A system and method for selectively extracting lithium from aluminum electrolyte waste residue and simultaneously preparing molecular sieves

Abstract

The present application relates to solid waste resource utilization and environmental protection technical field, disclose a kind of from aluminum electrolyte waste slag selective extraction lithium and synchronous preparation molecular sieve system and method, the method of the present application includes: after aluminum electrolyte waste slag is broken and ground, mix with dilute sulfuric acid acidolysis, obtain acidolysis slurry;Calcium carbonate is added to the acidolysis slurry, and pH is adjusted to 3.0-4.0, so that aluminum ion and fluoride ion are precipitated as cryolite, and filtration is carried out to obtain lithium-containing filtrate and cryolite precipitate residue;Lithium carbonate is obtained by adding sodium carbonate to lithium-containing filtrate and precipitating;Cryolite precipitate residue is mixed with sodium hydroxide solution to alkali solution, so that cryolite is converted into sodium fluoride and sodium metaaluminate, and molecular sieve product is obtained by adding silicon source again;The present application also discloses a system for realizing the above method.The present application realizes efficient and selective extraction of lithium from aluminum electrolyte waste slag, and simultaneously converts aluminum, fluorine and silicon in the waste slag into molecular sieve, which is suitable for resource disposal of hazardous waste in aluminum industry.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization and environmental protection technology, specifically to a system and method for selectively extracting lithium from aluminum electrolyte waste residue and simultaneously preparing molecular sieves. Background Technology

[0002] The aluminum electrolysis industry generates a large amount of hazardous waste such as waste electrolyte, overhaul slag, and carbon slag during production, with an annual output exceeding 5 million tons. The fluoride content in this type of waste slag is as high as 30%-60%, and lithium exists in the form of lithium fluoride and lithium cryolite. The lithium content is enriched to 1.0%-2.7%, which is comparable to the grade of natural low-grade lithium ore, and has significant recovery value.

[0003] Currently, the main technologies for the disposal of aluminum electrolyte waste residue include safe landfill and acid leaching. Although safe landfill is simple to operate, soluble fluorides and cyanides are prone to seepage and pollution of soil and groundwater, resulting in the complete waste of valuable elements such as lithium, aluminum, and fluorine. The cost of landfilling per ton of residue is high, placing a heavy burden on enterprises. In the acid leaching route, existing technologies usually use strong acids to leach all metal elements at once, resulting in aluminum, lithium, sodium, and fluorine entering the solution at the same time. Subsequent separation processes are complex, and the consumption of acid and alkali is large. Furthermore, fluorine is prone to escape in the form of hydrogen fluoride under acidic conditions, causing secondary pollution, making it difficult to achieve the resource utilization of aluminum, fluorine, and silicon. Summary of the Invention

[0004] The purpose of this invention is to provide a system and method for selectively extracting lithium from aluminum electrolyte waste and simultaneously preparing molecular sieves, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for selectively extracting lithium from aluminum electrolyte waste and simultaneously preparing molecular sieves, comprising the following steps: S1. After crushing and grinding the aluminum electrolyte waste residue to a particle size of less than 200 mesh, mix it with dilute sulfuric acid with a mass concentration of 10%-20% at a solid-liquid ratio of 1:3-1:6, and stir and acidify at 60-90℃ for 1-3 hours to obtain acid slurry. S2. Add calcium carbonate to the acid hydrolysis slurry in batches to adjust the pH of the slurry to 3.0-4.0, so that aluminum ions and fluoride ions co-precipitate into cryolite, while lithium ions remain in the liquid phase. After filtration, separate the lithium-containing filtrate and cryolite precipitate residue. S3. Add sodium carbonate to the lithium-containing filtrate, adjust the pH to 8.0-9.0, precipitate lithium ions at 70-90℃ to obtain lithium carbonate, and obtain lithium carbonate product after solid-liquid separation. The remaining liquid is the lithium precipitation liquid. S4. Mix cryolite precipitate residue with sodium hydroxide solution of 10%-25% by mass at a solid-liquid ratio of 1:2-1:5, and react with alkaline solution at 90-120℃ for 2-5 hours to convert cryolite into sodium fluoride and sodium aluminate to obtain alkaline slurry. S5. Add silicon source to alkaline slurry, adjust silicon-aluminum molar ratio to 1.5-2.5, crystallize at 80-120℃ for 4-10 hours, and obtain molecular sieve product after solid-liquid separation, washing and drying.

[0006] As a preferred technical solution of the present invention, in step S1, the solid-liquid ratio of aluminum electrolyte waste residue to dilute sulfuric acid is 1:3-1:6, the mass concentration of dilute sulfuric acid is 10%-20%, the acidolysis reaction temperature is 60-90℃, and the reaction time is 1-3 hours. Furthermore, at least one of the following control methods is executed in step S1: Method 1: During the acid hydrolysis reaction, the stirring speed is 150-300 rpm. Method 2: The acid hydrolysis reaction is carried out in two stages. The first stage is carried out at 60-70℃ for 0.5-1 hour, and the second stage is carried out at 80-90℃ for 0.5-2 hours. Method 3: Add ammonium sulfate to dilute sulfuric acid. The amount of ammonium sulfate added is 0.5%-2% of the mass of aluminum electrolyte waste residue, which is used to suppress the escape of hydrogen fluoride gas. Method 4: The acidolysis reaction is carried out in a closed reactor and connected to a hydrogen fluoride absorption device, which contains a sodium hydroxide solution.

[0007] As a preferred technical solution of the present invention, in step S3, the lithium precipitation liquid is returned to step S1 for preparing dilute sulfuric acid after evaporation and concentration, or returned to step S4 for preparing sodium hydroxide solution. Furthermore, at least one of the following operations is performed in step S3: Operation 1: Before adding sodium carbonate, add hydrogen peroxide to the lithium-containing filtrate. The amount of hydrogen peroxide added is 0.1%-0.5% of the volume of the lithium-containing filtrate, which is used to oxidize and remove organic impurities. Operation 2: While adding sodium carbonate, lithium carbonate seed crystals are added simultaneously. The amount of seed crystals added is 0.5%-2% of the expected lithium carbonate yield, and the seed crystal particle size is 5-20 micrometers. Operation 3: The lithium carbonate precipitation reaction is carried out by adding sodium carbonate in two stages. The first time, sodium carbonate is added to adjust the pH value to 7.0-7.5, and the reaction is stirred for 0.5 hours. The second time, sodium carbonate is added to adjust the pH value to 8.0-9.0, and the reaction is continued for 1 hour. Operation 4: The lithium precipitation reaction temperature is 70-90℃. After the reaction is completed, age at room temperature for 1-3 hours before solid-liquid separation.

[0008] As a preferred embodiment of the present invention, in step S4, the mass concentration of the sodium hydroxide solution is 10%-25%, the solid-liquid ratio of the cryolite precipitate to the sodium hydroxide solution is 1:2-1:5, the alkaline dissolution reaction temperature is 90-120℃, and the reaction time is 2-5 hours. Furthermore, at least one of the following reinforcement measures is performed in step S4: Enhancement measure 1: The alkaline dissolution reaction is carried out in a high-pressure reactor at a pressure of 0.2-0.5 MPa; Enhancement measure 2: Add sodium chloride to the alkaline dissolution reaction system. The amount of sodium chloride added is 5%-15% of the mass of the cryolite precipitate, which is used to promote the exchange and dissociation of sodium ions in the cryolite. Enhancement measure three: During the alkaline dissolution reaction, a protective gas is introduced. The protective gas is nitrogen or argon, and the gas flow rate is 0.5-2 liters / minute to prevent interference from carbon dioxide in the air. Enhancement Measure 4: The alkali dissolution reaction adopts microwave-assisted heating with a microwave power of 300-800 watts and a heating time of 10-30 minutes, so that the cryolite precipitate is rapidly heated to the reaction temperature and then switched to conventional heat preservation.

[0009] As a preferred technical solution of the present invention, in step S5, the silicon source is sodium silicate or silica sol, and the mother liquor obtained after solid-liquid separation after crystallization is returned to step S4 for recycling after sodium hydroxide is added. Furthermore, at least one of the following control measures is performed in step S5: Control method 1: When adding a silicon source to the alkaline slurry, add a template agent, which is tetrapropylammonium hydroxide or tetraethylammonium hydroxide. The amount of template agent added is 0.1-0.5 times the molar amount of silicon dioxide in the silicon source. Control method two: The crystallization reaction adopts a segmented heating method. The first stage is crystallization at 80-90℃ for 2-4 hours, and the second stage is heated to 100-120℃ to continue crystallization for 2-6 hours. Control method three: Before the crystallization reaction, add a crystallization accelerator to the mixture of alkaline solution and silicon source. The crystallization accelerator is vinylidene fluoride or polyethylene glycol, and the amount added is 0.05%-0.2% of the mass of the mixture. Control method four: After the crystallization reaction is completed, the crystallization slurry is rapidly cooled to room temperature at a rate of 5-15℃ / minute, and then solid-liquid separation is performed.

[0010] A system for selectively extracting lithium from aluminum electrolyte waste and simultaneously preparing molecular sieves to implement the method described in any one of the above, comprising: The acidolysis unit is used to crush and grind aluminum electrolyte waste residue and mix it with dilute sulfuric acid to carry out an acidolysis reaction to obtain an acidolysis slurry. The first pH adjustment unit is connected to the outlet of the acid hydrolysis unit. It is used to add calcium carbonate to the acid hydrolysis slurry and adjust the pH value to 3.0-4.0, so that aluminum ions and fluoride ions precipitate in the form of cryolite, while lithium ions remain in the solution. The first filtration unit is connected to the outlet of the first pH adjustment unit and filters the slurry output by the first pH adjustment unit to obtain lithium-containing filtrate and cryolite precipitate. The lithium precipitation unit is connected to the lithium-containing filtrate outlet of the first filtration unit. It is used to add sodium carbonate to the lithium-containing filtrate and adjust the pH value to 8.0-9.0, so that lithium ions precipitate in the form of lithium carbonate. The second filtration unit is connected to the outlet of the lithium precipitation unit and performs solid-liquid separation on the slurry output from the lithium precipitation unit to obtain lithium carbonate product and lithium precipitation liquid. The alkali dissolution unit is connected to the cryolite precipitate outlet of the first filtration unit. It is used to mix the cryolite precipitate with sodium hydroxide solution and carry out an alkali dissolution reaction under heating conditions, so that the cryolite decomposes to generate sodium fluoride and sodium aluminate, and obtains alkali dissolution slurry. The crystallization unit, connected to the outlet of the alkali dissolution unit, is used to add a silicon source to the alkali dissolution slurry, adjust the silicon-aluminum molar ratio to 1.5-2.5, and crystallize at 80-120℃ for 4-10 hours to obtain a crystallized slurry. The third filtration unit is connected to the outlet of the crystallization unit to perform solid-liquid separation on the crystallization slurry, obtaining molecular sieve products and crystallization mother liquor.

[0011] As a preferred embodiment of the present invention, the system further includes: An evaporation and concentration unit is connected to the lithium precipitation liquid outlet of the second filtration unit and is used to evaporate and concentrate the lithium precipitation liquid. The first pipeline connects the concentrated liquid outlet of the evaporation and concentration unit to the dilute sulfuric acid inlet of the acidolysis unit, and is used to return the concentrated liquid to the acidolysis unit to prepare dilute sulfuric acid. The second pipeline connects the concentrated liquid outlet of the evaporation and concentration unit to the sodium hydroxide solution inlet of the alkali dissolution unit, and is used to return the concentrated liquid to the alkali dissolution unit to prepare sodium hydroxide solution. The acid hydrolysis unit is equipped with a stirrer, and the stirrer speed is controlled within the range of 150-300 rpm. The acid hydrolysis unit is equipped with a heating jacket, and hot water or steam is circulated inside the heating jacket; The top of the acidolysis unit is connected to a hydrogen fluoride absorption tower, which is filled with sodium hydroxide solution.

[0012] As a preferred technical solution of the present invention, the alkali dissolution unit includes a heating jacket and a temperature controller. The heating jacket is sleeved on the outer wall of the reaction vessel of the alkali dissolution unit, and the temperature controller is connected to the heating jacket to control the alkali dissolution reaction temperature at 90-120°C. The alkali dissolution unit is a high-pressure reactor, which is equipped with a pressure controller with a pressure control range of 0.2-0.5 MPa. The high-pressure reactor is equipped with an agitator, which adopts an anchor or paddle structure. A microwave generator is installed on the outer wall or inside the high-pressure reactor, with a power of 300-800 watts.

[0013] As a preferred embodiment of the present invention, the system further includes: The mother liquor recycling pipeline connects the crystallization mother liquor outlet of the third filtration unit and the inlet of the alkali dissolution unit, and is used to return the crystallization mother liquor to the alkali dissolution unit for recycling after adding sodium hydroxide; The crystallization unit is equipped with a segmented temperature controller, which is used to control the crystallization unit to be kept at 80-90℃ for 2-4 hours and at 100-120℃ for 2-6 hours in sequence. The crystallization unit is equipped with a cooling coil, which is circulated with cooling water at a cooling rate of 5-15℃ / minute.

[0014] As a preferred embodiment of the present invention, the acid hydrolysis unit includes a crusher, a grinder, and an acid hydrolysis reactor connected in sequence. The discharge port of the crusher is connected to the inlet of the grinder, and the discharge port of the grinder is connected to the solid inlet of the acid hydrolysis reactor. The acid hydrolysis reactor is equipped with a dilute sulfuric acid inlet, a stirrer, and a heating jacket. The lithium deposition unit includes a sodium carbonate storage tank, a hydrogen peroxide storage tank, and a seed crystal feeder. The sodium carbonate storage tank is connected to the reaction vessel of the lithium deposition unit via a metering pump. The hydrogen peroxide storage tank is connected to the reaction vessel of the lithium deposition unit via a pipeline. The outlet of the seed crystal feeder extends into the reaction vessel of the lithium deposition unit. The outlet of the second filtration unit is connected to the inlet of the evaporation and concentration unit, which is equipped with a condensate outlet and a concentrate outlet.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention achieves efficient separation of lithium from aluminum and fluoride by means of selective acid leaching and precise pH adjustment by calcium carbonate, which allows aluminum and fluoride ions to co-precipitate into cryolite at a pH of 3.0-4.0, while lithium ions remain in the liquid phase. This avoids the subsequent separation difficulties caused by traditional strong acid leaching.

[0016] 2. This invention converts the separated cryolite precipitate residue into sodium fluoride and sodium aluminate through alkaline dissolution, and then adds silicon source to crystallize and synthesize into molecular sieve products, so that the aluminum, fluorine and silicon components in the waste residue are transformed into high-value-added porous materials, which completely changes the resource waste mode of traditional landfill or simple acid leaching.

[0017] 3. In the acidolysis stage, the present invention effectively suppresses the escape of hydrogen fluoride gas by adding ammonium sulfate, sealing the reaction, and absorbing hydrogen fluoride; in the alkaline dissolution stage, the invention ensures the environmental friendliness of the process by introducing a protective gas to prevent carbon dioxide interference.

[0018] 4. In this invention, the lithium precipitation liquid is evaporated and concentrated and then reused in the acidolysis unit to prepare dilute sulfuric acid and in the alkali dissolution unit to prepare sodium hydroxide solution. At the same time, the crystallization mother liquor is replenished with sodium hydroxide and returned to the alkali dissolution unit for recycling, realizing the full-process recycling of water, acid and alkali, which greatly reduces reagent consumption and wastewater discharge.

[0019] 5. This invention achieves selective lithium extraction and simultaneous molecular sieve preparation in the same device through system integration and process coupling. The process is short and has good operational continuity, providing a complete technical solution for the full resource utilization of aluminum electrolyte waste residue. It is suitable for the large-scale disposal and resource recovery of hazardous waste in the aluminum industry. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall process of a method for selectively extracting lithium from aluminum electrolyte waste residue and simultaneously preparing molecular sieves according to the present invention; Figure 2 This is a system structural framework diagram of the present invention for selectively extracting lithium from aluminum electrolyte waste and simultaneously preparing molecular sieves. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1 like Figure 1 As shown, this invention provides a method for selectively extracting lithium from aluminum electrolyte waste and simultaneously preparing molecular sieves, comprising the following steps: S1. After crushing and grinding the aluminum electrolyte waste residue to a particle size of less than 200 mesh, mix it with dilute sulfuric acid with a mass concentration of 10%-20% at a solid-liquid ratio of 1:3-1:6, and stir and acidify at 60-90℃ for 1-3 hours to obtain acid slurry. S2. Add calcium carbonate to the acid hydrolysis slurry in batches to adjust the pH of the slurry to 3.0-4.0, so that aluminum ions and fluoride ions co-precipitate into cryolite, while lithium ions remain in the liquid phase. After filtration, separate the lithium-containing filtrate and cryolite precipitate residue. S3. Add sodium carbonate to the lithium-containing filtrate, adjust the pH to 8.0-9.0, precipitate lithium ions at 70-90℃ to obtain lithium carbonate, and obtain lithium carbonate product after solid-liquid separation. The remaining liquid is the lithium precipitation liquid. S4. Mix cryolite precipitate residue with sodium hydroxide solution of 10%-25% by mass at a solid-liquid ratio of 1:2-1:5, and react with alkaline solution at 90-120℃ for 2-5 hours to convert cryolite into sodium fluoride and sodium aluminate to obtain alkaline slurry. S5. Add silicon source to alkaline slurry, adjust silicon-aluminum molar ratio to 1.5-2.5, crystallize at 80-120℃ for 4-10 hours, and obtain molecular sieve product after solid-liquid separation, washing and drying.

[0023] Furthermore, in step S1, the solid-liquid ratio of aluminum electrolyte waste residue to dilute sulfuric acid is 1:3-1:6, the mass concentration of dilute sulfuric acid is 10%-20%, the acidolysis reaction temperature is 60-90℃, and the reaction time is 1-3 hours. Furthermore, at least one of the following control methods is executed in step S1: Method 1: During the acid hydrolysis reaction, the stirring speed is 150-300 rpm. Method 2: The acid hydrolysis reaction is carried out in two stages. The first stage is carried out at 60-70℃ for 0.5-1 hour, and the second stage is carried out at 80-90℃ for 0.5-2 hours. Method 3: Add ammonium sulfate to dilute sulfuric acid. The amount of ammonium sulfate added is 0.5%-2% of the mass of aluminum electrolyte waste residue, which is used to suppress the escape of hydrogen fluoride gas. Method 4: The acidolysis reaction is carried out in a closed reactor and connected to a hydrogen fluoride absorption device, which contains a sodium hydroxide solution.

[0024] Furthermore, in step S3, the lithium precipitation liquid is evaporated and concentrated and then returned to step S1 for the preparation of dilute sulfuric acid, or returned to step S4 for the preparation of sodium hydroxide solution. Furthermore, at least one of the following operations is performed in step S3: Operation 1: Before adding sodium carbonate, add hydrogen peroxide to the lithium-containing filtrate. The amount of hydrogen peroxide added is 0.1%-0.5% of the volume of the lithium-containing filtrate, which is used to oxidize and remove organic impurities. Operation 2: While adding sodium carbonate, lithium carbonate seed crystals are added simultaneously. The amount of seed crystals added is 0.5%-2% of the expected lithium carbonate yield, and the seed crystal particle size is 5-20 micrometers. Operation 3: The lithium carbonate precipitation reaction is carried out by adding sodium carbonate in two stages. The first time, sodium carbonate is added to adjust the pH value to 7.0-7.5, and the reaction is stirred for 0.5 hours. The second time, sodium carbonate is added to adjust the pH value to 8.0-9.0, and the reaction is continued for 1 hour. Operation 4: The lithium precipitation reaction temperature is 70-90℃. After the reaction is completed, age at room temperature for 1-3 hours before solid-liquid separation.

[0025] Furthermore, in step S4, the mass concentration of the sodium hydroxide solution is 10%-25%, the solid-liquid ratio of the cryolite precipitate to the sodium hydroxide solution is 1:2-1:5, the alkaline dissolution reaction temperature is 90-120℃, and the reaction time is 2-5 hours. Furthermore, at least one of the following reinforcement measures is performed in step S4: Enhancement measure 1: The alkaline dissolution reaction is carried out in a high-pressure reactor at a pressure of 0.2-0.5 MPa; Enhancement measure 2: Add sodium chloride to the alkaline dissolution reaction system. The amount of sodium chloride added is 5%-15% of the mass of the cryolite precipitate, which is used to promote the exchange and dissociation of sodium ions in the cryolite. Enhancement measure three: During the alkaline dissolution reaction, a protective gas is introduced. The protective gas is nitrogen or argon, and the gas flow rate is 0.5-2 liters / minute to prevent interference from carbon dioxide in the air. Enhancement Measure 4: The alkali dissolution reaction adopts microwave-assisted heating with a microwave power of 300-800 watts and a heating time of 10-30 minutes, so that the cryolite precipitate is rapidly heated to the reaction temperature and then switched to conventional heat preservation.

[0026] Furthermore, in step S5, the silicon source is sodium silicate or silica sol, and the mother liquor obtained after solid-liquid separation after crystallization is returned to step S4 for recycling after sodium hydroxide is added. Furthermore, at least one of the following control measures is performed in step S5: Control method 1: When adding a silicon source to the alkaline slurry, add a template agent, which is tetrapropylammonium hydroxide or tetraethylammonium hydroxide. The amount of template agent added is 0.1-0.5 times the molar amount of silicon dioxide in the silicon source. Control method two: The crystallization reaction adopts a segmented heating method. The first stage is crystallization at 80-90℃ for 2-4 hours, and the second stage is heated to 100-120℃ to continue crystallization for 2-6 hours. Control method three: Before the crystallization reaction, add a crystallization accelerator to the mixture of alkaline solution and silicon source. The crystallization accelerator is vinylidene fluoride or polyethylene glycol, and the amount added is 0.05%-0.2% of the mass of the mixture. Control method four: After the crystallization reaction is completed, the crystallization slurry is rapidly cooled to room temperature at a rate of 5-15℃ / minute, and then solid-liquid separation is performed.

[0027] like Figure 2 As shown, the present invention also provides a system for selectively extracting lithium from aluminum electrolyte waste and simultaneously preparing molecular sieves for implementing any of the above methods, comprising: The acidolysis unit is used to crush and grind aluminum electrolyte waste residue and mix it with dilute sulfuric acid to carry out an acidolysis reaction to obtain an acidolysis slurry. The first pH adjustment unit is connected to the outlet of the acid hydrolysis unit. It is used to add calcium carbonate to the acid hydrolysis slurry and adjust the pH value to 3.0-4.0, so that aluminum ions and fluoride ions precipitate in the form of cryolite, while lithium ions remain in the solution. The first filtration unit is connected to the outlet of the first pH adjustment unit and filters the slurry output by the first pH adjustment unit to obtain lithium-containing filtrate and cryolite precipitate. The lithium precipitation unit is connected to the lithium-containing filtrate outlet of the first filtration unit. It is used to add sodium carbonate to the lithium-containing filtrate and adjust the pH value to 8.0-9.0, so that lithium ions precipitate in the form of lithium carbonate. The second filtration unit is connected to the outlet of the lithium precipitation unit and performs solid-liquid separation on the slurry output from the lithium precipitation unit to obtain lithium carbonate product and lithium precipitation liquid. The alkali dissolution unit is connected to the cryolite precipitate outlet of the first filtration unit. It is used to mix the cryolite precipitate with sodium hydroxide solution and carry out an alkali dissolution reaction under heating conditions, so that the cryolite decomposes to generate sodium fluoride and sodium aluminate, and obtains alkali dissolution slurry. The crystallization unit, connected to the outlet of the alkali dissolution unit, is used to add a silicon source to the alkali dissolution slurry, adjust the silicon-aluminum molar ratio to 1.5-2.5, and crystallize at 80-120℃ for 4-10 hours to obtain a crystallized slurry. The third filtration unit is connected to the outlet of the crystallization unit to perform solid-liquid separation on the crystallization slurry, obtaining molecular sieve products and crystallization mother liquor.

[0028] Furthermore, the system also includes: An evaporation and concentration unit is connected to the lithium precipitation liquid outlet of the second filtration unit and is used to evaporate and concentrate the lithium precipitation liquid. The first pipeline connects the concentrated liquid outlet of the evaporation and concentration unit to the dilute sulfuric acid inlet of the acidolysis unit, and is used to return the concentrated liquid to the acidolysis unit to prepare dilute sulfuric acid. The second pipeline connects the concentrated liquid outlet of the evaporation and concentration unit to the sodium hydroxide solution inlet of the alkali dissolution unit, and is used to return the concentrated liquid to the alkali dissolution unit to prepare sodium hydroxide solution. The acid hydrolysis unit is equipped with a stirrer, and the stirrer speed is controlled within the range of 150-300 rpm. The acid hydrolysis unit is equipped with a heating jacket, and hot water or steam is circulated inside the heating jacket; The top of the acidolysis unit is connected to a hydrogen fluoride absorption tower, which is filled with sodium hydroxide solution.

[0029] Furthermore, the alkali dissolution unit includes a heating jacket and a temperature controller. The heating jacket is fitted onto the outer wall of the reaction vessel of the alkali dissolution unit, and the temperature controller is connected to the heating jacket to control the alkali dissolution reaction temperature at 90-120℃. The alkali dissolution unit is a high-pressure reactor, which is equipped with a pressure controller with a pressure control range of 0.2-0.5 MPa. The high-pressure reactor is equipped with an agitator, which adopts an anchor or paddle structure. A microwave generator is installed on the outer wall or inside the high-pressure reactor, with a power of 300-800 watts.

[0030] Furthermore, the system also includes: The mother liquor recycling pipeline connects the crystallization mother liquor outlet of the third filtration unit and the inlet of the alkali dissolution unit, and is used to return the crystallization mother liquor to the alkali dissolution unit for recycling after adding sodium hydroxide; The crystallization unit is equipped with a segmented temperature controller, which is used to control the crystallization unit to be kept at 80-90℃ for 2-4 hours and at 100-120℃ for 2-6 hours in sequence. The crystallization unit is equipped with a cooling coil, which is circulated with cooling water at a cooling rate of 5-15℃ / minute.

[0031] Furthermore, the acid hydrolysis unit includes a crusher, a grinder, and an acid hydrolysis reactor connected in sequence. The discharge port of the crusher is connected to the feed port of the grinder, and the discharge port of the grinder is connected to the solid feed port of the acid hydrolysis reactor. The acid hydrolysis reactor is equipped with a dilute sulfuric acid inlet, a stirrer, and a heating jacket. The lithium deposition unit includes a sodium carbonate storage tank, a hydrogen peroxide storage tank, and a seed crystal feeder. The sodium carbonate storage tank is connected to the reaction vessel of the lithium deposition unit via a metering pump. The hydrogen peroxide storage tank is connected to the reaction vessel of the lithium deposition unit via a pipeline. The outlet of the seed crystal feeder extends into the reaction vessel of the lithium deposition unit. The outlet of the second filtration unit is connected to the inlet of the evaporation and concentration unit, which is equipped with a condensate outlet and a concentrate outlet.

[0032] Example 2 Taking the waste electrolyte generated by an aluminum electrolysis company as an example, the waste residue contains 1.8% lithium by mass, 45% fluoride by mass, and 20% aluminum by mass. The system of the present invention is used to selectively extract lithium and simultaneously prepare molecular sieves. The specific implementation process is as follows.

[0033] Step S1: The aluminum electrolyte waste residue is fed into the acidolysis unit, which includes a crusher, a grinder, and an acidolysis reactor connected in sequence. The crusher crushes the waste residue to less than 10 mm, and the grinder further grinds it to a particle size of less than 200 mesh. The ground waste residue powder is fed into the acidolysis reactor with 15% dilute sulfuric acid at a solid-liquid ratio of 1:4. The acidolysis reactor is equipped with a stirrer, and the stirring speed is controlled at 220 rpm. The acidolysis reactor is heated to 75°C through a heating jacket and reacted for 2 hours to obtain an acidolysis slurry. The top of the acidolysis reactor is connected to a hydrogen fluoride absorption tower, which contains sodium hydroxide solution to absorb the hydrogen fluoride gas that escapes during the reaction.

[0034] Step S2: The acid-hydrolyzed slurry enters the first pH adjustment unit, where calcium carbonate is added in batches to gradually adjust the pH value of the slurry to 3.5. Under this pH condition, aluminum ions and fluoride ions in the slurry co-precipitate to form cryolite precipitate, while lithium ions, due to their high solubility under acidic conditions, remain in the liquid phase. The slurry output from the first pH adjustment unit enters the first filtration unit for filtration, separating the lithium-containing filtrate and cryolite precipitate residue.

[0035] Step S3: The lithium-containing filtrate enters the lithium precipitation unit, which is equipped with a hydrogen peroxide storage tank. First, hydrogen peroxide is added to the lithium-containing filtrate at a volume of 0.3% of the filtrate volume to oxidize and remove residual organic impurities. Then, sodium carbonate is added to the filtrate through a sodium carbonate storage tank, while lithium carbonate seeds with a particle size of 10 micrometers are added through a seed feeder at a volume of 1% of the expected lithium carbonate yield. Sodium carbonate is added in two stages. After the first addition, the pH is adjusted to 7.2 and the reaction is stirred for 0.5 hours. After the second addition, the pH is adjusted to 8.5 and the reaction is continued at 80°C for 1 hour. After the reaction, the mixture is aged at room temperature for 2 hours and then sent to the second filtration unit for solid-liquid separation to obtain lithium carbonate product and the lithium precipitation liquid. The overall lithium extraction rate is found to be over 92%.

[0036] Step S4: The cryolite precipitate separated from the first filtration unit enters the alkali dissolution unit, which is a high-pressure reactor. The pressure controller is set to a reaction pressure of 0.3 MPa. A 18% sodium hydroxide solution is added to the high-pressure reactor, with a solid-liquid ratio of 1:3 between the cryolite precipitate and the sodium hydroxide solution. Sodium chloride is added to the reaction system at a rate of 10% of the mass of the cryolite precipitate to promote the exchange and dissociation of sodium ions in the cryolite. During the alkali dissolution reaction, nitrogen gas is introduced from the bottom of the high-pressure reactor as a protective gas at a flow rate of 1 L / min to prevent carbon dioxide from entering the reaction system and interfering with the reaction. A microwave generator with a microwave power of 500 W is installed on the outer wall of the high-pressure reactor. Microwave-assisted heating is first used for 10 minutes to rapidly raise the temperature of the material to 110°C, and then the temperature is maintained at a normal level for 3.5 hours. After the reaction is completed, the cryolite is completely decomposed into sodium fluoride and sodium aluminate, resulting in an alkali-dissolved slurry.

[0037] Step S5: The alkaline slurry enters the crystallization unit. Sodium silicate is added to the crystallization unit as a silicon source, and the silicon-aluminum molar ratio in the mixture is adjusted to 2.0. At the same time, tetrapropylammonium hydroxide, a template agent, is added. The amount of template agent added is 0.3 times the molar amount of silicon dioxide in the silicon source. The crystallization unit is equipped with a segmented temperature controller. First, the temperature is controlled at 85℃ for crystallization for 3 hours, and then the temperature is increased to 110℃ for another 4 hours. After the crystallization reaction is completed, cooling water is introduced through the cooling coil inside the crystallization unit to rapidly cool the crystallization slurry to room temperature at a cooling rate of 10℃ / minute. Then, it is sent to the third filtration unit for solid-liquid separation to obtain molecular sieve products and crystallization mother liquor. After washing and drying, the molecular sieve products are detected by X-ray diffraction and have typical A-type or X-type molecular sieve crystal structures. The crystallization mother liquor is returned to the alkaline dissolution unit for recycling after sodium hydroxide is added.

[0038] In this embodiment, the lithium-precipitated liquid is sent to the evaporation and concentration unit for evaporation and concentration. Part of the concentrated liquid is returned to the acidolysis unit through the first reuse pipeline for the preparation of dilute sulfuric acid, and the other part is returned to the alkali dissolution unit through the second reuse pipeline for the preparation of sodium hydroxide solution, thereby realizing the recycling of water resources and residual acids and alkalis.

[0039] Through the gradual implementation of the above technical logic, this embodiment achieves efficient and selective extraction of lithium from aluminum electrolyte waste residue, while converting all components such as aluminum, fluorine, and silicon in the waste residue into molecular sieve products. The entire process involves no secondary waste discharge, meeting the requirements for the harmless treatment and resource utilization of hazardous waste.

[0040] Example 3 Taking the mixed waste residue of a certain electrolytic aluminum plant overhaul slag and waste electrolyte as an example, the waste residue contains 2.2% lithium by mass, 52% fluoride by mass, 22% aluminum by mass, and about 8% carbonaceous impurities by mass. The system of the present invention is used for processing, and the specific implementation process is as follows.

[0041] Step S1: The mixed waste residue is fed into the acidolysis unit. The crusher crushes the waste residue to less than 8 mm, and the grinder grinds it to a particle size of less than 200 mesh. The ground waste residue powder is fed into the acidolysis reactor with 12% (w / w) dilute sulfuric acid at a solid-liquid ratio of 1:5. The acidolysis reaction adopts a two-stage control method: the first stage is a reaction at 65℃ for 0.8 hours, and the second stage is a reaction at 85℃ for 1.2 hours. The stirring speed is maintained at 180 rpm. Ammonium sulfate is added to the dilute sulfuric acid at a concentration of 1.2% of the mass of the aluminum electrolyte waste residue, which effectively suppresses the escape of hydrogen fluoride gas. The acidolysis reaction is carried out in a closed reactor. The top of the reactor is connected to a hydrogen fluoride absorption device, which contains sodium hydroxide solution to ensure that the tail gas meets the emission standards. After the reaction is completed, the acidolysis slurry is obtained.

[0042] Step S2: The acid-hydrolyzed slurry enters the first pH adjustment unit, and calcium carbonate is added in batches to adjust the pH of the slurry to 3.8. At this time, aluminum ions and fluoride ions fully combine to form cryolite precipitate. Lithium ions are enriched in the liquid phase because they do not participate in the precipitation reaction. The first filtration unit filters the slurry to separate the lithium-containing filtrate and cryolite precipitate residue. A small amount of carbonaceous impurities carried in the cryolite precipitate residue are separated simultaneously in this step.

[0043] Step S3: The lithium-containing filtrate enters the lithium precipitation unit, where the temperature is controlled at 85°C. First, hydrogen peroxide is added at a volume of 0.4% of the lithium-containing filtrate to oxidize and decompose any trace organic matter that may remain in the filtrate. Then, sodium carbonate is added in two steps: after the first addition, the pH is adjusted to 7.3 and stirred for 0.5 hours; after the second addition, the pH is adjusted to 8.8 and the reaction continues for 1 hour. After the reaction is complete, the mixture is aged for 2.5 hours and then separated into solid and liquid components in the second filtration unit to obtain the lithium carbonate product and the lithium precipitation liquid. In this embodiment, the lithium extraction rate reaches 94%.

[0044] Step S4: The cryolite precipitate enters the alkali dissolution unit, which uses a high-pressure reactor with a reaction pressure set at 0.4 MPa. A 22% sodium hydroxide solution is added, with a solid-liquid ratio of 1:4. Sodium chloride is added to the reaction system at a rate of 12% of the mass of the cryolite precipitate. During the alkali dissolution reaction, argon gas is introduced from the bottom of the reactor at a flow rate of 1.5 liters / minute. Microwave-assisted heating is used with a microwave power of 600 watts. The material is heated to 115°C in 15 minutes, and then the temperature is maintained at a normal level for another 4 hours. After the reaction is completed, an alkali-dissolved slurry is obtained, with a cryolite decomposition rate exceeding 98%.

[0045] Step S5: The alkaline slurry enters the crystallization unit. Silica sol is added to the crystallization unit as a silicon source, and the silicon-aluminum molar ratio is adjusted to 2.2. At the same time, tetraethylammonium hydroxide, a template agent, is added. The amount of template agent added is 0.4 times the molar amount of silicon dioxide in the silicon source. Before the crystallization reaction, vinylidene fluoride is added to the mixture as a crystallization promoter, and the amount added is 0.15% of the mass of the mixture. The crystallization adopts a segmented heating method: the first stage is crystallization at 88℃ for 3.5 hours, and the second stage is heated to 115℃ for another 3.5 hours. After crystallization, it is rapidly cooled to room temperature at a cooling rate of 12℃ / min. Then, it undergoes solid-liquid separation in the third filtration unit to obtain molecular sieve products and crystallization mother liquor. After washing and drying, the molecular sieve products are tested and found to have a regular pore structure and a high specific surface area. The crystallization mother liquor is returned to the alkaline slurry unit for recycling after sodium hydroxide is added.

[0046] In this embodiment, the lithium-precipitated liquid enters the evaporation and concentration unit for evaporation and concentration. The concentrated liquid is then reused in the acidolysis unit and the alkali dissolution unit. The acidolysis unit is equipped with a stirrer and a heating jacket, and a hydrogen fluoride absorption tower at the top ensures the complete absorption of acidic gases. The alkali dissolution unit is equipped with a temperature controller and a pressure controller to ensure precise and stable reaction conditions. The segmented temperature rise controller and the internal cooling coil of the crystallization unit work together to achieve precise temperature control and rapid cooling in the crystallization process.

[0047] Through the step-by-step implementation of the above-mentioned technical means, this embodiment successfully extracted lithium from aluminum electrolyte mixed waste residue in the form of lithium carbonate, while converting aluminum, fluorine, and silicon components in the waste residue into high-value-added molecular sieve materials, realizing the full resource utilization and harmless disposal of hazardous waste.

[0048] 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.

Claims

1. A method for selectively extracting lithium from aluminum electrolyte waste and simultaneously preparing molecular sieves, characterized in that, Includes the following steps: S1. After crushing and grinding the aluminum electrolyte waste residue to a particle size of less than 200 mesh, mix it with dilute sulfuric acid with a mass concentration of 10%-20% at a solid-liquid ratio of 1:3-1:6, and stir and acidify at 60-90℃ for 1-3 hours to obtain acid slurry. S2. Add calcium carbonate to the acid hydrolysis slurry in batches to adjust the pH of the slurry to 3.0-4.0, so that aluminum ions and fluoride ions co-precipitate into cryolite, while lithium ions remain in the liquid phase. After filtration, separate the lithium-containing filtrate and cryolite precipitate residue. S3. Add sodium carbonate to the lithium-containing filtrate, adjust the pH to 8.0-9.0, precipitate lithium ions at 70-90℃ to obtain lithium carbonate, and obtain lithium carbonate product after solid-liquid separation. The remaining liquid is the lithium precipitation liquid. S4. Mix cryolite precipitate residue with sodium hydroxide solution of 10%-25% by mass at a solid-liquid ratio of 1:2-1:5, and react with alkaline solution at 90-120℃ for 2-5 hours to convert cryolite into sodium fluoride and sodium aluminate to obtain alkaline slurry. S5. Add silicon source to alkaline slurry, adjust silicon-aluminum molar ratio to 1.5-2.5, crystallize at 80-120℃ for 4-10 hours, and obtain molecular sieve product after solid-liquid separation, washing and drying.

2. The method according to claim 1, characterized in that, In step S1, the solid-liquid ratio of aluminum electrolyte waste residue to dilute sulfuric acid is 1:3-1:6, the mass concentration of dilute sulfuric acid is 10%-20%, the acidolysis reaction temperature is 60-90℃, and the reaction time is 1-3 hours. Furthermore, at least one of the following control methods is executed in step S1: Method 1: During the acid hydrolysis reaction, the stirring speed is 150-300 rpm. Method 2: The acid hydrolysis reaction is carried out in two stages. The first stage is carried out at 60-70℃ for 0.5-1 hour, and the second stage is carried out at 80-90℃ for 0.5-2 hours. Method 3: Add ammonium sulfate to dilute sulfuric acid. The amount of ammonium sulfate added is 0.5%-2% of the mass of aluminum electrolyte waste residue, which is used to suppress the escape of hydrogen fluoride gas. Method 4: The acidolysis reaction is carried out in a closed reactor and connected to a hydrogen fluoride absorption device, which contains a sodium hydroxide solution.

3. The method according to claim 1, characterized in that, In step S3, the lithium precipitation liquid is evaporated and concentrated and then returned to step S1 to prepare dilute sulfuric acid, or returned to step S4 to prepare sodium hydroxide solution. Furthermore, at least one of the following operations is performed in step S3: Operation 1: Before adding sodium carbonate, add hydrogen peroxide to the lithium-containing filtrate. The amount of hydrogen peroxide added is 0.1%-0.5% of the volume of the lithium-containing filtrate, which is used to oxidize and remove organic impurities. Operation 2: While adding sodium carbonate, lithium carbonate seed crystals are added simultaneously. The amount of seed crystals added is 0.5%-2% of the expected lithium carbonate yield, and the seed crystal particle size is 5-20 micrometers. Operation 3: The lithium carbonate precipitation reaction is carried out by adding sodium carbonate in two stages. The first time, sodium carbonate is added to adjust the pH value to 7.0-7.5, and the reaction is stirred for 0.5 hours. The second time, sodium carbonate is added to adjust the pH value to 8.0-9.0, and the reaction is continued for 1 hour. Operation 4: The lithium precipitation reaction temperature is 70-90℃. After the reaction is completed, age at room temperature for 1-3 hours before solid-liquid separation.

4. The method according to claim 1, characterized in that, In step S4, the mass concentration of sodium hydroxide solution is 10%-25%, the solid-liquid ratio of cryolite precipitate to sodium hydroxide solution is 1:2-1:5, the alkaline dissolution reaction temperature is 90-120℃, and the reaction time is 2-5 hours. Furthermore, at least one of the following reinforcement measures is performed in step S4: Enhancement measure 1: The alkaline dissolution reaction is carried out in a high-pressure reactor at a pressure of 0.2-0.5 MPa; Enhancement measure 2: Add sodium chloride to the alkaline dissolution reaction system. The amount of sodium chloride added is 5%-15% of the mass of the cryolite precipitate, which is used to promote the exchange and dissociation of sodium ions in the cryolite. Enhancement measure three: During the alkaline dissolution reaction, a protective gas is introduced. The protective gas is nitrogen or argon, and the gas flow rate is 0.5-2 liters / minute to prevent interference from carbon dioxide in the air. Enhancement Measure 4: The alkali dissolution reaction adopts microwave-assisted heating with a microwave power of 300-800 watts and a heating time of 10-30 minutes, so that the cryolite precipitate is rapidly heated to the reaction temperature and then switched to conventional heat preservation.

5. The method according to claim 1, characterized in that, In step S5, the silicon source is sodium silicate or silica sol. The mother liquor obtained after solid-liquid separation after crystallization is returned to step S4 for recycling after sodium hydroxide is added. Furthermore, at least one of the following control measures is performed in step S5: Control method 1: When adding a silicon source to the alkaline slurry, add a template agent, which is tetrapropylammonium hydroxide or tetraethylammonium hydroxide. The amount of template agent added is 0.1-0.5 times the molar amount of silicon dioxide in the silicon source. Control method two: The crystallization reaction adopts a segmented heating method. The first stage is crystallization at 80-90℃ for 2-4 hours, and the second stage is heated to 100-120℃ to continue crystallization for 2-6 hours. Control method three: Before the crystallization reaction, add a crystallization accelerator to the mixture of alkaline solution and silicon source. The crystallization accelerator is vinylidene fluoride or polyethylene glycol, and the amount added is 0.05%-0.2% of the mass of the mixture. Control method four: After the crystallization reaction is completed, the crystallization slurry is rapidly cooled to room temperature at a rate of 5-15℃ / minute, and then solid-liquid separation is performed.

6. A system for selectively extracting lithium from aluminum electrolyte waste and simultaneously preparing molecular sieves to implement the method described in any one of claims 1-5, characterized in that, include: The acidolysis unit is used to crush and grind aluminum electrolyte waste residue and mix it with dilute sulfuric acid to carry out an acidolysis reaction to obtain an acidolysis slurry. The first pH adjustment unit is connected to the outlet of the acid hydrolysis unit. It is used to add calcium carbonate to the acid hydrolysis slurry and adjust the pH value to 3.0-4.0, so that aluminum ions and fluoride ions precipitate in the form of cryolite, while lithium ions remain in the solution. The first filtration unit is connected to the outlet of the first pH adjustment unit and filters the slurry output by the first pH adjustment unit to obtain lithium-containing filtrate and cryolite precipitate. The lithium precipitation unit is connected to the lithium-containing filtrate outlet of the first filtration unit. It is used to add sodium carbonate to the lithium-containing filtrate and adjust the pH value to 8.0-9.0, so that lithium ions precipitate in the form of lithium carbonate. The second filtration unit is connected to the outlet of the lithium precipitation unit and performs solid-liquid separation on the slurry output from the lithium precipitation unit to obtain lithium carbonate product and lithium precipitation liquid. The alkali dissolution unit is connected to the cryolite precipitate outlet of the first filtration unit. It is used to mix the cryolite precipitate with sodium hydroxide solution and carry out an alkali dissolution reaction under heating conditions, so that the cryolite decomposes to generate sodium fluoride and sodium aluminate, and obtains alkali dissolution slurry. The crystallization unit, connected to the outlet of the alkali dissolution unit, is used to add a silicon source to the alkali dissolution slurry, adjust the silicon-aluminum molar ratio to 1.5-2.5, and crystallize at 80-120℃ for 4-10 hours to obtain a crystallized slurry. The third filtration unit is connected to the outlet of the crystallization unit to perform solid-liquid separation on the crystallization slurry, obtaining molecular sieve products and crystallization mother liquor.

7. The system according to claim 6, characterized in that, The system also includes: An evaporation and concentration unit is connected to the lithium precipitation liquid outlet of the second filtration unit and is used to evaporate and concentrate the lithium precipitation liquid. The first pipeline connects the concentrated liquid outlet of the evaporation and concentration unit to the dilute sulfuric acid inlet of the acidolysis unit, and is used to return the concentrated liquid to the acidolysis unit to prepare dilute sulfuric acid. The second pipeline connects the concentrated liquid outlet of the evaporation and concentration unit to the sodium hydroxide solution inlet of the alkali dissolution unit, and is used to return the concentrated liquid to the alkali dissolution unit to prepare sodium hydroxide solution. The acid hydrolysis unit is equipped with a stirrer, and the stirrer speed is controlled within the range of 150-300 rpm. The acid hydrolysis unit is equipped with a heating jacket, and hot water or steam is circulated inside the heating jacket; The top of the acidolysis unit is connected to a hydrogen fluoride absorption tower, which is filled with sodium hydroxide solution.

8. The system according to claim 6, characterized in that, The alkali dissolution unit includes a heating jacket and a temperature controller. The heating jacket is fitted onto the outer wall of the reaction vessel of the alkali dissolution unit, and the temperature controller is connected to the heating jacket to control the alkali dissolution reaction temperature at 90-120℃. The alkali dissolution unit is a high-pressure reactor, which is equipped with a pressure controller with a pressure control range of 0.2-0.5 MPa. The high-pressure reactor is equipped with an agitator, which adopts an anchor or paddle structure. A microwave generator is installed on the outer wall or inside the high-pressure reactor, with a power of 300-800 watts.

9. The system according to claim 6, characterized in that, The system also includes: The mother liquor recycling pipeline connects the crystallization mother liquor outlet of the third filtration unit and the inlet of the alkali dissolution unit, and is used to return the crystallization mother liquor to the alkali dissolution unit for recycling after adding sodium hydroxide; The crystallization unit is equipped with a segmented temperature controller, which is used to control the crystallization unit to be kept at 80-90℃ for 2-4 hours and at 100-120℃ for 2-6 hours in sequence. The crystallization unit is equipped with a cooling coil, which is circulated with cooling water at a cooling rate of 5-15℃ / minute.

10. The system according to claim 6, characterized in that, The acid hydrolysis unit includes a crusher, a grinder, and an acid hydrolysis reactor connected in sequence. The discharge port of the crusher is connected to the inlet of the grinder, and the discharge port of the grinder is connected to the solid feed inlet of the acid hydrolysis reactor. The acid hydrolysis reactor is equipped with a dilute sulfuric acid inlet, a stirrer, and a heating jacket. The lithium deposition unit includes a sodium carbonate storage tank, a hydrogen peroxide storage tank, and a seed crystal feeder. The sodium carbonate storage tank is connected to the reaction vessel of the lithium deposition unit via a metering pump. The hydrogen peroxide storage tank is connected to the reaction vessel of the lithium deposition unit via a pipeline. The outlet of the seed crystal feeder extends into the reaction vessel of the lithium deposition unit. The outlet of the second filtration unit is connected to the inlet of the evaporation and concentration unit, which is equipped with a condensate outlet and a concentrate outlet.

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