8%, the mass fraction of lithium carbonate is 1.65%, and the mass fraction of lithium carbonate crystals is 0.27%. The addition rate of the mixed solution of sodium carbonate and lithium carbonate is 0.19m 3 / min, the molar ratio of sodium carbonate to lithium bicarbonate in the precipitation solution is 2.07:1, the precipitation reaction temperature is 49°C, the stirring speed of the precipitation reaction is 11.3 rpm, and the average particle size of the lithium carbonate precipitate is 152 μm.

[0199] In this embodiment, battery-grade lithium carbonate is obtained in step 5), which meets the requirements of Y / ST 582-2013 "Battery-Grade Lithium Carbonate". The obtained battery-grade lithium carbonate has a lithium carbonate content of 99.60%, a calcium content of 0.000243, a magnesium content of 0.000197, a sodium content of 0.014%, a chlorine content of 0.0014%, and a sulfate content of 0.034%. The lithium recovery rate is 99.41%, and the product qualification rate is 99.9%.

[0200] Table 4: Composition of the neutralized lithium bicarbonate solution obtained in this embodiment

[0201] Element <![CDATA[LiHCO3]]> <![CDATA[Li2CO3]]> Ca Na <![CDATA[SO4 2- ]]> Mg Moisture content / % 4 0.098 0.001 0.01 0.092 0.001 -95

[0202] Example 7

[0203] This embodiment provides a method for preparing lithium carbonate, using industrial-grade lithium carbonate (crude lithium carbonate) as a raw material to prepare battery-grade lithium carbonate (refined lithium carbonate). Unlike Example 6, this embodiment also includes purification and electrolysis of the washing liquid, specifically comprising the following steps:

[0204] 1) Stirring and washing: Water and the lithium bicarbonate solution obtained in the subsequent step were added to industrial-grade lithium carbonate (see Table 2 in Example 5 for its composition) and stirred and washed to obtain a washing liquid and a washing residue. The washing liquid was subjected to pre-impurity removal to allow soluble impurities to enter the washing liquid, thereby removing soluble impurities such as sodium sulfate and chloride ions. The washing liquid had a solids content of 40% and was stirred for 1.5 hours. The mass fraction of sulfate ions, sodium ions, and chloride ions in the washing residue after stirring and washing was 0.35%, 0.08%, and 0.002%, respectively. The lithium content in the washing liquid was 0.22%.

[0205] The stirred and washed slag is slurried to obtain lithium carbonate slurry with a solid content of 3.5%.

[0206] 2) Carbonization: A carbon dioxide feedstock is introduced into the lithium carbonate slurry for a carbonization reaction to convert the lithium carbonate slurry into a lithium bicarbonate solution. The carbonization reaction is performed at a pressure of 0.09 MPa, a temperature of 33°C, and a carbon dioxide volume fraction of 94.7% in the carbon dioxide feedstock.

[0207] 3) Filtration: The lithium bicarbonate solution is filtered through two-stage plate and frame filtration and one-stage ultrafiltration to obtain a filtered lithium bicarbonate solution and a filter residue containing insoluble impurities such as calcium and magnesium.

[0208] 4) Neutralization: A mixed solution of lithium hydroxide and sodium hydroxide was added to the filtered lithium bicarbonate solution to adjust the pH for neutralization. Impurities such as calcium and magnesium ions were further removed by precipitation. The composition of the neutralized lithium bicarbonate solution is shown in Table 5. The total mass fraction of the mixed solution of lithium hydroxide and sodium hydroxide was 22%, the mass ratio of the mixed solution of lithium hydroxide and sodium hydroxide to the lithium bicarbonate solution was 0.05:1, and the pH of the neutralization reaction was 12.

[0209] 5) Precipitation: Add a mixed solution of sodium carbonate and lithium carbonate to the neutralized lithium bicarbonate solution to obtain a precipitation solution. The precipitation solution is subjected to precipitation reaction and centrifuged to obtain a lithium carbonate precipitate and a post-precipitation liquid. The post-precipitation liquid includes sodium bicarbonate and lithium bicarbonate. The lithium carbonate precipitate is further dried and crushed to obtain battery-grade lithium carbonate. Among them, in the mixed solution of sodium carbonate and lithium carbonate, the mass fraction of sodium carbonate is 22.8%, the mass fraction of lithium carbonate is 1.65%, and the mass fraction of lithium carbonate crystals is 0.27%. The addition rate of the mixed solution of sodium carbonate and lithium carbonate is 0.19m 3 / min, the molar ratio of sodium carbonate to lithium bicarbonate in the precipitation solution is 2.07:1, the precipitation reaction temperature is 49°C, the stirring speed of the precipitation reaction is 11.3 rpm, and the average particle size of the lithium carbonate precipitate is 152 μm.

[0210] 6) Purification: Take part of the stirred and washed liquid and perform multi-stage impurity removal, precipitation and chelating resin purification to obtain Ca 2+ and Mg 2+ The mixed solution of sodium sulfate and lithium sulfate with a total concentration of less than 0.0015% is used for the electrolysis reaction in step 7). The mixed solution accounts for 50% of the total amount of the washing solution.

[0211] 7) Electrolysis: The purified mixed solution of sodium sulfate and lithium sulfate is electrolyzed to obtain a mixed solution of sodium hydroxide and lithium hydroxide and a dilute sulfuric acid solution. The dilute sulfuric acid solution is concentrated to a mass fraction of 37% and then sent to step 8) for leaching. The mixed solution of sodium hydroxide and lithium hydroxide is sent to step 4) for adjusting the pH value of the neutralization reaction to precipitate and remove impurities. The electrolysis voltage of the electrolysis reaction is 4.0V and the electrolysis current is 0.3A / cm 2 .

[0212] The preparation method of lithium carbonate provided in this embodiment also includes:

[0213] 8) Leaching: The concentrated dilute sulfuric acid is mixed with the filter residue obtained by filtration in step 3) for leaching to obtain a lithium-containing leachate and an insoluble leachate residue. The sulfuric acid leaching can convert the lithium carbonate in the filter residue after filtration and impurity removal in step 3) into lithium sulfate, obtaining a lithium-containing leachate containing lithium carbonate. The lithium-containing leachate is then fed to step 5) to be mixed with a precipitation solution for precipitation reaction, thereby further recovering lithium from the lithium-containing leachate. The mass ratio of the lithium-containing leachate to the precipitation solution is 0.01:1.

[0214] In this embodiment, battery-grade lithium carbonate is obtained in step 5), which meets the requirements of Y / ST 582-2013 "Battery-Grade Lithium Carbonate". The obtained battery-grade lithium carbonate has a lithium carbonate content of 99.62%, a calcium content of 0.00038%, a magnesium content of 0.000285%, a sodium content of 0.021%, a chlorine content of 0.0019%, and a sulfate content of 0.032%. The lithium recovery rate is 99.44%, and the product qualification rate is 99.93%.

[0215] Table 5: Composition of the neutralized lithium bicarbonate solution obtained in this embodiment

[0216] Element <![CDATA[LiHCO3]]> <![CDATA[Li2CO3]]> Ca Na <![CDATA[SO4 2- ]]> Mg Moisture content / % 4.1 0.1 0.0035 0.008 0.1 0.0035 -95

[0217] Example 8

[0218] This embodiment provides a method for preparing lithium carbonate, which is implemented based on the preparation device in Example 1. The preparation method in this embodiment uses industrial-grade lithium carbonate (crude lithium carbonate) as a raw material to prepare battery-grade lithium carbonate (refined lithium carbonate), and specifically includes the following steps:

[0219] 1) Stirring and washing: Add water and the lithium bicarbonate solution obtained in the subsequent step to industrial-grade lithium carbonate (see Table 4 in Example 5 for ingredients) and dissolve and stir to obtain a washing liquid and a washing residue. Stirring and washing pre-impurities allow soluble impurities to enter the washing liquid, thereby removing soluble impurities such as sodium sulfate and chloride ions. The solid content of the washing liquid is 40%, and the stirring time is 1.5 hours. The mass fraction of sulfate ions in the washing residue after stirring and washing is 0.35%, the mass fraction of sodium ions is 0.08%, and the mass fraction of chloride ions is 0.002%. The lithium content in the washing liquid is 0.22%.

[0220] The stirred and washed slag is slurried to obtain lithium carbonate slurry with a solid content of 3.5%.

[0221] 2) Carbonization: A carbon dioxide feedstock is introduced into the lithium carbonate slurry for a carbonization reaction to convert the lithium carbonate slurry into a lithium bicarbonate solution. The carbonization reaction is performed at a pressure of 0.09 MPa, a temperature of 33°C, and a carbon dioxide volume fraction of 94.7% in the carbon dioxide feedstock.

[0222] 3) Filtration: The lithium bicarbonate solution is filtered through two-stage plate and frame filtration and one-stage ultrafiltration to obtain a filtered lithium bicarbonate solution and a filter residue containing insoluble impurities such as calcium and magnesium.

[0223] 4) Neutralization: A mixed solution of lithium hydroxide and sodium hydroxide was added to the filtered lithium bicarbonate solution to adjust the pH for neutralization. Impurities such as calcium and magnesium ions were further precipitated to remove them. The composition of the neutralized lithium bicarbonate solution is shown in Table 6. The total mass fraction of the mixed solution of lithium hydroxide and sodium hydroxide was 22%, the mass ratio of the mixed solution of lithium hydroxide and sodium hydroxide to the lithium bicarbonate solution was 0.05:1, and the pH of the neutralization reaction was 12.

[0224] 5) Precipitation: Add a mixed solution of sodium carbonate and lithium carbonate to the neutralized lithium bicarbonate solution to obtain a precipitation solution. The precipitation solution is subjected to precipitation reaction and centrifuged to obtain a lithium carbonate precipitate and a post-precipitation liquid. The post-precipitation liquid includes sodium bicarbonate and lithium bicarbonate. The lithium carbonate precipitate is further dried and crushed to obtain battery-grade lithium carbonate. Among them, in the mixed solution of sodium carbonate and lithium carbonate, the mass fraction of sodium carbonate is 22.8%, the mass fraction of lithium carbonate is 1.65%, and the mass fraction of lithium carbonate crystals is 0.27%. The addition rate of the mixed solution of sodium carbonate and lithium carbonate is 0.19m 3 / min, the molar ratio of sodium carbonate to lithium bicarbonate in the precipitation solution is 2.07:1, the precipitation reaction temperature is 49°C, the stirring speed of the precipitation reaction is 11.3 rpm, and the average particle size of the lithium carbonate precipitate is 152 μm.

[0225] 6) Decomposition: The precipitated liquid is evaporated and decomposed to produce a gaseous product and a mixed solution of sodium carbonate and lithium carbonate. The mixed solution of sodium carbonate and lithium carbonate is recycled for the precipitation reaction. The evaporation and decomposition temperature is 220°C, the evaporation and decomposition time is 1.8 hours, and the volume fraction of carbon dioxide in the gaseous product is 60%.

[0226] 7) Carbon dioxide recycling: The gas product is further cooled to remove liquid and adsorbed to remove H2S / HCl / HF, etc. to obtain a lithium-containing solution and high-purity carbon dioxide with a volume fraction of 94%. The high-purity carbon dioxide is recycled to the carbonization reaction, and the lithium-containing solution is used as a reaction raw material for the neutralization reaction to recover lithium.

[0227] 8) Purification: Take part of the stirred and washed liquid and perform multi-stage impurity removal, precipitation and chelating resin purification to obtain Ca 2+ and Mg 2+The mixed solution of sodium sulfate and lithium sulfate with a total concentration of less than 0.0015% is used for the electrolysis reaction in step 9). The stirred washing liquid accounts for 50% of the total stirred washing liquid.

[0228] 9) Electrolysis: The purified mixed solution of sodium sulfate and lithium sulfate is subjected to an electrolytic reaction to obtain a mixed solution of sodium hydroxide and lithium hydroxide and a dilute sulfuric acid solution. The dilute sulfuric acid solution is concentrated to a mass fraction of 37% and then sent to step 10) for leaching. The mixed solution of sodium hydroxide and lithium hydroxide is sent to step 4) for adjusting the pH value of the neutralization reaction, thereby precipitating and removing impurities. The electrolysis voltage of the electrolysis reaction is 4.0V and the electrolysis current is 0.3A / cm 2 .

[0229] 10) Leaching: The concentrated dilute sulfuric acid is mixed with the filter residue obtained by filtration in step 3) for leaching to obtain a lithium-containing leachate and an insoluble leachate residue. The sulfuric acid leaching can convert the lithium carbonate in the filter residue after filtration and impurity removal in step 3) into lithium sulfate, thereby obtaining a lithium-containing leachate containing lithium carbonate. The lithium-containing leachate is then fed to step 5) to be mixed with a precipitation solution for precipitation reaction, thereby further recovering lithium from the lithium-containing leachate. The mass ratio of the lithium-containing leachate to the precipitation solution is 0.01:1.

[0230] In this embodiment, battery-grade lithium carbonate is obtained in step 5), which meets the requirements of Y / ST 582-2013 "Battery-Grade Lithium Carbonate". The obtained battery-grade lithium carbonate has a lithium carbonate content of 99.66%, a calcium content of 0.000256%, a magnesium content of 0.000211%, a sodium content of 0.015%, a chlorine content of 0.0012%, and a sulfate content of 0.026%. The lithium recovery rate is 99.55%, and the product qualification rate is 99.96%.

[0231] Table 6: Composition of the neutralized lithium bicarbonate solution obtained in this embodiment

[0232] Element <![CDATA[LiHCO3]]> <![CDATA[Li2CO3]]> Ca Na <![CDATA[SO4 2- ]]> Mg Moisture content / % 4.06 0.045 0.0008 0.006 0.087 0.0008 -95

[0233] Comparative Example 1

[0234] The difference from Example 8 is that the temperature of the precipitation reaction in step 5) is 92° C. and the stirring speed is 55 rpm.

[0235] The lithium carbonate product obtained has a lithium carbonate content of 99.53%, a calcium ion content of 0.003%, a magnesium ion content of 0.00034%, a sodium ion content of 0.022%, a lithium recovery rate of 99.15%, and a product qualification rate of 98.6%.

[0236] Comparative Example 2

[0237] The difference from Example 6 is that after step 4) "neutralization", the following process is carried out:

[0238] Resin impurity removal: The neutralized lithium bicarbonate solution is adjusted to a pH of 11 and then passed through an ion exchange resin column to adsorb divalent and higher cations in the lithium bicarbonate solution, producing a lithium-containing purified solution for the next step. The resin exchange column is then replaced with deionized water, followed by acid washing with dilute acid and then alkaline washing with sodium hydroxide solution to regenerate the resin.

[0239] The lithium-containing purified liquid obtained by removing impurities from the resin is further dried and pulverized to produce battery-grade lithium carbonate. The resulting lithium carbonate product contains 99.65% lithium carbonate, 0.0003% calcium, 0.00025% magnesium, and 0.013% sodium. The lithium recovery rate is 98.29%, and the product qualification rate is 99.95%.

[0240] Table 7. Comparison of the main technical effects of Examples 2-8 and Comparative Examples 1-2

[0241]

[0242] In Table 7, the amount of carbon dioxide replenished refers to the consumption of the carbon dioxide raw material in the carbonization step; the lithium recovery rate = the mass of lithium in the lithium carbonate product / the mass of lithium in the crude lithium carbonate; the product qualification rate = the amount of lithium carbonate product that meets the requirements of Y / ST 582-2013 "Battery Grade Lithium Carbonate" / the total amount of lithium carbonate product.

[0243] Combined with the data in Tables 1-7 regarding the above embodiments and comparative examples, it can be seen that after the refined lithium carbonate product is prepared by the preparation method provided by the present application, the lithium recovery rate can reach more than 99.4%, while the calcium content is less than 0.0004%, and the magnesium content is less than 0.0003%. It can be seen that the present application can not only improve the lithium recovery rate, but also effectively remove impurities such as calcium and magnesium, thereby achieving the preparation of a lithium carbonate product with higher purity.

[0244] Specifically, Examples 2-4 demonstrate that by controlling precipitation reaction conditions such as temperature, stirring speed, and lithium carbonate precipitate particle size, refined lithium carbonate can be prepared from a lithium bicarbonate solution while effectively removing calcium, magnesium, and sodium ion impurities from the lithium bicarbonate solution. The resulting refined lithium carbonate meets the requirements for battery-grade sulfate and can be directly used as a raw material for lithium-ion battery production, contributing to the development of the lithium-ion battery industry.

[0245] It can be seen from Examples 5-8 that, compared with Example 5, the crude lithium carbonate is first stirred and washed in Examples 6-7, and the corresponding contents of soluble impurities such as sodium, chlorine, and sulfate in the products obtained in Examples 6-7 are lower than those in Example 5. It can be seen that the stirring and washing means in the examples of the present application can remove some soluble impurities such as sodium, chlorine, and sulfate, and can ensure that the lithium carbonate content and lithium recovery rate in the obtained product are at a high level.

[0246] Compared with Example 6, the washing liquid is electrolyzed in Example 7. Accordingly, the lithium carbonate content and lithium recovery rate in the product obtained in Example 7 are higher than those in Example 6. It can be seen that the lithium in the washing liquid can be effectively recovered by the electrolysis method in the embodiment of the present application.

[0247] Compared with Example 7, in Example 8, the liquid after precipitation is decomposed to obtain carbon dioxide, sodium carbonate and lithium carbonate. The carbon dioxide is recycled for the carbonization reaction, and the sodium carbonate and lithium carbonate are recycled for the precipitation reaction, thereby reducing the amount of carbon dioxide supplement and the consumption of sodium carbonate and lithium carbonate raw materials, reducing material consumption, and lowering production costs.

[0248] Comparing the experimental data of Comparative Example 1 with that of Example 8, in Comparative Example 1, the precipitation reaction temperature and stirring speed were changed. The calcium and magnesium impurity contents in the obtained product were 0.003% and 0.0034%, respectively, which were much higher than the calcium and magnesium impurity contents of 0.000256% and 0.000211% in the product obtained in Example 8. In addition, the qualified rate of the product obtained in Comparative Example 1 was significantly lower than that in Example 8. It can be seen that only under the precipitation reaction conditions in the examples of the present application can the calcium and magnesium impurities be effectively removed and a lithium carbonate product with a high qualified rate be obtained.

[0249] Comparing the experimental data of Comparative Example 2 with that of Example 6, in Comparative Example 2, the resin impurity removal process was used, and the calcium and magnesium impurity contents in the obtained product were 0.0003% and 0.00025%, respectively, which were higher than the calcium and magnesium impurity contents of 0.000243% and 0.000197% in the product obtained in Example 6. In addition, the lithium recovery rate of Comparative Example 2 was 98.29%, which was lower than the lithium recovery rate of 99.41% in Example 6. It can be seen that the precipitation reaction impurity removal process used in the examples of the present application can effectively remove calcium and magnesium impurities and fully recover lithium from the crude lithium carbonate. Moreover, compared with the resin impurity removal method, the examples of the present application can significantly reduce the amount of wastewater generated, which is conducive to industrial production.

[0250] The various technical features described above can be combined arbitrarily. Although not all possible combinations of these technical features are described, any combination of these technical features should be considered to be covered by this specification as long as such combination does not conflict.

[0251] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing lithium carbonate, characterized in that: The following steps are involved: Obtaining a lithium bicarbonate solution, wherein the total concentration of calcium and magnesium ions in the lithium bicarbonate solution is 0.0005%-0.007%; adding a mixed solution of sodium carbonate and lithium carbonate to the lithium bicarbonate solution to obtain a precipitation solution, subjecting the precipitation solution to a precipitation reaction to obtain a lithium carbonate precipitate and a post-precipitation liquid, wherein the post-precipitation liquid comprises sodium bicarbonate and lithium bicarbonate, and post-treating the lithium carbonate precipitate to obtain refined lithium carbonate; In the mixed solution of sodium carbonate and lithium carbonate, the mass fraction of sodium carbonate is 21-25%, and the mass fraction of lithium carbonate is 1.5-2%; The precipitation reaction temperature is 46-87° C.; the precipitation reaction is carried out under stirring at a stirring speed of 5-18 rpm.

2. The method for preparing lithium carbonate according to claim 1, wherein In the mixed solution of sodium carbonate and lithium carbonate, the mass fraction of lithium carbonate crystals is 0.2-0.6%.

3. The method for preparing lithium carbonate according to claim 1, wherein The molar ratio of sodium carbonate to lithium bicarbonate in the precipitation solution is 2.05-2.15:

1.

4. The method for preparing lithium carbonate according to claim 1, wherein The average particle size of the lithium carbonate precipitate is 100-300 μm.

5. The method for preparing lithium carbonate according to claim 1, wherein The total concentration of calcium and magnesium ions in the refined lithium carbonate is ≤0.001%.

6. The method for preparing lithium carbonate according to claim 1, wherein The total concentration of calcium and magnesium ions in the lithium bicarbonate solution is 0.001%-0.007%.

7. The method for preparing lithium carbonate according to claim 1, wherein The preparation method further comprises: The crude lithium carbonate and the carbon dioxide raw material are subjected to carbonization reaction to obtain the lithium bicarbonate solution.

8. The method for preparing lithium carbonate according to claim 7, wherein The pressure of the carbonization reaction is 0.02-0.2 MPa.

9. The method for preparing lithium carbonate according to claim 7, wherein The temperature of the carbonization reaction is 30-55°C.

10. The method for preparing lithium carbonate according to claim 7, wherein The volume fraction of carbon dioxide in the carbon dioxide raw material is 80-99%.

11. The method for preparing lithium carbonate according to claim 7, wherein Before the crude lithium carbonate is subjected to carbonization reaction with the carbon dioxide raw material, the preparation method further comprises: The crude lithium carbonate is stirred and washed to obtain a stirring liquid and a stirring residue, the stirring residue is pulped to obtain a slurry, and the slurry is subjected to the carbonization reaction with a carbon dioxide raw material to obtain the lithium bicarbonate solution.

12. The method for preparing lithium carbonate according to claim 11, wherein The stirring and washing time is 0.5-1.5h.

13. The method for preparing lithium carbonate according to claim 11, wherein The solid content of the agitation and washing liquid is 30-40%.

14. The method for preparing lithium carbonate according to claim 11, wherein The mass fraction of sulfate in the stirred and washed residue is ≤0.45%, and the mass fraction of sodium ions is ≤0.3%.

15. The method for preparing lithium carbonate according to claim 11, wherein The solid content of the slurry is 4.5-6%.

16. The method for preparing lithium carbonate according to claim 11, wherein Before subjecting the lithium bicarbonate solution to a precipitation reaction, the preparation method further comprises: The lithium bicarbonate solution is filtered to obtain a filter residue and a filtered lithium bicarbonate solution, and the filtered lithium bicarbonate solution is subjected to a precipitation reaction.

17. The method for preparing lithium carbonate according to claim 16, wherein: Before subjecting the lithium bicarbonate solution to a precipitation reaction, the preparation method further comprises: A neutralizing agent is added to the lithium bicarbonate solution to carry out a neutralization reaction, and then a precipitation reaction is carried out.

18. The method for preparing lithium carbonate according to claim 17, wherein: The neutralizing agent includes lithium hydroxide and / or sodium hydroxide solution.

19. The method for preparing lithium carbonate according to claim 18, wherein: The mass fraction of the lithium hydroxide and / or sodium hydroxide solution is 12-25%.

20. The method for preparing lithium carbonate according to claim 18, wherein: The mass ratio of the lithium hydroxide and / or sodium hydroxide solution to the lithium bicarbonate solution is 0.02-0.09:

1.

21. The method for preparing lithium carbonate according to claim 17, wherein: The pH value of the neutralization reaction is 11.5-12.

5.

22. The method for preparing lithium carbonate according to claim 16, wherein: The preparation method further comprises: Purifying the washing liquid to obtain a mixed solution of sodium sulfate and lithium sulfate; electrolyzing the mixed solution of sodium sulfate and lithium sulfate to obtain an alkaline solution and a sulfuric acid solution; Leaching the sulfuric acid solution and the filter residue to obtain a lithium-containing leachate; The lithium-containing leachate is mixed with the precipitation solution to perform a precipitation reaction.

23. The method for preparing lithium carbonate according to claim 22, wherein: The mass fraction of the sulfuric acid solution is 25-45%.

24. The method for preparing lithium carbonate according to claim 22, wherein: The mass ratio of the lithium-containing leachate to the precipitation solution is 0.005-0.03:

1.

25. The method for preparing lithium carbonate according to claim 22, wherein: The mass of the agitation and washing liquid participating in the electrolysis reaction accounts for 28-67% of the total mass of the agitation and washing liquid.

26. The method for preparing lithium carbonate according to claim 17, wherein: The preparation method further comprises: Purifying the washing liquid to obtain a mixed solution of sodium sulfate and lithium sulfate; electrolyzing the mixed solution of sodium sulfate and lithium sulfate to obtain an alkaline solution and a sulfuric acid solution; The alkali solution is used as the neutralizing agent for the neutralization reaction.

27. The method for preparing lithium carbonate according to claim 26, wherein: The alkali solution includes sodium hydroxide and / or lithium hydroxide solution.

28. The method for preparing lithium carbonate according to claim 26, wherein: The mass of the agitation and washing liquid participating in the electrolysis reaction accounts for 28-67% of the total mass of the agitation and washing liquid.

29. The method for preparing lithium carbonate according to claim 26, wherein: The preparation method further comprises: performing a decomposition reaction on the post-precipitation liquid to obtain a gas product and a mixed solution of sodium carbonate and lithium carbonate, and using the mixed solution of sodium carbonate and lithium carbonate for the precipitation reaction.

30. The method for preparing lithium carbonate according to claim 29, wherein: The temperature of the decomposition reaction is 165-248°C.

31. The method for preparing lithium carbonate according to claim 29, wherein The decomposition reaction time is 0.6-3h.

32. The method for preparing lithium carbonate according to claim 29, wherein The volume fraction of carbon dioxide in the gas product is 45-85%.

33. The method for preparing lithium carbonate according to claim 29, wherein The gas product is purified to obtain a lithium-containing solution and high-purity carbon dioxide, which is used as a carbon dioxide raw material for the carbonization reaction. The volume fraction of carbon dioxide in the high-purity carbon dioxide is 80-99%.

34. The method for preparing lithium carbonate according to claim 33, wherein Before subjecting the lithium bicarbonate solution to a precipitation reaction, the preparation method further comprises: adding a neutralizing agent to the lithium bicarbonate solution to carry out a neutralization reaction, and then carrying out a precipitation reaction; The lithium-containing solution is used as a reaction raw material for the neutralization reaction.

35. The method for preparing lithium carbonate according to claim 1, wherein The addition rate of the mixed solution of sodium carbonate and lithium carbonate is 0.15-0.4m 3 / min.

36. A lithium carbonate preparation device, characterized in that: The invention comprises a carbonization system and a precipitation system which are connected in sequence. The carbonization system is used for carbonizing crude lithium carbonate to obtain a lithium bicarbonate solution; and the precipitation system is used for precipitating the lithium bicarbonate solution to obtain refined lithium carbonate.

37. The lithium carbonate production device according to claim 36, characterized in that: It also includes a filtration system, and the carbonization system, the filtration system and the precipitation system are connected in sequence.

38. The lithium carbonate production device according to claim 36 or 37, characterized in that: It also includes a neutralization system, and the carbonization system, the neutralization system and the precipitation system are connected in sequence.

39. The lithium carbonate production device according to claim 37, characterized in that: It also includes a stirring and washing system, a purification system, an electrolysis system and a leaching system. The stirring and washing system, the carbonization system, the filtration system and the precipitation system are connected in sequence, and the stirring and washing system, the purification system, the electrolysis system, the leaching system and the precipitation system are connected in sequence, and the filtration system is connected to the leaching system.

40. The lithium carbonate production device according to claim 38, characterized in that: It also includes a stirring and washing system, a purification system and an electrolysis system. The stirring and washing system, the carbonization system, the neutralization system and the precipitation system are connected in sequence, and the stirring and washing system, the purification system, the electrolysis system and the neutralization system are connected in sequence.

41. The lithium carbonate production device according to claim 36, characterized in that: It also includes a decomposition system, which is connected to the precipitation system and the carbonization system respectively.

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