A method for producing battery-grade lithium carbonate by gas-liquid circulation

Abstract

The application provides a method for producing battery-grade lithium carbonate by gas-liquid circulation, which comprises the following steps: preparing a slurry by mixing industrial-grade lithium carbonate, water and quicklime, and performing causticization reaction on the slurry; performing purification and carbonization on the obtained lithium hydroxide solution to obtain battery-grade lithium carbonate and a post-carbonization solution; recovering part of the lithium carbonate by one-time evaporation concentration and crystallization on the post-carbonization solution, and adjusting the pH value of the obtained one-time concentrated solution by adding acid to convert lithium salts in the one-time concentrated solution into soluble lithium salts; performing secondary evaporation concentration and crystallization on the one-time concentrated solution, discharging most of the sodium and potassium salts in the system, and obtaining a secondary concentrated solution; further recovering lithium carbonate by performing lithium precipitation on the secondary concentrated solution by using sodium carbonate; discharging sodium and potassium salts by crystallization on the obtained lithium precipitation solution; and obtaining a post-crystallization solution which can be recycled. The production method has the advantages of low cost, less use of reagents, good quality of the obtained lithium carbonate product, high recovery rate, realization of the recycling of carbon dioxide and liquid in the whole process, environmental friendliness, short process, and considerable industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of battery-grade lithium carbonate production technology, specifically relating to a method for producing battery-grade lithium carbonate through gas-liquid recycling. Background Technology

[0002] Lithium and its related industries are emerging forces in the 21st-century energy industry. Lithium possesses unique properties such as high electrical conductivity and high electrochemical activity, earning it the titles of "energy metal" and "important element driving the world forward." Lithium carbonate is a fundamental industrial product of lithium and has been widely used in lithium-ion batteries, pharmaceuticals, and aerospace applications. It is a raw material for preparing other lithium salts and an essential raw material for new energy battery materials such as lithium iron phosphate and lithium hexafluorophosphate. With the rapid development of new energy vehicles, the demand for battery-grade lithium carbonate has surged.

[0003] Battery-grade lithium carbonate has strict requirements for product purity and impurities, and is usually prepared from industrial-grade lithium carbonate. Currently, industrial methods for producing battery-grade lithium carbonate from industrial-grade lithium carbonate include hydrogenation pyrolysis, bipolar film carbonation, and causticization carbonation. Among these, the lithium bicarbonate pyrolysis method produces battery-grade lithium carbonate with poor particle size control and inconsistent particle size. Chinese patent document CN115286017A discloses a method for preparing battery-grade lithium carbonate, which utilizes the carbonation and hydrogenation reaction of carbon dioxide and crude lithium carbonate solution to obtain a lithium bicarbonate solution, and then heats the lithium bicarbonate solution to obtain battery-grade lithium carbonate. However, this technology suffers from difficult-to-control pyrolysis processes, significant lithium loss, and a tendency for the prepared battery-grade lithium carbonate to agglomerate, thus lacking cost advantages. Chinese patent document CN107298450B discloses a method for preparing lithium hydroxide and lithium carbonate using a soluble lithium salt solution. This method utilizes a bipolar membrane electrodialysis device to electrolyze the soluble lithium salt solution, obtaining a lithium hydroxide solution at the cathode. High-purity lithium carbonate is then obtained through carbonization. However, this method still suffers from a complex electrodialysis system, expensive membrane materials, and the need to first convert industrial-grade lithium carbonate into soluble lithium salts, hindering large-scale application. Chinese patent document CN115340109A discloses a method for preparing high-purity lithium carbonate using crude lithium carbonate. This method utilizes the causticization reaction of calcium hydroxide and crude lithium carbonate to obtain a lithium hydroxide solution, which is then carbonized to obtain high-purity lithium carbonate. However, this method does not consider the treatment of calcium slag and the mother liquor after carbonization, resulting in lithium loss. The untreated carbonization mother liquor enters the recycling process, easily leading to the accumulation of impurity ions and ultimately affecting product quality.

[0004] Lithium precipitate mother liquor typically contains a high concentration of lithium ions and has recycling value. Existing lithium precipitate mother liquor treatment technologies mainly include freeze crystallization, evaporation concentration, extraction, and adsorption. Extraction and adsorption methods utilize lithium extractants and lithium ion sieves to selectively extract lithium from lithium precipitate mother liquor, offering high lithium selectivity. However, the recovery and reuse of extractants and ion sieves are difficult and costly, hindering industrial development. Freeze crystallization and evaporation concentration are early recycling technologies for sodium carbonate lithium precipitate mother liquor, and their application is relatively mature. However, freeze crystallization has relatively high technical barriers, and the reaction rate is slower than high-temperature evaporation crystallization, making it difficult to control product particle size and morphology. Chinese patent document CN106882822A discloses a method for recovering lithium from lithium precipitate mother liquor to battery-grade lithium carbonate. This method involves freeze-curing the lithium precipitate mother liquor from the reaction of sodium carbonate and lithium sulfate to precipitate sodium sulfate. CN110451536A discloses a method for recovering lithium from battery-grade lithium carbonate mother liquor, using a synergistic process of freeze crystallization and evaporation concentration to prepare sodium sulfate and battery-grade lithium carbonate, but the lithium yield is low. Chinese patent document CN104925837A discloses a method for preparing lithium salts by recovering lithium carbonate precipitation mother liquor from battery-grade lithium carbonate. This method utilizes lithium phosphate precipitation, which improves the lithium yield, but it faces environmental and cost pressures related to the treatment of phosphorus-containing wastewater.

[0005] The causticization carbonation method is a low-consumption and high-efficiency method for producing battery-grade lithium carbonate from crude lithium carbonate. However, there is currently a lack of process technology for recycling this lithium precipitation mother liquor system, and the problem of impurity enrichment such as sodium and potassium remains unresolved, still posing environmental problems related to wastewater and waste gas emissions. Therefore, developing a new low-cost, wastewater- and waste gas-free process for producing battery-grade lithium carbonate is of great practical significance. Summary of the Invention

[0006] To address the above problems, this invention provides a method for producing battery-grade lithium carbonate that enables gas-liquid recycling.

[0007] To achieve the above objectives, the present invention proposes the following solution:

[0008] This invention provides a method for producing battery-grade lithium carbonate through gas-liquid circulation, particularly addressing the gas-liquid-solid three-phase characteristics of each step in the causticization and carbonization route for preparing battery-grade lithium carbonate from industrial-grade lithium carbonate. To address the problem of impurity enrichment such as sodium and potassium in this solution system, the solution circulation route is designed based on the theoretical guidance of the thermodynamic behavior characteristics of salt solutions.

[0009] Specifically, the present invention provides a method for producing battery-grade lithium carbonate through gas-liquid recycling, comprising:

[0010] (1) Prepare a slurry with industrial grade lithium carbonate, water and quicklime and carry out a causticization reaction. After solid-liquid separation, obtain lithium hydroxide solution and causticization residue.

[0011] (2) After evaporating and concentrating the lithium hydroxide solution, cool and crystallize it. Then, redissolve and finely filter the resulting crystals to obtain a refined lithium hydroxide solution.

[0012] (3) Carbon dioxide is introduced into the lithium hydroxide refining solution to carry out a carbonization reaction. After carbonization, solid-liquid separation is carried out to obtain battery-grade lithium carbonate and carbonized liquid.

[0013] (4) The carbonized liquid is subjected to first evaporation concentration and cooling crystallization, and filtered to obtain lithium carbonate and primary concentrate. Acid is added to the primary concentrate to adjust the pH value, and then second evaporation concentration and cooling crystallization are performed. Sodium potassium salt and secondary concentrate are obtained by solid-liquid separation. Sodium carbonate is added to the secondary concentrate to precipitate lithium to obtain lithium carbonate and lithium precipitated liquid. The lithium precipitated liquid is then subjected to crystallization and solid-liquid separation to obtain sodium potassium salt and crystallized liquid.

[0014] Preferably, in step (1), the Li2CO3 content in the industrial lithium carbonate is ≥98.5 wt.%, and the CaO content in the quicklime is ≥90 wt.%.

[0015] The Li content of the obtained lithium hydroxide solution is 8.5–9.5 g / L.

[0016] Preferably, in step (1), the molar ratio of Li2CO3 to CaO in the slurry is 1:1.05 to 1.5, and the solid-liquid ratio is 1:8 to 12.

[0017] The causticizing reaction is carried out at a temperature of 80–95°C; preferably, the causticizing reaction is accelerated by stirring during the causticizing reaction, with a stirring rate of 200–400 rpm; the causticizing reaction is carried out for a time of 1–10 h.

[0018] Preferably, in step (2), the temperature of the steam for evaporation and concentration is 100-120°C, and the temperature for cooling and crystallization is 40-50°C.

[0019] Preferably, in step (2), the Li content of the lithium hydroxide solution is 25-35 g / L; and the Li content of the resulting refined lithium hydroxide solution is 25-35 g / L.

[0020] Preferably, in step (3), the carbon dioxide is industrial-grade carbon dioxide; the temperature of the carbonization reaction is 20-80°C; the final pH value of the carbonization reaction is 9.5-10.5; by optimizing the carbonization conditions, on the one hand, the carbonization of lithium hydroxide can be maximized, and on the other hand, a large amount of carbon dioxide and lithium carbonate can be avoided from reacting to form lithium bicarbonate.

[0021] Preferably, the Li content of the resulting carbonized liquid is 2–6 g / L.

[0022] Preferably, in step (4), the temperature of the first evaporation and concentration is 100-120°C, the first evaporation and concentration ratio is 2-5:1, and the temperature of the cooling and crystallization is 20-40°C.

[0023] The second evaporation and concentration temperature is 100–120°C, the second evaporation and concentration ratio is 2–5:1, and the cooling and crystallization temperature is 20–40°C. More preferably, an MVR multi-effect evaporator is used for both evaporations to improve the solution evaporation and concentration efficiency.

[0024] Preferably, in step (4), the pH value adjusted by adding acid is 5-7; the acid is sulfuric acid or hydrochloric acid; the carbon dioxide generated by adjusting the pH value is collected, concentrated, and returned to step (3) for carbonation reaction. Since both lithium carbonate and sodium / potassium salts are saturated in the solution after the first concentration, the lithium form is transformed by adding acid, and the sodium / potassium salts are separated from lithium by subsequent secondary evaporation and concentration. Optionally, sulfuric acid with a concentration of 50-98% can be used, and hydrochloric acid with a concentration of 10-36% can be used.

[0025] Preferably, in step (4), the amount of sodium carbonate added is 1.05 to 1.1 times the theoretical amount required to achieve complete lithium precipitation in the secondary concentrate. After secondary evaporation and concentration, lithium is enriched in the solution. Using sodium carbonate for lithium precipitation at this point significantly reduces the consumption of sodium carbonate and the precipitation efficiency.

[0026] Since the lithium carbonate obtained by one-time evaporation concentration precipitation and sodium carbonate precipitation is of high quality, it can be used as a causticizing raw material with industrial-grade lithium carbonate. Preferably, in step (4), the lithium carbonate obtained by cooling crystallization and sodium carbonate precipitation is returned to step (1) to replace at least part of the industrial lithium carbonate.

[0027] Preferably, in step (4), the crystallized liquid is returned to step (1) to prepare slurry or combined with the carbonized liquid for processing, so as to achieve complete lithium recovery and lithium closed loop.

[0028] Preferably, in step (1), the causticized slag is calcined at high temperature to obtain recycled quicklime and carbon dioxide;

[0029] Further preferred, the carbon dioxide concentration is used for the carbonization reaction in step (3), which can be achieved by collecting, compressing and storing the carbon dioxide, and using it in parallel with industrial-grade carbon dioxide for the carbonization in step (3); when the CaO content in the recycled quicklime is ≥90wt.%, it is returned to step (1) as raw material, and when the CaO content in the recycled quicklime is <90wt.%, it is sold externally as building filler.

[0030] Preferably, before high-temperature calcination, the causticized slag is washed with water to obtain washing slag and washing water. The washing slag is used for high-temperature calcination to regenerate quicklime, and the washing water is returned to step (1) to prepare slurry. On the one hand, lithium recovery can be achieved, and on the other hand, washing water can be recycled.

[0031] Preferably, in step (4), the lithium content in the lithium carbonate obtained by cooling crystallization and sodium carbonate precipitation is 17-18.7 wt.%; and the lithium content of the sodium potassium salt in both steps of step (4) is less than 0.3 wt.%.

[0032] Throughout the entire process, the calcination of the caustic slag and the pH adjustment and carbon removal processes both generate a considerable amount of carbon dioxide, which can be fully collected and used in the carbonization step to achieve carbon dioxide gas recycling.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. This invention utilizes industrial-grade lithium carbonate as raw material to prepare battery-grade lithium carbonate, resulting in high-quality products with good consistency. The purity of the prepared lithium carbonate product is consistently above 99.5%, and the particle size D50 is consistently between 4 and 6 μm. With the advantage of a short process flow, the magnetic foreign matter content of the product is consistently below 120 ppb, giving it market competitiveness.

[0035] 2. Based on the characteristics of the gas-liquid-solid three-phase system in each process, this invention addresses the problem of sodium and potassium impurity accumulation in the solution system. Guided by the thermodynamic behavior of salt solutions, a solution circulation route is designed. Carbonization is achieved through carbon dioxide, and the carbonized liquid is treated by evaporation concentration and simple modulation to achieve lithium closed-loop processing, significantly improving the utilization rate of raw materials. The overall lithium yield reaches over 99%, and the accumulated sodium and potassium are discharged from the system during circulation, avoiding the accumulation of sodium and potassium impurities, ensuring product purity, and the produced sodium and potassium salts can be sold as by-products.

[0036] 3. This invention does not involve the use of chemical products that are highly harmful to equipment and the environment, especially avoiding the use of nitrates, fluorides, and phosphides. It has low requirements for equipment corrosion resistance and is environmentally friendly. Furthermore, through innovative process design, this invention not only reduces the amount of acid required throughout the process, achieving the use of light reagents, but also reduces energy consumption, thus effectively reducing costs, equipment corrosion, and environmental pressure, making it suitable for large-scale industrial applications. This invention fully utilizes the causticizing slag to regenerate quicklime, using the carbon dioxide generated in the process for carbonization. The liquid generated in the process, since it does not introduce harmful impurities, can be used for slurry preparation, thereby achieving gas-liquid phase recycling in the process flow, greatly reducing the environmental and cost pressures of wastewater and waste gas treatment. In summary, this invention has advantages such as short process, simple operation, high controllability, low cost, and green environmental protection, and has considerable prospects for industrial application. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a process flow diagram of the present invention.

[0039] Figure 2 The image shows the XRD pattern of lithium carbonate obtained from the first evaporation and concentration in Example 3. Detailed Implementation

[0040] This invention provides a method for producing battery-grade lithium carbonate via a gas-liquid cycle, comprising:

[0041] (1) Prepare a slurry with industrial grade lithium carbonate, water and quicklime and carry out a causticization reaction. After solid-liquid separation, obtain lithium hydroxide solution and causticization residue.

[0042] (2) After evaporating and concentrating the lithium hydroxide solution, cool and crystallize it. Then, redissolve and finely filter the resulting crystals to obtain a refined lithium hydroxide solution.

[0043] (3) Carbon dioxide is introduced into the lithium hydroxide refining solution to carry out a carbonization reaction. After carbonization, solid-liquid separation is carried out to obtain battery-grade lithium carbonate and carbonized liquid.

[0044] (4) The carbonized liquid is subjected to first evaporation concentration and cooling crystallization, and filtered to obtain lithium carbonate and primary concentrate. Acid is added to the primary concentrate to adjust the pH value, and then second evaporation concentration and cooling crystallization are performed. Sodium potassium salt and secondary concentrate are obtained by solid-liquid separation. Sodium carbonate is added to the secondary concentrate to precipitate lithium to obtain lithium carbonate and lithium precipitated liquid. The lithium precipitated liquid is then subjected to crystallization and solid-liquid separation to obtain sodium potassium salt and crystallized liquid.

[0045] As a preferred embodiment, in step (1), the Li2CO3 content in the industrial lithium carbonate is ≥98.5wt.%, and the CaO content in the quicklime is ≥90wt.%.

[0046] As a preferred embodiment, in step (1), the Li content of the obtained lithium hydroxide solution is 8.5 to 9.5 g / L.

[0047] As a preferred embodiment, in step (1), the molar ratio of Li2CO3 to CaO in the slurry is 1:1.05 to 1.5, and the solid-liquid ratio is 1:8 to 12.

[0048] As a preferred embodiment, in step (1), the temperature of the causticizing reaction is 80-95°C; preferably, the causticizing reaction is accelerated by stirring during the causticizing reaction, and the stirring rate is 200-400 rpm; the time of the causticizing reaction is 1-10 h.

[0049] As a preferred embodiment, in step (2), the temperature of the steam for evaporation and concentration is 100-120°C, and the temperature for cooling and crystallization is 40-50°C.

[0050] As a preferred embodiment, the Li content of the lithium hydroxide solution is 25-35 g / L; the Li content of the resulting refined lithium hydroxide solution is 25-35 g / L.

[0051] As a preferred embodiment, in step (2), the micropores of the precision filter are 0.2 to 1 micrometer.

[0052] As a preferred embodiment, in step (3), the carbon dioxide is industrial-grade carbon dioxide; the temperature of the carbonization reaction is 20-80°C; the final pH value of the carbonization reaction is 9.5-10.5; by optimizing the carbonization conditions, on the one hand, the carbonization of lithium hydroxide can be maximized, and on the other hand, a large amount of carbon dioxide and lithium carbonate can be avoided from reacting to form lithium bicarbonate.

[0053] As a preferred embodiment, the Li content of the resulting carbonized liquid is 2-6 g / L.

[0054] As a preferred embodiment, in step (4), the temperature of the first evaporation and concentration is 100-120°C, the first evaporation and concentration ratio is 2-5:1, and the temperature of the cooling and crystallization is 20-40°C.

[0055] As a preferred embodiment, the temperature of the second evaporation and concentration is 100–120°C, the second evaporation and concentration ratio is 2–5:1, and the temperature of the cooling and crystallization is 20–40°C. More preferably, an MVR multi-effect evaporator is used for both evaporations to improve the solution evaporation and concentration efficiency.

[0056] As a preferred embodiment, in step (4), the pH value adjusted by adding acid is 5-7; the acid is sulfuric acid or hydrochloric acid. Since both lithium carbonate and sodium / potassium salts are saturated in the solution after the first concentration, the lithium form is converted by adding acid, and the sodium / potassium salts are separated from lithium by subsequent secondary evaporation and concentration. Optionally, sulfuric acid with a concentration of 50-98% can be used, and hydrochloric acid with a concentration of 10-36% can be used.

[0057] As a preferred embodiment, in step (4), the amount of sodium carbonate added is 1.05 to 1.1 times the theoretical amount required to achieve complete lithium precipitation in the secondary concentrate. After secondary evaporation and concentration, lithium is enriched in the solution. Using sodium carbonate for lithium precipitation at this point significantly reduces the consumption of sodium carbonate and the precipitation efficiency.

[0058] As a preferred embodiment, since the lithium carbonate obtained by one-time evaporation concentration precipitation and sodium carbonate precipitation is of high quality, it can be used as a causticizing raw material with industrial-grade lithium carbonate. In step (4), the lithium carbonate obtained by cooling crystallization and sodium carbonate precipitation is returned to step (1) to replace at least part of the industrial lithium carbonate.

[0059] As a preferred embodiment, in step (4), the crystallized liquid is returned to step (1) to prepare slurry or combined with the carbonized liquid for processing, so as to achieve complete lithium recovery and lithium closed loop.

[0060] As a preferred embodiment, in step (1), the causticized slag is calcined at high temperature to obtain recycled quicklime and carbon dioxide;

[0061] Throughout the entire process, the calcination of the caustic slag and the pH adjustment for carbon removal both generate a considerable amount of carbon dioxide. As a preferred embodiment, this carbon dioxide can be fully collected and used in the carbonization step, achieving carbon dioxide gas recycling. The concentrated carbon dioxide is then used in the carbonization reaction in step (3). This can be achieved by collecting, compressing, and storing the carbon dioxide, and then using it in parallel with industrial-grade carbon dioxide in the carbonization process of step (3). In step (4), the carbon dioxide generated from pH adjustment is collected, concentrated, and returned to step (3) for the carbonization reaction.

[0062] As a preferred embodiment, when the CaO content in the recycled quicklime is ≥90wt.%, it is returned to step (1) as raw material, and when the CaO content in the recycled quicklime is <90wt.%, it is sold externally as building filler.

[0063] As a preferred embodiment, before high-temperature calcination, the causticized slag is washed with water to obtain washing slag and washing water. The washing slag is used for high-temperature calcination to regenerate quicklime, and the washing water is returned to step (1) to prepare slurry. On the one hand, lithium recovery can be achieved, and on the other hand, washing water can be recycled.

[0064] As a preferred embodiment, in step (4), the lithium content in the lithium carbonate obtained by cooling crystallization and sodium carbonate precipitation is 17-18.7 wt.%; and the lithium content in the sodium potassium salt is less than 0.3 wt.%.

[0065] As a specific implementation method that is optional, and as a conventional step in the art, in step (3), after carbonization, the carbonized liquid and precipitate can be obtained by centrifugation. The precipitate is washed to obtain wash water, and the washed solid is dried and crushed to obtain lithium carbonate. It is worth noting that, except for the solid-liquid separation in this step, the solid-liquid separation in other steps of the entire process (except for the two separations of sodium and potassium salts in step 4) will wash the solid phase, and the wash water can be returned to step (1) for preparing slurry. This is a conventional operation in the art.

[0066] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0067] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0068] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0069] Example 1:

[0070] 1.4 t of quicklime and 16 t of water, 1.5 t of industrial-grade lithium carbonate and 15 t of water were separately prepared into slurries, pre-dispersed, and then pumped together into a causticizing reactor for causticizing reaction at 85℃. After 2 hours of reaction, the mixture was filtered to obtain causticizing liquid and causticizing residue. The causticizing liquid was evaporated, concentrated, cooled, crystallized, and redissolved and filtered to obtain refined lithium hydroxide liquid. The evaporation and concentration temperature was 105℃, and the cooling and crystallization temperature was 40℃. The lithium content in the refined lithium hydroxide liquid was 9 g / L. Industrial carbon dioxide was introduced into the refined lithium hydroxide liquid for carbonation. Carbonation was stopped when the pH value reached 10. After centrifugation, filtration, drying and crushing, battery-grade lithium carbonate and carbonized liquid were obtained. The composition of battery-grade lithium carbonate is shown in Table 1, the lithium content of the carbonized liquid is 4.06 g / L, and other components are shown in Table 3.

[0071] Table 1. Composition analysis of battery-grade lithium carbonate products (unit: wt%)

[0072]

[0073] Example 2:

[0074] Two liters of the carbonized liquid from Example 1 were taken for a single evaporation experiment. The liquid was filtered and dried at evaporation concentration ratios of 2, 3, 4, and 5:1, respectively. The solid residue was analyzed, and the results are shown in Table 2. The results show that high-purity Li2CO3 for causticization can be obtained with a single evaporation concentration ratio between 2 and 3:1.

[0075] Table 2. Analysis of the composition of the solid phase precipitated at different evaporation ratios (unit: wt%)

[0076]

[0077] Example 3:

[0078] 6L of the carbonized liquid from Example 1 was subjected to a single evaporation and concentration process to obtain 2L of primary concentrate. The primary evaporation and concentration temperature was 105°C. After cooling to room temperature, the concentrate was filtered to obtain primary filter residue and primary filtrate. XRD analysis was performed on the primary filter residue. Figure 2 As shown, the results indicate that the phase is Li₂CO₃, without any impurities. The composition is shown in Table 4, and it can be used as a causticizing raw material mixed with industrial-grade lithium carbonate. 1 L of the primary filtrate was added to 90% concentrated sulfuric acid until the pH reached 7. A second evaporation and concentration process was then performed to obtain 0.5 L of secondary concentrate at 105℃. After cooling to room temperature, the concentrate was filtered to obtain secondary filter residue and secondary filtrate, the compositions of which are shown in Tables 2 and 3. Soda ash was added to the secondary filtrate to precipitate lithium, with the amount of soda ash being 1.05 times the theoretical amount for complete lithium precipitation. The filtrate was filtered to obtain lithium carbonate and a post-precipitation liquid. The post-precipitation liquid was then crystallized to precipitate sodium and potassium salts. The mother liquor was recycled. The intermediate liquid and solid phase compositions are shown in Tables 3 and 4.

[0079] Experimental results show that the battery-grade lithium carbonate product obtained by carbon dioxide carbonization has high purity, with all indicators exceeding national standards, and its magnetic material indicators far surpassing national standards. The carbonized liquid undergoes a two-stage evaporation and concentration method provided by this invention, achieving liquid-phase recycling and recovering lithium carbonate with a purity exceeding 95%. This recovered lithium carbonate can be directly used as raw material in the causticization step, while sodium and potassium salt impurities are discharged from the system, effectively recovering lithium. The overall lithium recovery rate is 99.1%, and the accumulation of impurities such as sodium and potassium is avoided.

[0080] Table 3. Composition analysis of intermediate liquid phase (unit: g / L)

[0081]

[0082] Table 4. Composition analysis of intermediate solid phase (wt%)

[0083]

[0084] Example 4:

[0085] Take 1L of the primary filtrate from Example 3, add 20% concentrated hydrochloric acid to adjust the pH to 6, and then perform a second evaporation and concentration to obtain 0.5L of secondary concentrate. The evaporation and concentration temperature is 105℃. After cooling to room temperature, filter to obtain secondary filter residue and secondary filtrate, the composition of which is shown in Tables 5 and 6. Add soda ash to the secondary filtrate to precipitate lithium. The amount of soda ash used is 1.1 times the theoretical amount of lithium to be completely precipitated. Filter to obtain lithium carbonate. Crystallize the lithium-precipitated liquid to obtain sodium potassium salt, the composition of which is shown in Tables 5 and 6.

[0086] Experimental results show that adjusting the pH value with hydrochloric acid can also fully recover lithium. Compared with using sulfuric acid, using hydrochloric acid can effectively reduce the lithium content in the secondary filter residue and sodium and potassium salts, and improve the lithium recovery rate, with a comprehensive lithium recovery rate of 99.5%.

[0087] Table 5. Composition analysis of intermediate liquid phase (unit: g / L)

[0088]

[0089] Table 6. Composition analysis of intermediate solid phase (wt%)

[0090]

[0091] Example 5:

[0092] The causticizing slag used in this embodiment is the product of the causticizing slag produced in Example 1 after water washing and drying. The causticizing slag is calcined at 950°C to obtain quicklime. The CaO content is tested and found to be 95 wt.%, which meets the standard for recycled quicklime and can be directly used for causticizing. The carbon dioxide produced in the reaction is compressed and introduced into a gas storage tank for carbonization.

[0093] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for producing battery-grade lithium carbonate via gas-liquid recycling, characterized in that, include: (1) Prepare a slurry with industrial grade lithium carbonate, water and quicklime and carry out a causticization reaction. After solid-liquid separation, obtain lithium hydroxide solution and causticization residue. (2) After evaporating and concentrating the lithium hydroxide solution, cool and crystallize it. Then, redissolve and finely filter the resulting crystals to obtain a refined lithium hydroxide solution. (3) Carbon dioxide is introduced into the lithium hydroxide refining solution to carry out a carbonization reaction. After carbonization, solid-liquid separation is carried out to obtain battery-grade lithium carbonate and carbonized liquid. (4) The carbonized liquid is subjected to first evaporation concentration and cooling crystallization, and filtered to obtain lithium carbonate and primary concentrate; wherein, the first evaporation concentration ratio is 2 to 3:1; the cooling crystallization temperature after the first evaporation concentration is 20 to 40°C; Acid is added to the primary concentrate to adjust the pH to 5-7, followed by a second evaporation concentration and cooling crystallization. The solution is then filtered to obtain sodium and potassium salts and a secondary concentrate. The cooling crystallization temperature after the second evaporation concentration is 20-40°C. Sodium carbonate is added to the secondary concentrate to precipitate lithium, resulting in lithium carbonate and a lithium-precipitated liquid. The lithium-precipitated liquid is then subjected to crystallization and solid-liquid separation to obtain sodium potassium salt and a crystallized liquid. The lithium content of the sodium potassium salt is less than 0.3 wt.%. In step (4), the crystallized liquid is returned to step (1) to prepare slurry or combined with the carbonized liquid for further processing.

2. The method for producing battery-grade lithium carbonate via gas-liquid recycling as described in claim 1, characterized in that, In step (1), the industrial lithium carbonate has a Li₂CO₃ content ≥ 98.5 wt.% and the quicklime has a CaO content ≥ 90 wt.%. The Li content of the obtained lithium hydroxide solution is 8.5–9.5 g / L.

3. The method for producing battery-grade lithium carbonate via gas-liquid recycling as described in claim 1, characterized in that, In step (1), the molar ratio of Li2CO3 to CaO in the slurry is 1:1.05 to 1.5, and the solid-liquid ratio is 1:8 to 12. The causticizing reaction is carried out at a temperature of 80–95°C, a stirring rate of 200–400 rpm, and a reaction time of 1–10 h.

4. The method for producing battery-grade lithium carbonate via gas-liquid recycling as described in claim 1, characterized in that, In step (2), the temperature of the steam for evaporation and concentration is 100-120°C, and the temperature for cooling and crystallization is 40-50°C. The lithium hydroxide solution has a Li content of 25–35 g / L; the refined lithium hydroxide solution has a Li content of 25–35 g / L.

5. The method for producing battery-grade lithium carbonate via gas-liquid recycling as described in claim 1, characterized in that, In step (3), the carbon dioxide is industrial-grade carbon dioxide; the temperature of the carbonization reaction is 20-80℃; and the final pH value of the carbonization reaction is 9.5-10.

5. The Li content of the resulting carbonized liquid is 2–6 g / L.

6. The method for producing battery-grade lithium carbonate via gas-liquid recycling as described in claim 1, characterized in that, In step (4), the temperature of the first evaporation and concentration is 100-120°C; The temperature of the second evaporation and concentration is 100-120°C, and the second evaporation and concentration ratio is 2-5:1; The acid is sulfuric acid or hydrochloric acid; the carbon dioxide generated by adjusting the pH value is collected, concentrated, and returned to step (3) for carbonization reaction.

7. The method for producing battery-grade lithium carbonate via gas-liquid recycling as described in claim 1, characterized in that, In step (4), the amount of sodium carbonate added is 1.05 to 1.1 times the theoretical amount required to achieve complete lithium precipitation in the secondary concentrate; In step (4), the lithium carbonate obtained from cooling crystallization and sodium carbonate precipitation is returned to step (1) to replace at least a portion of the industrial lithium carbonate.

8. The method for producing battery-grade lithium carbonate via gas-liquid recycling as described in claim 1, characterized in that, In step (1), the causticized slag is calcined at high temperature to obtain recycled quicklime and carbon dioxide; The carbon dioxide is concentrated and used for the carbonization reaction in step (3); when the CaO content in the recycled quicklime is ≥90wt.%, it is returned to step (1) as raw material, and when the CaO content in the recycled quicklime is <90wt.%, it is sold externally.

9. The method for producing battery-grade lithium carbonate via gas-liquid recycling as described in claim 8, characterized in that, Before high-temperature calcination, the causticized slag is washed with water to obtain washing slag and washing water. The washing slag is used for high-temperature calcination to regenerate quicklime, and the washing water is returned to step (1) for preparing slurry.

10. The method for producing battery-grade lithium carbonate via gas-liquid recycling as described in claim 1, characterized in that, In step (4), the lithium content in the lithium carbonate obtained by cooling crystallization and sodium carbonate precipitation is 17-18.7%.

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