Method for producing lithium carbonate by using lithium hydroxide mother liquor

Abstract

The invention discloses a method for producing lithium carbonate by using lithium hydroxide mother liquor. The method specifically comprises the following steps: step 1, roasting spodumene concentrate, and step 2, carrying out ball milling on the roasted spodumene; 3, mixing with sulfuric acid after ball milling, and roasting to generate lithium sulfate; 4, water is added for pulping and leaching, and a lithium sulfate solution is obtained; 5, adding caustic soda liquid and sodium carbonate into the solution to adjust the pH value, and filtering to remove impurities; step 6, evaporating and concentrating the purified solution to obtain a lithium sulfate finished solution; 7, mixing the finished liquid with liquid caustic soda to obtain conversion liquid; 8, introducing the conversion liquid into a freezing system to obtain frozen liquid and sodium sulfate decahydrate; step 9, evaporating and concentrating the frozen liquid, and performing centrifugal separation to obtain a crude product mother solution and a crude product lithium hydroxide; step 10, simultaneously pumping the crude product mother liquor and carbon dioxide gas into high-speed cutting reaction equipment to generate lithium carbonate solid particles and liquid; step 11, washing and drying the wet material to obtain a high-purity lithium carbonate product, and the method is simple and easy to implement and high in reaction efficiency.

Description

Technical Field

[0001] The present invention relates to a method for producing lithium carbonate, in particular to a method for producing lithium carbonate by using lithium hydroxide mother liquor, and belongs to the technical field of battery-grade lithium salt production. Background Art

[0002] In the process of producing lithium hydroxide, an evaporated centrifugal mother liquor will be generated. Since the mother liquor contains lithium, the general practice is to return the mother liquor to the system for reuse. Due to multiple recycling, K ions will be enriched in the system. When the concentration is greater than 25g / L, the potassium ions in the product lithium hydroxide will gradually exceed the standard, causing the product to be unqualified. Some companies will react this part of the mother liquor with carbon dioxide in a carbonization equipment, and then obtain battery-grade or high-purity lithium carbonate through hydrogenation, pyrolysis, centrifugation, and drying.

[0003] Patent CN110980775A discloses a method for producing multi-grade lithium carbonate by continuous carbonization. This method utilizes a multi-stage carbonization process, using carbon dioxide and a liquid feed to react in a multi-stage reactor. Carbon dioxide and lithium hydroxide can fully react, achieving continuous production of lithium carbonate. This production system boasts high production capacity, high production efficiency, low production costs, and stable product quality. Patent CN117361591A discloses a process for directly producing battery-grade lithium carbonate from lithium hydroxide circulating mother liquor. During the pretreatment of the lithium hydroxide circulating mother liquor, chemical precipitation, ion exchange, membrane separation, and boiling distillation are employed to remove impurities or harmful substances from the lithium hydroxide circulating mother liquor, thereby improving its purity. In the above technical processes, carbon dioxide reacts with the mother liquor through reverse contact, the reaction efficiency is low, the generated lithium carbonate particles are uneven, there is a phenomenon of inclusion, and impurity ions exist in the lithium carbonate crystals and are unevenly distributed. It is necessary to continue to add carbon dioxide to hydrogenate to generate lithium bicarbonate, and then filter and pyrolyze to regenerate clean lithium carbonate. During the hydrogenation process, carbon dioxide and lithium carbonate slurry react in reverse contact, and the reaction efficiency is less than 60%. The unreacted carbon dioxide needs to be collected, washed, compressed, and returned to the carbon dioxide system for reuse. The entire process has low reaction efficiency, high energy consumption, large equipment investment, and a large floor space.

[0004] Therefore, developing a method for producing lithium carbonate that can overcome the above defects has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for producing lithium carbonate from lithium hydroxide mother liquor, which is simple and easy to operate, has high reaction efficiency and reduces costs.

[0006] In order to solve the above technical problems, the present invention provides a method for producing lithium carbonate from lithium hydroxide mother liquor, which specifically comprises the following steps: Step 1: High temperature roasting The spodumene concentrate is roasted in a high temperature roasting device at 1000-1100°C to convert it from α-type to β-type; Step 2: Grind The calcined spodumene is ground into less than 200 meshes by a ball mill; Step 3: Acidification and Calcination The ground spodumene is mixed with sulfuric acid and then sent to an acidification roasting device at 250-300℃ for roasting to produce lithium sulfate; Step 4: Leaching The acidified and roasted clinker is added with water to prepare pulp and leach, so that lithium sulfate enters the solution to obtain a lithium sulfate solution; Step 5: Purification Adding liquid caustic soda and soda ash to the lithium sulfate solution to adjust the pH value, and filtering to remove impurities; Step 6: Evaporation and Concentration The purified lithium sulfate solution is evaporated and concentrated to obtain a lithium sulfate finished solution; Step 7: Conversion The lithium sulfate finished solution is mixed with liquid alkali to react to obtain a conversion solution containing lithium hydroxide; Step 8: Freeze Sodium Extraction The conversion liquid is passed into a freezing system to obtain a frozen liquid and sodium sulfate decahydrate; Step 9: Centrifuge The frozen liquid is concentrated by MVR evaporation and then centrifuged to obtain crude mother liquor and crude lithium hydroxide; Step 10: Carbonization and Separation The crude lithium hydroxide mother liquor and carbon dioxide gas are simultaneously pumped into a high-speed cutting reaction device. Inside the reactor, the lithium hydroxide and carbon dioxide fully contact and react with each other, and centrifugation is performed during the reaction to produce lithium carbonate solid particles and liquid. Under the action of centrifugal force, lithium carbonate solid particles are separated from the liquid in the drum of the high-speed cutting reaction equipment. The screw conveyor in the high-speed cutting reaction equipment pushes the solid particles to the slag discharge port of the drum, and the discharged solid is lithium carbonate wet material; Step 11: Wash and dry The wet lithium carbonate material is washed and dried to obtain a high-purity lithium carbonate product.

[0007] The technical solution further defined in the present invention is: Furthermore, in the aforementioned method for producing lithium carbonate using lithium hydroxide mother liquor, the acidification rate in step 3 is not less than 97%.

[0008] In the aforementioned method for producing lithium carbonate using lithium hydroxide mother liquor, in step 6, the lithium sulfate solution is evaporated and concentrated to a Li2O content of 35-55 g / L.

[0009] In the aforementioned method for producing lithium carbonate using lithium hydroxide mother liquor, carbon dioxide gas with a purity of 99.99% is used in step 10.

[0010] In the aforementioned method for producing lithium carbonate using lithium hydroxide mother liquor, the high-speed cutting reaction equipment in step 10 is a horizontal sedimentation centrifuge, and cutting teeth are arranged on the edges of the spiral blades in the horizontal sedimentation centrifuge.

[0011] Technical effect: The present invention uses a horizontal sedimentation centrifuge to simultaneously complete the carbonization and separation of crude lithium hydroxide mother liquor and carbon dioxide gas, integrating the carbonization reaction and solid-liquid separation in one reactor, simplifying the process, improving efficiency, reducing costs, meeting the needs of high-quality lithium carbonate production, and solving the problem that the reactor and separation equipment have independent structures and functions, making it difficult to achieve efficient coordination; At the same time, certain improvements are made to the horizontal decanter centrifuge. Cutting teeth are arranged on the edge of the spiral blades to improve the cutting effect, which is conducive to breaking up and cutting the crude lithium hydroxide. The carbon dioxide is also cut into a large number of small bubbles at high speed, which is more conducive to the contact reaction. The mother liquor enters the equipment through a tangential spiral to react with carbon dioxide, and lithium carbonate solid is produced under full contact. The solid particles form fine particles during the high-speed rotation process. The entire reaction process is efficient in gas and liquid mode, which makes the materials fully contact in the reaction equipment, improves the reaction efficiency, and has the advantages of large processing capacity, high separation efficiency, and high degree of automation.

[0012] In the aforementioned method for producing lithium carbonate using lithium hydroxide mother liquor, the drum speed in the high-speed cutting reaction equipment in step 10 is 3000 r / min, and the screw conveyor speed in the high-speed cutting reaction equipment is 2800 r / min.

[0013] The beneficial effects of the present invention are: The present invention adopts high-speed gas and liquid cutting technology to react carbon dioxide and mother liquor in an improved horizontal sedimentation centrifuge with a centrifugal function, without the need for large-scale reactors, centrifuges, and hydrogenation pyrolysis equipment. The carbonization reaction and solid-liquid separation are integrated in one reactor, simplifying the process, improving efficiency, reducing costs, and meeting the production needs of high-quality lithium carbonate. The present invention solves the problem that the structures and functions of the reactor and the separation equipment are independent and difficult to achieve efficient coordination. In addition, lithium hydroxide and carbon dioxide can fully contact and react in the centrifuge, and the volume of the gas and particles is reduced under the action of the cutting teeth, further improving the contact reaction, and greatly reducing the problem of insufficient reaction.

[0014] The high-speed cutting reaction equipment adopted in the present invention is a cutting reaction technology, which cuts carbon dioxide into a large number of fine bubbles at high speed, and allows the mother liquor to enter the equipment through a tangential spiral to react with carbon dioxide, producing lithium carbonate solid under full contact. The solid particles form fine particles during the high-speed rotation process to obtain a higher-level product. The entire reaction process is efficient in gas and liquid mode, and the materials are fully contacted in the reactor, thereby improving the reaction efficiency. It has the advantages of large processing capacity, high separation efficiency, and high degree of automation.

[0015] Compared with the prior art, the present invention also has the following advantages: (1) simplification of the process flow: the present invention integrates the reaction of lithium hydroxide conversion liquid with carbon dioxide and the solid-liquid separation process in a reactor with a centrifugal function, eliminating the material transfer link between the reactor and the separation equipment in the traditional process, simplifying the process flow, and no longer requiring separate carbonization, hydrogenation, pyrolysis and other processes, thereby reducing the equipment footprint and investment costs; (2) improvement of production efficiency: the high degree of automation can realize continuous production, reduce labor costs, and improve the stability and reliability of the production process; at the same time, the lithium hydroxide conversion liquid and carbon dioxide gas can fully contact and react, thereby improving the reaction efficiency and the generation rate of lithium carbonate.

[0016] The present invention adopts a process for producing lithium carbonate without hydrogenation and pyrolysis, which has high lithium yield, low energy consumption, low cost, and mature and reliable process; at the same time, it reduces the number of equipment and floor space, and lowers equipment investment and maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a flow chart of a method for producing lithium carbonate from lithium hydroxide mother liquor according to an embodiment of the present invention; Figure 2 A schematic diagram of a portion of the structure of a high-speed cutting reaction device used in a method for producing lithium carbonate from lithium hydroxide mother liquor according to an embodiment of the present invention; Figure 3 for Figure 2 Schematic diagram of the enlarged structure of part A; In the figure: 1-drum, 2-shaft, 3-spiral blade, 4-cutting teeth. DETAILED DESCRIPTION

[0018] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention. Example 1

[0019] This embodiment provides a method for producing lithium carbonate using lithium hydroxide mother liquor, the process is as follows Figure 1 As shown, the specific steps include: Step 1: High temperature roasting The spodumene concentrate is roasted at 1050℃ in a high temperature roasting device, and the structure changes from dense to loose, and the spodumene is converted from α type to β type; Step 2: Grind The calcined spodumene is ground into less than 200 meshes by a ball mill; Step 3: Acidification and Calcination The ground spodumene is mixed with excess sulfuric acid, the amount of sulfuric acid is 140% of the theoretical value, and then sent to the acidification roasting device at 280℃ for roasting to produce acid clinker of lithium sulfate, with an acidification rate of not less than 97%; Step 4: Leaching The acidified and roasted clinker is slurried with water to leach lithium sulfate into the solution, and filtered using a filter press to obtain a lithium sulfate solution; Step 5: Purification Liquid caustic soda and soda ash are added to the lithium sulfate solution to adjust the pH value, and impurity precipitation is removed using a precision filter in the prior art to remove impurities such as iron, calcium, and magnesium; Step 6: Evaporation and Concentration The purified lithium sulfate solution is evaporated and concentrated to a Li2O content of 35-55 g / L to obtain a lithium sulfate finished solution; Step 7: Conversion Add 50% liquid caustic soda to the finished lithium sulfate solution in a conversion tank to carry out a conversion reaction, and filter to obtain a conversion solution containing lithium hydroxide; Step 8: Freeze Sodium Extraction The conversion liquid is passed into a freezing system to obtain a frozen liquid and sodium sulfate decahydrate; Step 9: Centrifuge The frozen liquid is concentrated by MVR evaporation and then centrifuged to obtain crude mother liquor and crude lithium hydroxide; Step 10: Carbonization and Separation Crude lithium hydroxide mother liquor and 99.99% pure carbon dioxide gas are simultaneously pumped into an improved horizontal decanter centrifuge with a centrifugal function. The drum speed is set to 3000 r / min, the screw conveyor speed is 2800 r / min, the differential speed is 200 r / min, the reaction temperature is 25° C., and the reaction time is 10 minutes. Inside the reactor, the lithium hydroxide and carbon dioxide fully contact and react, and centrifugation is performed during the reaction to produce lithium carbonate solid particles and liquid. Under the action of centrifugal force, lithium carbonate solid particles are separated from the liquid in the drum, and the screw conveyor pushes the solid particles to the discharge port of the drum. The discharged solid is lithium carbonate wet material; It should be noted that the horizontal decanter centrifuge adopts the existing horizontal decanter centrifuge such as Figure 2 As shown, only part of the structure is shown in the figure, including a casing (not shown in the figure), a drum 1 is rotatably installed in the casing, the drum 1 includes a cylindrical sedimentation section and a truncated cone separation section, a screw conveyor is rotatably installed in the drum, the end of the cylindrical body of the drum 1 is provided with a liquid discharge port, the end of the truncated cone body is provided with a solid discharge port, the screw conveyor includes a rotating shaft 2 and a spiral blade 3 arranged outside the rotating shaft, the outermost edge of the spiral blade 3 is improved to a cutting tooth 4 as shown Figure 3 As shown, the cutting effect can be improved, which is conducive to breaking up and cutting the crude lithium hydroxide. It is also more conducive to the contact reaction by cutting the carbon dioxide into a large number of fine bubbles at high speed. The rotating shaft 2 and the drum 1 are both connected to the differential. One end of the rotating shaft 2 is provided with a feed pipe. The horizontal sedimentation centrifuge used in this embodiment only needs to meet the functions of mixing, cutting and centrifugation. The specific structure is not described in detail in this embodiment; Step 11: Washing and Drying The wet lithium carbonate material is placed into a washing and drying device, and then dried at 180°C for 2 hours to obtain a high-purity lithium carbonate product.

[0020] The process of producing lithium carbonate by the present invention does not require hydrogenation and pyrolysis, has high lithium yield, low energy consumption, low cost, and is mature and reliable. At the same time, the number of equipment and the floor space occupied are reduced, and the equipment investment and maintenance costs are lowered.

[0021] In addition to the above embodiments, the present invention may also have other implementations. Any technical solution formed by equivalent replacement or equivalent transformation falls within the scope of protection required by the present invention.

Claims

1. A method for producing lithium carbonate using lithium hydroxide mother liquor, characterized in that: The specific steps include: Step 1: High temperature roasting The spodumene concentrate is roasted in a high temperature roasting device at 1000-1100°C to convert it from α-type to β-type; Step 2: Grind The calcined spodumene is ground into less than 200 meshes by a ball mill; Step 3: Acidification and Calcination The ground spodumene is mixed with sulfuric acid and then sent to an acidification roasting device at 250-300℃ for roasting to produce lithium sulfate; Step 4: Leaching The acidified and roasted clinker is added with water to prepare pulp and leach, so that lithium sulfate enters the solution to obtain a lithium sulfate solution; Step 5: Purification Adding liquid caustic soda and soda ash to the lithium sulfate solution to adjust the pH value, and filtering to remove impurities; Step 6: Evaporation and Concentration The purified lithium sulfate solution is evaporated and concentrated to obtain a lithium sulfate finished solution; Step 7: Conversion The lithium sulfate finished solution is mixed with liquid alkali to react to obtain a conversion solution containing lithium hydroxide; Step 8: Freeze Sodium Extraction Passing the conversion liquid into a freezing system to obtain a frozen liquid and sodium sulfate decahydrate; Step 9: Centrifuge The frozen liquid is concentrated by MVR evaporation and then centrifuged to obtain a crude mother liquor and crude lithium hydroxide; Step 10: Carbonization and Separation The crude lithium hydroxide mother liquor and carbon dioxide gas are simultaneously pumped into a high-speed cutting reaction device. Inside the reactor, the lithium hydroxide and carbon dioxide come into contact and react with each other, and centrifugation is performed during the reaction to produce lithium carbonate solid particles and liquid. Under the action of centrifugal force, lithium carbonate solid particles are separated from the liquid in the high-speed cutting reaction equipment, and the discharged solid is lithium carbonate wet material; Step 11: Wash and dry The wet lithium carbonate material is washed and dried to obtain a high-purity lithium carbonate product.

2. The method for producing lithium carbonate from lithium hydroxide mother liquor according to claim 1, wherein: The acidification rate in step 3 is not less than 97%.

3. The method for producing lithium carbonate from lithium hydroxide mother liquor according to claim 1, wherein: In step 6, the lithium sulfate solution is evaporated and concentrated to a Li2O content of 35-55 g / L.

4. The method for producing lithium carbonate from lithium hydroxide mother liquor according to claim 1, wherein: In step 10, carbon dioxide gas with a purity of 99.99% is used.

5. The method for producing lithium carbonate from lithium hydroxide mother liquor according to claim 1, wherein: The high-speed cutting reaction equipment in step 10 is a horizontal decanter centrifuge, and cutting teeth are arranged on the edges of the spiral blades in the horizontal decanter centrifuge.

6. The method for producing lithium carbonate from lithium hydroxide mother liquor according to claim 5, wherein: The rotating drum speed of the horizontal decanter centrifuge is 3000 r / min, and the rotating screw conveyor speed of the horizontal decanter centrifuge is 2800 r / min.

Images