Preparation method and application of high-purity brine lithium carbonate

Abstract

The invention discloses a preparation method and application of high-purity brine lithium carbonate. According to the method, the purity bottleneck of salt lake lithium extraction is broken through, industrial sodium carbonate is replaced with ammonia gas and carbon dioxide, and introduction of exogenous impurities is eradicated from the source; by combining dynamic pH regulation and high-temperature ionized water washing, co-precipitation and adsorption of sodium and other impurities are effectively inhibited, so that the purity of a lithium carbonate product stably reaches 99.9% or above, the requirement of a high-end lithium battery is met, and the additional value is remarkably improved. According to the process, the system is spontaneously heated to 90 DEG C or above by utilizing ammonia gas dissolution heat release, so that rapid decomposition of an intermediate product lithium bicarbonate is promoted, and the reaction rate is increased. Under the condition, the material liquid does not need to be greatly diluted to keep the purity, and the single precipitation conversion rate of the lithium is greatly improved to 91-96% and is obviously superior to the level of about 85% in the traditional process. Carbon dioxide is used as a carbon source, process conditions are mild, high-pressure equipment is not needed, follow-up separation and wastewater treatment processes are simplified, and the method has the advantages of greenness, low carbon and high industrial feasibility.

Description

Technical Field

[0001] This invention relates to the field of inorganic chemical and new energy materials technology, specifically to a method for preparing high-purity brine lithium carbonate and its application. Background Technology

[0002] Lithium carbonate is a key raw material for lithium-ion battery cathode materials. Its chemical purity, especially the content of impurities such as sodium, calcium, magnesium, and boron, is a decisive factor affecting battery energy density, cycle life, and safety reliability. Against the backdrop of the rapid development of the global electric vehicle and energy storage industries, the market demand for high-purity lithium carbonate with a purity of no less than 99.9% (i.e., Li₂CO₃-O₃ grade) is increasingly urgent. my country has abundant lithium reserves in salt lakes, and lithium extraction from salt lakes has become an important pillar of the domestic lithium resource supply system, accounting for nearly one-third of the national total production.

[0003] Currently, the mainstream industrial-scale extraction technology for lithium from salt lakes is the membrane separation-adsorption coupling method. This process obtains a lithium chloride solution through adsorption enrichment and membrane purification, and finally prepares lithium carbonate by introducing industrial sodium carbonate for precipitation. However, this traditional process has two inherent drawbacks that are difficult to overcome: First, there is the bottleneck of product purity. Due to the properties of the precipitant itself, the final product purity is usually difficult to consistently exceed 99.6% (battery-grade standard). The sources of impurities mainly include two aspects: one is the inherent impurities such as calcium, magnesium, and boron introduced exogenously by industrial sodium carbonate; the other is the competitive co-precipitation or surface coating of sodium ions present in the reaction system with the target lithium ions, leading to excessive sodium content in the product. These two factors together restrict the improvement of the product to a high purity level of 99.9% or higher.

[0004] Secondly, there is a conflict between production efficiency and resource utilization. To suppress the aforementioned co-precipitation phenomenon and maintain the basic purity of the product, industrial production commonly employs a method of significantly diluting the reaction system. This conservative strategy directly results in a significantly low single-precipitation conversion rate of lithium ions, typically only around 85%, leading to a phased loss of lithium resources and an increase in the amount of mother liquor to be processed. Although lithium in the mother liquor can be recovered through subsequent extraction processes, this leads to a longer process flow, increased consumption of auxiliary chemicals, and a heavier wastewater treatment load, thereby increasing overall production costs and environmental pressure.

[0005] To avoid introducing impurities such as sodium at the source and to practice green manufacturing, the use of carbon dioxide instead of sodium carbonate as a precipitant has become a research hotspot. For example, US Patent 20120237419A1 discloses a method for precipitating lithium carbonate by passing carbon dioxide into a lithium chloride solution using ammonia as a medium. The core of this invention lies in solving the problem of raw material transportation costs in specific geographical environments (such as high-altitude salt lake areas). Its focus is on constructing an on-site production and recycling system that obtains carbon dioxide by calcining local limestone and regenerates ammonia through the reaction of by-product ammonium chloride with lime, thereby achieving the goal of economical production.

[0006] However, if measured against the standard of industrially stable production of high-purity, high-yield lithium carbonate, this existing approach has significant technical limitations: (1) The reaction process control is relatively crude. It only outlines the basic steps of mixing ammonia and carbon dioxide with the feed liquid, without precisely controlling the key parameters that determine precipitation kinetics and product purity.

[0007] (2) Lithium bicarbonate, as a key intermediate in the carbonization reaction, decomposes rapidly into lithium carbonate at higher temperatures (usually above 80°C). This is an important way to improve the reaction rate and final conversion rate, but this existing technology does not take this into consideration.

[0008] (3) The purification process is relatively complex. It uses a high-concentration lithium carbonate saturated solution for displacement washing. This method not only increases the operation steps and material management costs, but also may face the risk of impurity accumulation due to the recycling of the washing solution during long-term operation.

[0009] (4) Using simulated brine or concentrated brine, it was not fully verified whether the method could maintain the same excellent purity and yield performance when facing raw materials with common low to medium lithium concentrations and containing a variety of high concentrations of impurity ions (such as sodium, boron, magnesium, and calcium) in actual industrial production.

[0010] In summary, existing technologies for preparing high-purity lithium carbonate are either limited by the inherent contradictions of traditional processes or focus only on solving economic issues in emerging gas carbonization routes, lacking a complete and industrially feasible technical solution that can simultaneously achieve ultra-high product purity and high production conversion rate through precise process control for complex industrial feed solutions. Summary of the Invention

[0011] Based on the above-mentioned technical problems, this invention improves the process of lithium extraction from salt lake brine to prepare lithium carbonate. Without introducing foreign impurities, it maximizes the conversion of qualified lithium solution refined by membrane separation-adsorption coupling method into lithium carbonate. This method aims to inherit the advantages of gas carbonation method, which is green and low-carbon and has no external impurities. Through innovative process flow design, it focuses on solving the key control problems in the reaction process, thereby achieving stable and efficient preparation of high-purity lithium carbonate.

[0012] This invention protects a method for preparing high-purity lithium carbonate brine, specifically comprising the following steps: Step 1, Preparation of ammonia-lithium water: Under heat preservation conditions, ammonia gas is introduced into a qualified lithium solution at a certain temperature until saturation is achieved to obtain ammonia-lithium water; The principle behind the above steps is that ammonia gas is introduced into the qualified lithium solution until saturation under heat preservation conditions. The ammonia gas quickly dissolves in water to form ammonia monohydrate, and partially ionizes into NH4⁺ and OH⁻, forming an alkaline solution. On the one hand, this provides the alkaline medium required for subsequent carbon dioxide absorption, and on the other hand, the ammonia dissolution process is an exothermic reaction, which helps to start and maintain the initial reaction temperature of the system. Ammonia forms a soluble complex with lithium ions, which helps to stabilize lithium in the solution.

[0013] Step 2, carbonization reaction: Carbon dioxide gas is introduced into the lithium ammonia water obtained in Step 1 to carry out the reaction, and the pH value of the reaction system is controlled by adjusting the amount of ammonia and carbon dioxide introduced. The reaction continues until the system temperature naturally rises to a stable state and no longer rises. The principle behind the above steps is that the crystal precipitation and conversion process achieves the separation and fixation of lithium. By dynamically adjusting the ratio of ammonia gas to carbon dioxide to maintain alkalinity, the pH of the reaction system can be precisely controlled. Carbon dioxide is introduced into the alkaline lithium ammonia solution, where it first reacts with H2O to generate bicarbonate ions. Lithium ions in the solution combine with bicarbonate ions to form lithium bicarbonate, which has extremely low solubility. The exothermic reaction causes the system temperature to rise naturally and tend to stabilize. The high-temperature environment above 90°C is particularly conducive to the rapid decomposition of the intermediate product lithium bicarbonate into lithium carbonate, thereby increasing the reaction rate and conversion rate.

[0014] Step 3, solid-liquid separation: The reaction mixture obtained in step 2 is filtered under heat preservation conditions, and the resulting filter cake is washed with deionized water until the pH value of the filtrate is 10.5 to 11.5; The principle behind the above steps is to use high-temperature deionized water for washing, mainly based on two principles: First, the viscosity of water decreases and its permeability increases at high temperatures, which is beneficial for thoroughly washing away impurity ions (such as Na⁺, Cl⁻, NH⁴⁺, etc.) adsorbed on the surface and in the gaps of particles; second, the solubility of lithium carbonate in hot water is less than that in cold water, but the solubility of impurity salts (such as sodium chloride and ammonium chloride) is usually higher. By controlling the pH value at the end of the washing process to 10.5-11.5, which is close to the pH of a saturated lithium carbonate solution, impurities can be effectively washed away while minimizing the dissolution loss of lithium carbonate in the product during the washing process.

[0015] Step 4, Drying: The washed filter cake is dried at high temperature and crushed to obtain lithium carbonate product.

[0016] The principle behind the above steps is that high-temperature treatment evaporates the moisture physically adsorbed on the surface and in the internal capillary channels of lithium carbonate particles. Appropriate drying temperature and time ensure that the moisture is fully removed while avoiding excessive temperature that could cause the lithium carbonate to decompose. The crushing process after drying adjusts the particle size of the product to meet the physical specifications required for different applications.

[0017] Furthermore, in step 1, the lithium qualified solution has a Li⁺ concentration of 14–40 g / L.

[0018] Furthermore, in step 1, the qualified lithium solution may contain Na⁺, with a concentration ≤50g / L.

[0019] Further, in step 1, the permissible impurity ions in the qualified lithium solution include: B element concentration ≤ 3 g / L, Mg... 2 ⁺ and Ca 2 The concentration of ⁺ is ≤30g / L.

[0020] Furthermore, in step 1, the temperature of the qualified lithium solution at a certain temperature is 25-85°C.

[0021] Furthermore, in step 2, the pH value of the reaction system is controlled between 10 and 14.

[0022] Furthermore, in step 3, the temperature of the deionized water used for washing is 80–95°C.

[0023] Furthermore, in step 4, the temperature range of the high-temperature drying is 150–480°C, and the drying time is more than 5 hours.

[0024] This invention also protects the application of the above method for the production of industrial-grade lithium carbonate products with a purity ≥ 95% and battery-grade lithium carbonate products with a purity ≥ 99.6%.

[0025] Compared with existing technologies, the present invention has the following beneficial effects: 1. By completely replacing industrial sodium carbonate with ammonia and carbon dioxide as reactants, the introduction of exogenous impurities (such as Ca, Mg, and B) is fundamentally eliminated. Simultaneously, through dynamic pH control and high-temperature deionized water washing, the co-precipitation and surface adsorption of impurity ions such as sodium are effectively suppressed, ensuring that the purity of the resulting lithium carbonate product consistently reaches a high standard of no less than 99.9% (Li₂CO₃-O₃ grade). This meets the stringent requirements of high-end lithium-ion batteries for key raw materials and significantly enhances the product's added value.

[0026] 2. This invention utilizes the exothermic dissolution of ammonia gas to spontaneously heat the reaction system and stabilize it at a suitable temperature above 90°C. This condition not only promotes the rapid decomposition of the intermediate product lithium bicarbonate and improves reaction kinetic efficiency, but also eliminates the need for significant dilution of the feed solution to suppress co-precipitation during production. This significantly increases the single-precipitation conversion rate of lithium to 91-96%, which is significantly better than the approximately 85% level of traditional processes. The entire process uses carbon dioxide as the carbon source, operates under mild conditions, requires no high-pressure equipment, and simplifies subsequent separation and wastewater treatment processes, combining the advantages of being green, low-carbon, and highly feasible for industrialization.

[0027] 3. The method of this invention provides an efficient and reliable technical route for the direct preparation of high-purity lithium carbonate from my country's abundant salt lake lithium resources. This will help promote the upgrading of the domestic salt lake lithium extraction product structure towards high-end products, reduce dependence on imported high-purity lithium salts, and has positive significance for enhancing the self-control and international competitiveness of my country's new energy industry chain. Attached Figure Description

[0028] Figure 1 This is a process flow diagram of the method of the present invention; Figure 2 XRD pattern of Li2CO3-7# sample powder prepared for this invention. Detailed Implementation

[0029] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Process principle: After preparing a qualified lithium solution from brine using a membrane separation-adsorption coupling method, ammonia gas is introduced into the solution until saturation is achieved under incubation conditions (room temperature to 85°C), forming ammonia-lithium water. Subsequently, carbon dioxide gas is introduced into the system. As the reaction proceeds, the solution gradually becomes turbid, indicating the precipitation of lithium carbonate. By alternating or continuously adjusting the amount of ammonia and carbon dioxide introduced, the pH of the reaction system is maintained within the range of 10–14, and the reaction temperature is allowed to naturally rise to a stable state (i.e., no longer rising), achieving efficient lithium carbonate production. After the reaction is complete, solid-liquid separation is performed under incubation conditions. The resulting solid precipitate is washed with deionized water at 80–95°C until the pH of the filtrate is in the range of 10.5–11.5, and then dried and crushed at high temperature to finally obtain a high-purity brine lithium carbonate product.

[0031] Example 1 A method for preparing high-purity lithium carbonate from brine The qualified lithium solution has a lithium concentration of 14 g / L, a Na⁺ content of 50 g / L, a boron concentration of 3 g / L, and a magnesium content of 14 g / L. 2 ⁺ and Ca 2 The raw materials were all at a concentration of 30 g / L. 5L of qualified lithium solution was placed in an insulated container and heated to 25℃. Under the insulated condition, ammonia gas was introduced into the qualified lithium solution until saturation, resulting in ammonia-lithium water. At this point, the solution temperature reached 58℃. Carbon dioxide gas was then introduced into the ammonia-lithium water to continue the reaction. As the reaction proceeded, the solution gradually became turbid. Ammonia and carbon dioxide were introduced simultaneously, and the pH value of the reaction system was controlled to 14 by adjusting the amount of ammonia and carbon dioxide introduced. The reaction continued until the system temperature naturally rose to a stable state and no longer increased. At this point, the solution temperature reached its highest value of 72℃ and was maintained for 5 minutes. The solution was filtered while hot, and the filter cake was repeatedly washed with 95℃ deionized water until the pH reached 11.5. The washed filter cake was then dried at 150℃ for more than 5 hours and then crushed to obtain lithium carbonate product Li2CO3-1#. The Li concentration in the filtrate was measured to be 1.82g / L. Using the formula Li conversion rate = (lithium concentration in the original solution - lithium concentration in the filtrate) / lithium concentration in the original solution × 100%, the lithium conversion rate was calculated to be 87%.

[0032] Example 2 A method for preparing high-purity lithium carbonate from brine The qualified lithium solution has a lithium concentration of 14 g / L, a Na⁺ content of 50 g / L, a boron concentration of 3 g / L, and a magnesium content of 14 g / L. 2 ⁺ and Ca 2 The raw materials were all at a concentration of 30 g / L. 5L of qualified lithium solution was placed in an insulated container and heated to 65℃. Under the insulated condition, ammonia gas was introduced into the qualified lithium solution until saturation, resulting in ammonia-lithium water. At this point, the solution temperature reached 95℃. Carbon dioxide gas was then introduced into the ammonia-lithium water to continue the reaction. As the reaction proceeded, the solution gradually became turbid. Ammonia and carbon dioxide were introduced simultaneously, and the pH value of the reaction system was controlled to 12 by adjusting the amount of ammonia and carbon dioxide introduced. The reaction continued until the system temperature naturally rose to a stable state and no longer increased. At this point, the solution temperature reached its maximum value of 95℃ and was maintained for 5 minutes. The solution was then filtered while hot, and the filter cake was repeatedly washed with 95℃ deionized water until the pH reached 11.5. The washed filter cake was then dried at 180℃ for more than 5 hours and then crushed to obtain lithium carbonate product Li2CO3-2#. The Li concentration in the filtrate was measured to be 1.26 g / L. Using the formula Li conversion rate = (lithium concentration in the original solution - lithium concentration in the filtrate) / lithium concentration in the original solution × 100%, the lithium conversion rate was calculated to be 91%.

[0033] Example 3 A method for preparing high-purity lithium carbonate from brine The qualified lithium solution has a lithium concentration of 14 g / L, a Na⁺ content of 50 g / L, a boron concentration of 3 g / L, and a magnesium content of 14 g / L. 2 ⁺ and Ca 2 The raw materials were all at a concentration of 30 g / L. Take 5L of qualified lithium solution and place it in an insulated container. Heat it to 85℃. Under the insulated condition, ammonia gas is introduced into the qualified lithium solution until saturation, resulting in ammonia-lithium water. At this point, the solution temperature reaches 95℃. Continue to introduce carbon dioxide gas into the ammonia-lithium water to carry out the reaction. As the reaction proceeds, the solution gradually becomes turbid. Simultaneously, ammonia and carbon dioxide are introduced. By adjusting the amount of ammonia and carbon dioxide introduced, the pH value of the reaction system is controlled to 12. The reaction continues until the system temperature naturally rises to a stable state and no longer rises. At this point, the solution temperature reaches its maximum value of 95℃ and is maintained for 5 minutes. Filter while hot, and repeatedly wash the filter cake with 95℃ deionized water until the pH reaches 11.5. The washed filter cake is dried at 300℃ for more than 5 hours and then crushed to obtain lithium carbonate product Li2CO3-3#. The Li concentration in the filtrate is detected to be 1.26g / L. Using the formula Li conversion rate = (lithium concentration in original solution - lithium concentration in filtrate) / lithium concentration in original solution × 100%, the lithium conversion rate is calculated to be 91%.

[0034] Example 4 A method for preparing high-purity lithium carbonate from brine The qualified lithium solution has a lithium concentration of 22 g / L, a Na⁺ content of 20 g / L, a boron concentration of 1.2 g / L, and a magnesium content of [missing information]. 2 ⁺ and Ca 2 The raw materials were all ⁺ with a concentration of 15 g / L. 5L of qualified lithium solution was placed in an insulated container and heated to 35℃. Under the insulated condition, ammonia gas was introduced into the qualified lithium solution until saturation, resulting in ammonia-lithium water. At this point, the solution temperature reached 85℃. Carbon dioxide gas was then introduced into the ammonia-lithium water to continue the reaction. As the reaction proceeded, the solution gradually became turbid. Ammonia and carbon dioxide were introduced simultaneously, and the pH value of the reaction system was controlled to 13 by adjusting the amount of ammonia and carbon dioxide introduced. The reaction continued until the system temperature naturally rose to a stable state and no longer increased. At this point, the solution temperature reached its maximum value of 95℃ and was maintained for 5 minutes. The solution was filtered while hot, and the filter cake was repeatedly washed with 95℃ deionized water until the pH reached 11.5. The washed filter cake was then dried at 480℃ for more than 5 hours and then crushed to obtain lithium carbonate product Li2CO3-4#. The Li concentration in the filtrate was measured to be 1.54 g / L. Using the formula Li conversion rate = (lithium concentration in the original solution - lithium concentration in the filtrate) / lithium concentration in the original solution × 100%, the lithium conversion rate was calculated to be 93%.

[0035] Example 5 A method for preparing high-purity lithium carbonate from brine The qualified lithium solution has a lithium concentration of 29 g / L, a Na⁺ content of 9 g / L, a boron concentration of 0.6 g / L, and a magnesium content of [missing information]. 2 ⁺ and Ca 2 The raw materials were all 5g / L in concentration. 5L of qualified lithium solution was placed in an insulated container and heated to 45℃. Under the insulated condition, ammonia gas was introduced into the qualified lithium solution until saturation, resulting in ammonia-lithium water. At this point, the solution temperature reached 95℃. Carbon dioxide gas was then introduced into the ammonia-lithium water to continue the reaction. As the reaction proceeded, the solution gradually became turbid. Ammonia and carbon dioxide were introduced simultaneously, and the pH value of the reaction system was controlled to 13 by adjusting the amount of ammonia and carbon dioxide introduced. The reaction continued until the system temperature naturally rose to a stable state and no longer increased. At this point, the solution temperature reached its maximum value of 95℃ and was maintained for 5 minutes. The solution was filtered while hot, and the filter cake was repeatedly washed with 95℃ deionized water until the pH reached 11. The washed filter cake was dried at 320℃ for more than 5 hours and then crushed to obtain lithium carbonate product Li2CO3-5#. The Li concentration in the filtrate was measured to be 1.74 g / L. Using the formula Li conversion rate = (lithium concentration in original solution - lithium concentration in filtrate) / lithium concentration in original solution × 100%, the lithium conversion rate was calculated to be 94%.

[0036] Example 6 A method for preparing high-purity lithium carbonate from brine The qualified lithium solution has a lithium concentration of 40 g / L, a Na⁺ content of 7 g / L, a boron concentration of 0.3 g / L, and a magnesium content of [missing information]. 2 ⁺ and Ca 2 The raw materials all had a concentration of 3 g / L. 5L of qualified lithium solution was placed in an insulated container and heated to 35℃. Under the insulated condition, ammonia gas was introduced into the qualified lithium solution until saturation, resulting in ammonia-lithium water. At this point, the solution temperature reached 87℃. Carbon dioxide gas was then introduced into the ammonia-lithium water to continue the reaction. As the reaction proceeded, the solution gradually became turbid. Ammonia and carbon dioxide were introduced simultaneously, and the pH value of the reaction system was controlled to 14 by adjusting the amount of ammonia and carbon dioxide introduced. The reaction continued until the system temperature naturally rose to a stable state and no longer increased. At this point, the solution temperature reached its maximum value of 95℃ and was maintained for 5 minutes. The solution was filtered while hot, and the filter cake was repeatedly washed with 95℃ deionized water until the pH reached 11. The washed filter cake was dried at 200℃ for more than 5 hours and then crushed to obtain lithium carbonate product Li2CO3-6#. The Li concentration in the filtrate was measured to be 1.60 g / L. Using the formula Li conversion rate = (lithium concentration in the original solution - lithium concentration in the filtrate) / lithium concentration in the original solution × 100%, the lithium conversion rate was calculated to be 96%.

[0037] Example 7 A method for preparing high-purity lithium carbonate from brine The qualified lithium solution has a lithium concentration of 32 g / L, a Na⁺ content of 7 g / L, a boron concentration of 0.3 g / L, and a magnesium content of [missing information]. 2 ⁺ and Ca 2 The raw materials all had a concentration of 3 g / L. 5L of qualified lithium solution was placed in an insulated container and heated to 35℃. Under the insulated condition, ammonia gas was introduced into the qualified lithium solution until saturation, resulting in ammonia-lithium water. At this point, the solution temperature reached 86℃. Carbon dioxide gas was then introduced into the ammonia-lithium water to continue the reaction. As the reaction proceeded, the solution gradually became turbid. Ammonia and carbon dioxide were introduced simultaneously, and the pH value of the reaction system was controlled to 14 by adjusting the amount of ammonia and carbon dioxide introduced. The reaction continued until the system temperature naturally rose to a stable state and no longer increased. At this point, the solution temperature reached its maximum value of 95℃ and was maintained for 5 minutes. The solution was filtered while hot, and the filter cake was repeatedly washed with 85℃ deionized water until the pH reached 10.5. The washed filter cake was then dried at 150℃ for more than 5 hours and then crushed to obtain the lithium carbonate product Li2CO3-7#. The Li concentration in the filtrate was measured to be 1.60 g / L. Using the formula Li conversion rate = (lithium concentration in the original solution - lithium concentration in the filtrate) / lithium concentration in the original solution × 100%, the lithium conversion rate was calculated to be 95%.

[0038] Example 8 A method for preparing high-purity lithium carbonate from brine The qualified lithium solution has a lithium concentration of 40 g / L, a Na⁺ content of 15 g / L, a boron concentration of 1.2 g / L, and a magnesium content of [missing information]. 2 ⁺ and Ca 2 The raw materials were all ⁺ with a concentration of 15 g / L. 5L of qualified lithium solution was placed in an insulated container and heated to 35℃. Under the insulated condition, ammonia gas was introduced into the qualified lithium solution until saturation, resulting in ammonia-lithium water. At this point, the solution temperature reached 87℃. Carbon dioxide gas was then introduced into the ammonia-lithium water to continue the reaction. As the reaction proceeded, the solution gradually became turbid. Ammonia and carbon dioxide were introduced simultaneously, and the pH value of the reaction system was controlled to 14 by adjusting the amount of ammonia and carbon dioxide introduced. The reaction continued until the system temperature naturally rose to a stable state and no longer increased. At this point, the solution temperature reached its maximum value of 95℃ and was maintained for 5 minutes. The solution was then filtered while hot, and the filter cake was repeatedly washed with 80℃ deionized water until the pH reached 11. The washed filter cake was then dried at 220℃ for more than 5 hours and then crushed to obtain the lithium carbonate product Li2CO3-8#. The Li concentration in the filtrate was measured to be 2.4 g / L. Using the formula Li conversion rate = (lithium concentration in the original solution - lithium concentration in the filtrate) / lithium concentration in the original solution × 100%, the lithium conversion rate was calculated to be 94%.

[0039] Example 9 The lithium carbonate prepared in the above 8 examples was tested for its main components and impurity elements in brine lithium carbonate according to GBT 23853-2022. The results are shown in Table 1 below.

[0040] Table 1. Results of lithium carbonate sample composition determination Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing high-purity lithium carbonate from brine, characterized in that, Specifically, the steps include the following: Step 1, Preparation of ammonia-lithium water: Under heat preservation conditions, ammonia gas is introduced into a qualified lithium solution at a certain temperature until saturation is achieved to obtain ammonia-lithium water; Step 2, carbonization reaction: Carbon dioxide gas is introduced into the lithium ammonia water obtained in Step 1 to carry out the reaction, and the pH value of the reaction system is controlled by adjusting the amount of ammonia and carbon dioxide introduced. The reaction continues until the system temperature naturally rises to a stable state and no longer rises. Step 3, solid-liquid separation and washing: The reaction mixture obtained in step 2 is filtered under heat preservation conditions, and the resulting filter cake is washed with deionized water until the pH value of the filtrate is 10.5 to 11.5; Step 4, Drying: The washed filter cake is dried at high temperature and crushed to obtain lithium carbonate product.

2. The method for preparing high-purity lithium carbonate from brine according to claim 1, characterized in that, In step 1, the lithium qualified solution has a Li⁺ concentration of 14–40 g / L.

3. The method for preparing high-purity lithium carbonate from brine according to claim 1, characterized in that, In step 1, the qualified lithium solution may contain Na⁺, with a concentration ≤50g / L.

4. The method for preparing high-purity lithium carbonate brine according to claim 1, characterized in that, In step 1, the permissible impurity ions in the qualified lithium solution include: B element concentration ≤ 3 g / L, Mg 2 ⁺ and Ca 2 The concentration of ⁺ is ≤30g / L.

5. The method for preparing high-purity lithium carbonate from brine according to claim 1, characterized in that, In step 1, the temperature of the qualified lithium solution at a certain temperature is 25-85℃.

6. The method for preparing high-purity lithium carbonate brine according to claim 1, characterized in that, In step 2, the pH value of the reaction system is controlled between 10 and 14.

7. The method for preparing high-purity lithium carbonate brine according to claim 1, characterized in that, In step 3, the temperature of the deionized water used for washing is 80–95°C.

8. The method for preparing high-purity lithium carbonate brine according to claim 1, characterized in that, In step 4, the temperature range for high-temperature drying is 150–480°C, and the drying time is more than 5 hours.

9. The application of the method for preparing high-purity lithium carbonate brine according to any one of claims 1-8, characterized in that, The method is used for the production of industrial-grade lithium carbonate products with a purity of ≥95% and battery-grade lithium carbonate products with a purity of ≥99.6%.

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