Method for comprehensively recovering waste electrolyte containing lithium and aluminum

Abstract

The invention provides a method for comprehensively recovering a waste electrolyte containing lithium and aluminum. The method comprises the following steps: carrying out alkaline leaching treatment on the waste lithium-containing aluminum electrolyte, and carrying out solid-liquid separation to obtain a first filtrate and a first filter residue; carrying out water washing treatment on the first filter residue, and carrying out solid-liquid separation to obtain a second filtrate and a second filter residue; mixing the first filtrate and the second filtrate, and introducing carbon dioxide for reaction to obtain cryolite and third filtrate; sequentially carrying out acid leaching treatment and two-stage impurity removal treatment on the second filter residue to obtain fourth filtrate; and finally, carrying out lithium precipitation treatment on the fourth filtrate to obtain lithium carbonate. According to the method, the fluorine element and the aluminum element can be recycled while the lithium element in the waste lithium-containing aluminum electrolyte is recycled at high efficiency and low cost, the lithium element recycling rate is 95% or above, the fluorine element recycling rate is 75% or above, and the solid waste amount in the recycling process is reduced by 65% or above.

Description

Technical Field

[0001] The invention belongs to the technical field of industrial solid waste recycling, and specifically relates to a method for comprehensive recycling of waste lithium-aluminum-containing electrolytes. Background Art

[0002] The electrolytic aluminum industry produces a large amount of waste electrolyte, the main component of which is cryolite (Na 3 AlF 6 ), and also contains a small amount of calcium fluoride, lithium fluoride, potassium fluoride, magnesium fluoride and aluminum oxide. In particular, the content of lithium in the electrolyte can reach 1-3%, which is equivalent to Li 2 The content of O is 2.1-6.4%, which is close to the 1.5-7% of lithium in spodumene ore, providing the possibility of recycling lithium resources. Therefore, recycling these elements can not only create higher economic value, but also reduce solid waste emissions and promote the green development of the electrolytic aluminum industry.

[0003] Based on this, many technical solutions have been disclosed in the prior art. For example, patent CN117965891A discloses a method for extracting lithium from aluminum electrolyte waste slag. This method fixes the aluminum element in the raw material by adding calcium-containing compounds, which makes it impossible to further recover the aluminum element and greatly increases the slag production, creating great pressure on subsequent processing.

[0004] Patent CN105543504A proposes to mix aluminum electrolyte and sodium fluoride and roast them at high temperature to convert the insoluble lithium salt in the electrolyte into soluble lithium fluoride, and then add acid to leach and recover the lithium element. Although this method can effectively extract the lithium element in the aluminum electrolyte, the fluorination roasting process will cause great corrosion to the industrial kiln, making it difficult to operate stably.

[0005] Patent CN113684369A discloses that the waste industrial lithium-aluminum electrolyte to be treated is mixed with alkali and roasted to convert the lithium-sodium composite cryolite in the lithium-aluminum electrolyte into LiAl 2 (OH) 7 , and then the lithium element is separated by water leaching and acid leaching, and part of the fluorine element and aluminum element are recovered and regenerated into cryolite and hydroxyaluminum fluoride products, and finally the waste liquid is evaporated and crystallized to obtain metal salt. Although this method recovers lithium and other valuable elements, the purity of the regenerated hydroxyaluminum fluoride product cannot be guaranteed, and it has a low economic value. In addition, the evaporation and crystallization treatment method will also generate huge energy consumption, making the preparation process of the metal salt have a high cost.

[0006] Therefore, in this field, there is an urgent need to develop a method for efficiently and comprehensively recovering different elements in waste electrolytes to solve the above problems. Summary of the invention

[0007] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for comprehensive recovery of waste lithium-aluminum electrolytes. The present invention can recover the lithium element in the waste lithium-aluminum electrolytes efficiently and at low cost while recovering the fluorine element and the aluminum element through a hydrometallurgical process, thereby achieving a lithium recovery rate of more than 95% and a fluorine recovery rate of more than 75%, and the amount of solid waste is reduced by more than 65% during the recovery process, which has obvious economic and environmental benefits.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for comprehensive recovery of waste lithium-aluminum electrolyte, the method comprising the following steps:

[0010] S1. The waste lithium-aluminum electrolyte is subjected to alkaline leaching treatment, and a first filtrate and a first filter residue are obtained after solid-liquid separation;

[0011] S2. washing the first filter residue with water, and obtaining a second filtrate and a second filter residue after solid-liquid separation;

[0012] S3. The first filtrate and the second filtrate are mixed, carbon dioxide is introduced to react, and cryolite and a third filtrate are obtained after solid-liquid separation;

[0013] S4. The second filter residue is sequentially subjected to acid leaching treatment and two-stage impurity removal treatment to obtain a fourth filtrate;

[0014] S5. The fourth filtrate is subjected to lithium precipitation treatment to obtain lithium carbonate.

[0015] The present invention aims at the following problems existing in the existing waste lithium-aluminum electrolyte recovery process: (1) the existence form of lithium in the raw material is complex, the cost of the existing extraction process is high, and the yield of lithium is low; (2) the recovery technical means are single in form, most of which can only recover the lithium in the raw material, and cannot recover other valuable elements by low-cost and high-efficiency technical means, so that the economic benefits are not obvious; (3) the total amount of solid waste generated in the recovery process cannot be further reduced, and the generated high-salt wastewater is difficult to treat, so it faces great environmental pressure. The present invention uses the waste lithium-aluminum electrolyte generated in the electrolytic aluminum industrial production process as raw material, takes the extraction of lithium as the starting point, adopts a specific hydrometallurgical process, firstly uses alkaline leaching treatment and water washing treatment to separate lithium, fluorine and aluminum at the same time; secondly, introduces carbon dioxide to react and prepares cryolite, thereby recovering fluorine and aluminum; finally, lithium carbonate is prepared by acid leaching treatment, two-stage impurity removal treatment and lithium precipitation treatment, thereby recovering lithium. Therefore, the method for comprehensive recovery of waste lithium-aluminum electrolytes provided by the present invention can achieve a lithium element recovery rate of more than 95% and a fluorine element recovery rate of more than 75%, and the amount of solid waste is reduced by more than 65% during the recovery process, which has obvious economic and environmental benefits.

[0016] In addition, the sodium-containing high-salt wastewater generated in the recovery process of the present invention can be subsequently prepared into acid solution and alkali solution through bipolar membrane electrodialysis technology for recycling, which greatly reduces the wastewater discharge and production costs.

[0017] Preferably, the alkali leaching process in step S1 includes mixing the waste lithium-aluminum-containing electrolyte and alkali solution, so that the cryolite in the waste lithium-aluminum-containing electrolyte can be decomposed in the alkali solution to generate sodium aluminate and sodium fluoride, and after solid-liquid separation, a first filtrate (sodium aluminate solution) and a first filter residue (containing lithium precipitate and sodium fluoride) are obtained.

[0018] In the present invention, the alkali solution exemplarily includes sodium hydroxide solution.

[0019] Preferably, the liquid-to-solid mass ratio of the alkali solution to the waste lithium-aluminum-containing electrolyte is (1-7):1, preferably (3-5):1, for example, it can be 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, 2.2:1, 2.5:1, 2.8:1, 3:1, 3.2:1, 3.5:1, 3.8:1, 4:1, 4.2:1, 4.5:1, 4.8:1, 5:1, 5.2:1, 5.5:1, 5.8:1, 6:1, 6.2:1, 6.5:1, 6.8:1, 7:1, etc.

[0020] Preferably, the mass of the solute in the alkali solution satisfies the relationship: m 2 =k×(3+1.82×m 1), where m 2 is the mass of the solute in the alkali solution, k is in the range of 0.3 to 0.8, preferably 0.5 to 0.7, m 1 It is the mass of fluorine element in the discarded lithium-aluminum electrolyte.

[0021] In the present invention, the value range of k is 0.3 to 0.8, for example, it can be 0.3, 0.32, 0.35, 0.38, 0.4, 0.42, 0.45, 0.48, 0.5, 0.52, 0.55, 0.58, 0.6, 0.62, 0.65, 0.68, 0.7, 0.72, 0.75, 0.78, 0.8, etc. The present invention regulates the value range of k to a suitable range, so that the cryolite in the waste lithium-aluminum electrolyte can be completely converted into sodium aluminate and sodium fluoride, while the lithium-containing cryolite ((Na, K, Ca) n Li 3-n AlF 6 ) is converted to LiAl 2 (OH) 7 If a smaller k value is used, the above process will not be completely transformed; if a larger k value is used, LiAl 2 (OH) 7 Further dissolution causes Li to enter the liquid phase and become difficult to recover.

[0022] Preferably, the temperature of the alkali leaching treatment in step S1 is 50°C to 100°C, for example, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, etc.

[0023] Preferably, the pressure of the alkali leaching treatment in step S1 is normal pressure.

[0024] Preferably, the alkali leaching treatment time in step S1 is 2 h to 8 h, for example, it can be 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, etc.

[0025] Preferably, the mass ratio of water to the waste lithium-aluminum electrolyte during the water washing treatment in step S2 is (20-40):1, preferably (25-35):1, for example, 20:1, 22:1, 25:1, 28:1, 30:1, 32:1, 35:1, 38:1, 40:1, etc. In the present invention, a large amount of sodium fluoride in the first filter residue is dissolved by water washing treatment, thereby obtaining a sodium fluoride solution and a lithium-containing filter residue.

[0026] Preferably, the reaction temperature in step S3 is 25°C to 30°C, for example, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, etc.

[0027] Preferably, the pH value of the system after the reaction in step S3 is 6 to 10, for example, it can be 6, 7, 7.2, 7.5, 7.8, 8, 8.2, 8.5, 8.8, 9, 9.2, 9.5, 9.8, 10, etc.

[0028] Preferably, the third filtrate in step S3 is returned to step S2 for recycling.

[0029] In the present invention, in step S3, sufficient amount of carbon dioxide is introduced into the first filtrate (sodium aluminate solution) and the second filtrate (sodium fluoride solution) to generate cryolite crystal precipitation.

[0030] In the present invention, carbon dioxide (CO 2 ) Adjusting the pH value of the reaction in step S3 can avoid the introduction of additional other types of anions or organic acid ions, which in turn affects the purity of the regenerated cryolite product, and reduce the amount of sodium fluoride dissolved during the recycling process of returning to step S2. Therefore, carbon dioxide is preferably used for treatment.

[0031] Preferably, the acid leaching process in step S4 includes slurrying the second filter residue to obtain slurry; and then subjecting the slurry to an acidification reaction with an acid solution.

[0032] In the present invention, the acid solution exemplarily includes sulfuric acid and / or hydrochloric acid.

[0033] Preferably, the slurry treatment process includes mixing the second filter residue and water into slurry.

[0034] Preferably, the liquid-solid mass ratio of the water to the second filter residue is (0.35-5):1, for example, it can be 0.35, 0.4, 0.45, 0.5:1, 0.8:1, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, 2.2:1, 2.5:1, 2.8:1, 3:1, 3.2:1, 3.5:1, 3.8:1, 4:1, 4.2:1, 4.5:1, 4.8:1, 5:1, etc.

[0035] Preferably, the temperature of the acidification reaction is 25°C to 100°C, for example, 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, etc.

[0036] Preferably, the pressure of the acidification reaction is normal pressure.

[0037] Preferably, the pH value of the system after the acidification reaction is ≤4.0, preferably 0.5-4, for example, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, etc. The present invention reduces the corrosion to the equipment by regulating the pH value of the system in the acidification reaction.

[0038] In the present invention, the second filter residue is first subjected to slurry treatment to obtain slurry; and then the slurry and acid solution are subjected to acidification reaction again, so that the process wastewater generated is more suitable for acid-base regeneration treatment using bipolar membrane electrodialysis technology.

[0039] In the present invention, after the acidification reaction is completed, a lithium-containing leaching solution and a first external slag (mainly composed of fluorine, aluminum and calcium) are obtained.

[0040] Preferably, the two-stage impurity removal treatment in step S4 includes a first stage impurity removal treatment and a second stage impurity removal treatment in sequence, so as to obtain a purified lithium-containing liquid.

[0041] Preferably, the first stage of impurity removal treatment comprises a first stirring reaction of the lithium-containing leaching solution obtained after the acid leaching treatment with an alkaline solution, and obtaining a filtrate A and a filter residue A after solid-liquid separation.

[0042] In the present invention, the components of the filter residue A are mainly hydroxyaluminum fluoride and aluminum hydroxide, which will cause co-precipitation and adsorption of lithium ions during the generation process, resulting in obvious lithium loss. By returning the filter residue A to step S1 for further reaction, the lithium element, aluminum element and fluorine element are returned to the main process and recovered again, thereby greatly improving the comprehensive recovery efficiency of each element.

[0043] Preferably, the temperature of the first stirring reaction is 25°C to 100°C, for example, 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, etc.

[0044] Preferably, the pressure of the first stirring reaction is normal pressure.

[0045] Preferably, after the first stirring reaction, the pH value of the system is 6-7, for example, 6, 6.2, 6.5, 6.8, 7, etc.

[0046] Preferably, the second stage of impurity removal treatment comprises subjecting the filtrate A and the alkali solution to a second stirring reaction, and obtaining a fourth filtrate after solid-liquid separation.

[0047] In the present invention, the fourth filtrate and the second external slag (mainly composed of calcium and magnesium) are obtained after solid-liquid separation.

[0048] Preferably, the temperature of the second stirring reaction is 25°C to 100°C, for example, 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, etc.

[0049] Preferably, the pressure of the second stirring reaction is normal pressure.

[0050] Preferably, the pH value of the second stirring reaction is 10-11, for example, 10, 10.2, 10.5, 10.8, 11, etc.

[0051] Preferably, the lithium precipitation treatment process in step S5 includes adding a lithium precipitation agent.

[0052] Preferably, the lithium precipitating agent comprises sodium carbonate.

[0053] Preferably, after the lithium precipitation treatment in step S5 is completed, the precipitation mother liquor is further subjected to acid-base regeneration treatment to obtain acid solution and alkali solution.

[0054] In the present invention, the acid-base regeneration treatment can regenerate the sodium salt (sodium sulfate / sodium chloride) in the process wastewater to obtain sulfuric acid / hydrochloric acid and sodium hydroxide, which are returned to the production line as raw materials, reflecting obvious economic benefits.

[0055] Preferably, the acid-base regeneration treatment method includes bipolar membrane electrodialysis.

[0056] Preferably, the acid solution is returned to step S4 for recycling.

[0057] Preferably, the alkali solution is returned to step S1 and / or step S4 for recycling.

[0058] It should be noted that the various filter residues described in the above steps of the present invention, unless otherwise specified, are all wet residues (not dried).

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] The present invention provides a method for comprehensive recovery of discarded lithium-aluminum electrolytes. The present invention uses the discarded lithium-aluminum electrolytes generated in the production process of electrolytic aluminum industry as raw materials, takes the extraction of lithium element as the starting point, and adopts a specific hydrometallurgical process. First, the lithium element, the fluorine element and the aluminum element are separated simultaneously by alkaline leaching treatment and water washing treatment in sequence; secondly, carbon dioxide is introduced for reaction to prepare cryolite, thereby recovering the fluorine element and the aluminum element; finally, lithium carbonate is prepared by acid leaching treatment, two-stage impurity removal treatment and lithium precipitation treatment in sequence, thereby recovering the lithium element. Therefore, the method for comprehensive recovery of discarded lithium-aluminum electrolytes provided by the present invention can achieve a lithium element recovery rate of more than 95% and a fluorine element recovery rate of more than 75%, and the amount of solid waste is reduced by more than 65% during the recovery process, which has obvious economic and environmental benefits.

[0061] In addition, the sodium-containing high-salt wastewater generated in the recovery process of the present invention can be subsequently prepared into acid solution and alkali solution through bipolar membrane electrodialysis technology for recycling, thereby achieving the co-production of products such as lithium carbonate and cryolite, greatly reducing wastewater discharge and production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 A flow chart of the method for comprehensive recovery of waste lithium-aluminum-containing electrolytes provided by the present invention. DETAILED DESCRIPTION

[0063] The technical solution of the present invention is further described below by combining the accompanying drawings and specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0064] In the embodiments and comparative examples provided by the present invention, the chemical composition (by mass percentage) of the waste lithium-aluminum electrolyte is as follows: Li 2 O 3.2%, F 52.8%, Al 2 O 3 18.3%, Na 2 O 20.9%, K 2 O 1.27%, CaO 2.64%, MgO 0.31%, and others 0.58%.

[0065] Example 1

[0066] This embodiment provides a method for comprehensive recovery of waste lithium-aluminum electrolytes, such as Figure 1 As shown, the method comprises the following steps:

[0067] S1. 1 kg of waste lithium-aluminum electrolyte powder was mixed with 600 g of solid sodium hydroxide and 4 L of water for alkaline leaching, the temperature was raised to 85 ° C, and the reaction was stirred at normal pressure for 3 h, and then filtered to obtain 3.3 L of the first filtrate and 2.3 kg of the first filter residue;

[0068] S2. The first residue was mixed with 30 L of water and stirred, washed with water, and after solid-liquid separation, 30.8 L of the second filtrate and 1.5 kg of the second residue were obtained;

[0069] S3. The first filtrate and the second filtrate are mixed and stirred, and carbon dioxide (CO 2 ) to react until the pH value of the system is 8 after the reaction is completed, and filtered to separate to obtain 747 g of cryolite (after drying) and 33.2 L of the third filtrate, and the third filtrate is returned to step S2 for recycling;

[0070] S4. 1.5 kg of the second filter residue and 1.5 L of water were mixed and slurried to obtain a slurry; the temperature was raised to 85 ° C, and 3.4 mol of H was added to the slurry under normal pressure. 2 SO 4The acidification reaction was carried out for 2 hours. After the acidification reaction, the pH value of the system was 3.6. The solution was filtered and separated to obtain 1.87 L of lithium-containing leaching solution and 345 g of the first external slag (water content 23%).

[0071] The lithium-containing leachate was heated to 60° C., 450 mL of a 1 mol / L sodium hydroxide solution was slowly added under normal pressure until the pH value of the reaction end point was 6, the mixture was stirred for reaction, and the first stage of impurity removal treatment was performed. 1.6 L of filtrate A and 1.2 kg of filter residue A were obtained by filtration and separation, and the filter residue A was returned to step S1;

[0072] The filtrate A was heated to 40°C, 75 mL of a 1 mol / L sodium hydroxide solution was slowly added under normal pressure until the pH value of the reaction reached 11 at the end point, the mixture was stirred for reaction, and the second stage of impurity removal was performed. 1.6 L of the fourth filtrate (with a lithium ion concentration of 1.29 mol / L) and 64 g of the second external slag (with a water content of 42%) were obtained by filtration and separation;

[0073] S5. The fourth filtrate was concentrated and then added with sufficient sodium carbonate to precipitate lithium to obtain an industrial grade lithium carbonate product 75.9g and a precipitated mother liquor;

[0074] S6. The precipitated mother liquor is subjected to acid-base regeneration treatment by bipolar membrane electrodialysis technology to obtain a regenerated sulfuric acid solution (H 2 SO 4 The mass of the reaction mixture is 282 g) and regenerated sodium hydroxide solution (the mass of NaOH is 230 g), wherein the sulfuric acid solution is returned to step S4, and the sodium hydroxide solution is returned to steps S1 and S4.

[0075] Calculations show that the recovery rate of lithium in this embodiment is 95.9%, and the recovery rate of fluorine is 76.8%.

[0076] Example 2

[0077] This embodiment provides a method for comprehensive recovery of waste lithium-aluminum electrolyte, the method comprising the following steps:

[0078] S1. 1 kg of waste lithium-aluminum electrolyte powder was mixed with 500 g of solid sodium hydroxide and 3 L of water for alkaline leaching, the temperature was raised to 85 ° C, and the reaction was stirred at normal pressure for 3 h, and then filtered to obtain 2.1 L of the first filtrate and 2.4 kg of the first filter residue;

[0079] S2. The first residue was mixed with 25L of water and stirred, washed with water, and after solid-liquid separation, 25.5L of the second filtrate and 1.5kg of the second residue were obtained;

[0080] S3. The first filtrate and the second filtrate were mixed and stirred, and CO was introduced at room temperature. 2The reaction was continued until the pH value of the system was 10 after the reaction was completed, and 732 g of cryolite (after drying) and 26.7 L of the third filtrate were obtained, and the third filtrate was returned to step S2 for recycling;

[0081] S4. 1.5 kg of the second filter residue and 1.5 L of water were mixed and slurried to obtain a slurry; the temperature was raised to 85 ° C, and 3.4 mol of H was added to the slurry under normal pressure. 2 SO 4 The acidification reaction was carried out for 2 hours. After the acidification reaction, the pH value of the system was 3.6. The solution was filtered and separated to obtain 1.87 L of lithium-containing leaching solution and 355 g of the first external slag (water content 23%).

[0082] The lithium-containing leachate was heated to 60° C., 450 mL of a 1 mol / L sodium hydroxide solution was slowly added under normal pressure until the pH value of the reaction end point was 6, the mixture was stirred for reaction, and the first stage of impurity removal treatment was performed. 1.6 L of filtrate A and 1.2 kg of filter residue A were obtained by filtration and separation, and the filter residue A was returned to step S1;

[0083] The filtrate A was heated to 40°C, 75 mL of a 1 mol / L sodium hydroxide solution was slowly added under normal pressure until the pH value of the reaction reached 11 at the end point, the mixture was stirred for reaction, and the second stage of impurity removal was performed. 1.6 L of the fourth filtrate (with a lithium ion concentration of 1.28 mol / L) and 64 g of the second external slag (with a water content of 42%) were obtained by filtration and separation;

[0084] S5. The fourth filtrate was concentrated and then added with sufficient sodium carbonate to precipitate lithium to obtain an industrial grade lithium carbonate product 75.4g and a precipitated mother liquor;

[0085] S6. The precipitated mother liquor is subjected to acid-base regeneration treatment by bipolar membrane electrodialysis technology to obtain a regenerated sulfuric acid solution (H 2 SO 4 The mass of the sulfuric acid solution is 280g) and the mass of the sodium hydroxide solution is regenerated (the mass of NaOH is 228g), wherein the sulfuric acid solution is returned to step S4, and the sodium hydroxide solution is returned to steps S1 and S4.

[0086] Calculations show that the recovery rate of lithium in this embodiment is 95.2%, and the recovery rate of fluorine is 75.3%.

[0087] Example 3

[0088] This embodiment provides a method for comprehensive recovery of waste lithium-aluminum electrolyte, the method comprising the following steps:

[0089] S1. 1 kg of waste lithium-aluminum electrolyte powder was mixed with 700 g of solid sodium hydroxide and 5 L of water for alkaline leaching, the temperature was raised to 85 ° C, and the reaction was stirred at normal pressure for 3 h, and then filtered to obtain 4.5 L of the first filtrate and 2.2 kg of the first filter residue;

[0090] S2. The first filter residue was mixed with 35L of water and stirred, washed with water, and after solid-liquid separation, 35.3L of the second filtrate and 1.4kg of the second filter residue were obtained;

[0091] S3. The first filtrate and the second filtrate were mixed and stirred, and CO was introduced at room temperature. 2 The reaction was continued until the pH value of the system was 6 after the reaction was completed, and 740.9 g of cryolite (after drying) and 39.3 L of the third filtrate were obtained, and the third filtrate was returned to step S2 for recycling;

[0092] S4. 1.4 kg of the second filter residue and 1.5 L of water were mixed and slurried to obtain a slurry; the temperature was raised to 85 ° C, and 3.4 mol of H was added to the slurry under normal pressure. 2 SO 4 The acidification reaction was carried out for 2 hours. After the acidification reaction, the pH value of the system was 3.6. The solution was filtered and separated to obtain 1.85 L of lithium-containing leaching solution and 335 g of the first external slag (water content 23%).

[0093] The lithium-containing leachate was heated to 60° C., 450 mL of a 1 mol / L sodium hydroxide solution was slowly added under normal pressure until the pH value of the reaction end point was 6, the mixture was stirred for reaction, and the first stage of impurity removal treatment was performed. 1.6 L of filtrate A and 1.2 kg of filter residue A were obtained by filtration and separation, and the filter residue A was returned to step S1;

[0094] The filtrate A was heated to 40°C, 75 mL of a 1 mol / L sodium hydroxide solution was slowly added under normal pressure until the pH value of the reaction end point was 11, the reaction was stirred, and the second stage of impurity removal was performed, and 1.6 L of the fourth filtrate (the concentration of lithium ions was 1.283 mol / L) and 64 g of the second external slag (water content 42%) were obtained by filtration and separation;

[0095] S5. The fourth filtrate was concentrated and then added with sufficient sodium carbonate to precipitate lithium to obtain an industrial grade lithium carbonate product 75.5g and a precipitated mother liquor;

[0096] S6. The precipitated mother liquor is subjected to acid-base regeneration treatment by bipolar membrane electrodialysis technology to obtain a regenerated sulfuric acid solution (H 2 SO 4 The mass of the reaction mixture is 281 g) and regenerated sodium hydroxide solution (the mass of NaOH is 229 g), wherein the sulfuric acid solution is returned to step S4, and the sodium hydroxide solution is returned to steps S1 and S4.

[0097] Calculations show that the recovery rate of lithium in this embodiment is 95.4%, and the recovery rate of fluorine is 76.2%.

[0098] Example 4

[0099] This embodiment provides a method for comprehensive recovery of waste lithium-aluminum electrolyte, the method comprising the following steps:

[0100] S1. 1 kg of waste lithium-aluminum electrolyte powder was mixed with 386 g of solid sodium hydroxide and 2 L of water for alkaline leaching, the temperature was raised to 50 ° C, and the reaction was stirred at normal pressure for 8 hours, and then filtered to obtain 1.206 L of the first filtrate and 2.18 kg of the first filter residue;

[0101] S2. The first residue was mixed with 25 L of water and washed with water, and after solid-liquid separation, 25.2 L of the second filtrate and 1.42 kg of the second residue were obtained;

[0102] S3. The first filtrate and the second filtrate were mixed and stirred, and CO was introduced at room temperature. 2 The reaction was continued until the pH value of the system was 6 after the reaction was completed, and 478.4 g of cryolite (after drying) and 25.6 L of the third filtrate were obtained, and the third filtrate was returned to step S2 for recycling;

[0103] S4. 1.42 kg of the second filter residue and 0.5 L of water were mixed and slurried to obtain a slurry; the temperature was raised to 50 ° C, and 3.7 mol of H was added to the slurry under normal pressure. 2 SO 4 The acidification reaction was carried out for 2 hours. After the acidification reaction was completed, the pH value of the system was 3. The solution was filtered and separated to obtain 1.4 L of lithium-containing leaching solution and 499 g of the first external slag (water content 21%).

[0104] The lithium-containing leachate was heated to 35° C., 450 mL of a 1 mol / L sodium hydroxide solution was slowly added under normal pressure until the pH value of the reaction end point was 6, the mixture was stirred for reaction, and the first stage of impurity removal treatment was performed. 1.2 L of filtrate A and 770 g of filter residue A were obtained by filtration and separation, and the filter residue A was returned to step S1;

[0105] The filtrate A was heated to 35°C, 75 mL of a 1 mol / L sodium hydroxide solution was slowly added under normal pressure until the pH value of the reaction end point was 10, the mixture was stirred for reaction, and the second stage of impurity removal treatment was performed, and 1.2 L of the fourth filtrate (the concentration of lithium ions was 1.093 mol / L) and 41 g of the second external slag (water content 41%) were obtained by filtration and separation;

[0106] S5. The fourth filtrate was concentrated and then added with sufficient sodium carbonate to precipitate lithium to obtain an industrial grade lithium carbonate product 48.6 g and a precipitated mother liquor;

[0107] S6. The precipitated mother liquor is subjected to acid-base regeneration treatment by bipolar membrane electrodialysis technology to obtain a regenerated sulfuric acid solution (H 2 SO 4 The mass of the reaction mixture is 188 g) and regenerated sodium hydroxide solution (the mass of NaOH is 153 g), wherein the sulfuric acid solution is returned to step S4, and the sodium hydroxide solution is returned to steps S1 and S4.

[0108] Calculation shows that the recovery rate of lithium in this embodiment is 61.4%, and the recovery rate of fluorine is 49.2%.

[0109] This embodiment provides a method for comprehensive recovery of waste lithium-aluminum electrolyte, the method comprising the following steps:

[0110] S1. 1 kg of waste lithium-aluminum electrolyte powder was mixed with 771 g of solid sodium hydroxide and 6 L of water for alkaline leaching, the temperature was raised to 100 ° C, and the reaction was stirred at normal pressure for 2 h, and then filtered to obtain 5.75 L of the first filtrate and 2.02 kg of the first filter residue;

[0111] S2. The first filter residue was mixed with 40 L of water and stirred, washed with water, and after solid-liquid separation, 40.4 L of the second filtrate and 1.34 kg of the second filter residue were obtained;

[0112] S3. The first filtrate and the second filtrate were mixed and stirred, and CO was introduced at room temperature. 2 The reaction was continued until the pH value of the system was 10 after the reaction was completed, and 760 g of cryolite (after drying) and 44.7 L of the third filtrate were obtained, and the third filtrate was returned to step S2 for recycling;

[0113] S4. 1.34 kg of the second filter residue and 5 L of water were mixed and slurried to obtain a slurry; the temperature was raised to 100 ° C, and 2.6 mol of H was added to the slurry under normal pressure. 2 SO 4 The acidification reaction was carried out for 2 hours. After the acidification reaction was completed, the pH value of the system was 4. The solution was filtered and separated to obtain 5.75 L of lithium-containing leaching solution and 690 g of the first external slag (water content 25%).

[0114] The lithium-containing leachate was heated to 100° C., 450 mL of a 1 mol / L sodium hydroxide solution was slowly added under normal pressure until the pH value of the reaction end point reached 7, the mixture was stirred for reaction, and the first stage of impurity removal treatment was performed. 5.8 L of filtrate A and 850 g of filter residue A were obtained by filtration and separation, and the filter residue A was returned to step S1;

[0115] The filtrate A was heated to 100°C, 75 mL of a 1 mol / L sodium hydroxide solution was slowly added under normal pressure until the pH value of the reaction end point was 11, the mixture was stirred for reaction, and the second stage of impurity removal treatment was performed, and 5.8 L of the fourth filtrate (the concentration of lithium ions was 0.283 mol / L) and 64 g of the second external slag (water content 42%) were obtained by filtration and separation;

[0116] S5. The fourth filtrate was concentrated and then added with sufficient sodium carbonate to precipitate lithium to obtain an industrial grade lithium carbonate product 60.7g and a precipitated mother liquor;

[0117] S6. The precipitated mother liquor is subjected to acid-base regeneration treatment by bipolar membrane electrodialysis technology to obtain a regenerated sulfuric acid solution (H 2 SO 4 The mass of the reaction mixture is 284 g) and regenerated sodium hydroxide solution (the mass of NaOH is 234 g), wherein the sulfuric acid solution is returned to step S4, and the sodium hydroxide solution is returned to steps S1 and S4.

[0118] Calculations show that the recovery rate of lithium in this embodiment is 76.7%, and the recovery rate of fluorine is 78.2%.

[0119] Example 6

[0120] The difference between this embodiment and embodiment 1 is that the mass of the solid sodium hydroxide in step S1 is 193 g, and the value range of k is 0.2, and the rest is the same as embodiment 1.

[0121] Calculations show that the recovery rate of lithium in this embodiment is 30.8%, and the recovery rate of fluorine is 24.6%.

[0122] Example 7

[0123] The difference between this embodiment and embodiment 1 is that the mass of the solid sodium hydroxide in step S1 is 1542 g, the value range of k is 1.6, and the rest is the same as embodiment 1.

[0124] Calculation shows that the recovery rate of lithium in this embodiment is 13.3%, and the recovery rate of fluorine is 77.2%.

[0125] Example 8

[0126] The difference between this embodiment and embodiment 1 is that the pH value of the system after the reaction in step S3 is completed is 12, and the reaction in step S3 does not occur at this pH value. The rest is the same as embodiment 1.

[0127] Calculation shows that the recovery rate of lithium in this embodiment is 95.9%, and the recovery rate of fluorine is 0%.

[0128] Example 9

[0129] The difference between this embodiment and embodiment 1 is that the following slurry treatment is not performed in step S4: 1.5 kg of the second filter residue and 1.5 L of water are mixed and slurried to obtain slurry, and the 1.5 kg of the second filter residue and 185 mL of concentrated sulfuric acid with a mass fraction of 98% are directly subjected to acidification reaction for 2 hours, and the rest is the same as embodiment 1. It can be seen that the acidification reaction cannot be fully stirred without slurry treatment, and the obtained slurry is too thick and difficult to filter and separate.

[0130] Calculations show that the recovery rate of lithium in this embodiment is 38.3%, and the recovery rate of fluorine is 76.8%.

[0131] Comparative Example 1

[0132] The difference between this comparative example and Example 1 is that in step S3, carbon dioxide is replaced by sulfuric acid until the pH value of the system is 8 after the reaction is completed. The rest is the same as Example 1.

[0133] Comparative Example 2

[0134] This comparative example provides a method for comprehensive recovery of waste lithium-aluminum electrolytes by wet recovery. For the method, please refer to patent document CN113684369A. It can be seen that the hydroxyaluminum fluoride product obtained by adjusting the pH of the acid solution in this method cannot guarantee its purity and has a low economic value; at the same time, the technical means of evaporating and crystallizing the waste liquid to obtain the metal salt is costly and will generate large energy consumption.

[0135] In summary, the method for comprehensive recovery of waste lithium-aluminum electrolytes provided by the present invention can achieve a lithium element recovery rate of more than 95% and a fluorine element recovery rate of more than 75%, and the amount of solid waste is reduced by more than 65% during the recovery process, which has obvious economic and environmental benefits.

[0136] The applicant declares that the present invention illustrates the process method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned process steps, that is, it does not mean that the present invention must rely on the above-mentioned process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for comprehensive recovery of waste lithium-aluminum electrolyte, characterized in that: The method comprises the following steps: S1. The waste lithium-aluminum electrolyte is subjected to alkaline leaching treatment, and a first filtrate and a first filter residue are obtained after solid-liquid separation; S2. washing the first filter residue with water, and obtaining a second filtrate and a second filter residue after solid-liquid separation; S3. The first filtrate and the second filtrate are mixed, carbon dioxide is introduced to react, and cryolite and a third filtrate are obtained after solid-liquid separation; S4. The second filter residue is sequentially subjected to acid leaching treatment and two-stage impurity removal treatment to obtain a fourth filtrate; S5. The fourth filtrate is subjected to lithium precipitation treatment to obtain lithium carbonate.

2. The method according to claim 1, characterized in that The alkali leaching process in step S1 includes mixing the waste lithium-aluminum electrolyte and alkali solution; Preferably, the liquid-to-solid mass ratio of the alkali solution to the waste lithium-aluminum electrolyte is (1-7):1, preferably (3-5):1; Preferably, the mass of the solute in the alkali solution satisfies the relationship: m2=k×(3+1.82×m1), wherein m2 is the mass of the solute in the alkali solution, k is in the range of 0.3 to 0.8, preferably 0.5 to 0.7, and m1 is the mass of the fluorine element in the waste lithium-aluminum electrolyte; Preferably, the temperature of the alkali leaching treatment in step S1 is 50°C to 100°C; Preferably, the pressure of the alkali leaching treatment in step S1 is normal pressure; Preferably, the alkali leaching treatment time in step S1 is 2h to 8h.

3. The method according to claim 1 or 2, characterized in that: During the water washing process in step S2, the mass ratio of water to the waste lithium-aluminum electrolyte is (20-40):1, preferably (25-35):

1.

4. The method according to any one of claims 1 to 3, characterized in that The reaction temperature in step S3 is 25°C to 30°C; Preferably, the pH value of the system after the reaction in step S3 is 6 to 10; Preferably, the third filtrate in step S3 is returned to step S2 for recycling.

5. The method according to any one of claims 1 to 4, characterized in that The acid leaching process in step S4 includes slurrying the second filter residue to obtain slurry; and then subjecting the slurry to an acidification reaction with an acid solution; Preferably, the slurry treatment process includes mixing the second filter residue and water into slurry; Preferably, the liquid-solid mass ratio of the water to the second filter residue is (0.35-5):1; Preferably, the temperature of the acidification reaction is 25°C to 100°C; Preferably, the pressure of the acidification reaction is normal pressure; Preferably, after the acidification reaction is completed, the pH value of the system is ≤4.0, preferably 0.5-4.

6. The method according to any one of claims 1 to 5, characterized in that The two stages of impurity removal treatment in step S4 include a first stage of impurity removal treatment and a second stage of impurity removal treatment in sequence.

7. The method according to claim 6, characterized in that The first stage of impurity removal treatment comprises the steps of stirring the lithium-containing leaching solution obtained after acid leaching with an alkali solution for the first time, and obtaining a filtrate A and a filter residue A after solid-liquid separation; Preferably, the temperature of the first stirring reaction is 25°C to 100°C; Preferably, the pressure of the first stirring reaction is normal pressure; Preferably, the pH value of the system after the first stirring reaction is completed is 6-7.

8. The method according to claim 6, characterized in that The second stage of impurity removal treatment includes stirring the filtrate A and the alkali solution for a second time, and obtaining a fourth filtrate after solid-liquid separation; Preferably, the temperature of the second stirring reaction is 25°C to 100°C; Preferably, the pressure of the second stirring reaction is normal pressure; Preferably, the pH value of the second stirring reaction is 10-11.

9. The method according to any one of claims 1 to 8, characterized in that The lithium precipitation treatment process in step S5 includes adding a lithium precipitation agent; Preferably, the lithium precipitating agent comprises sodium carbonate.

10. The method according to any one of claims 1 to 9, characterized in that After the lithium precipitation treatment in step S5 is completed, the step further includes subjecting the precipitation mother liquor to acid-base regeneration treatment to obtain acid solution and alkali solution; Preferably, the acid-base regeneration treatment method includes bipolar membrane electrodialysis; Preferably, the acid solution is returned to step S4 for recycling; Preferably, the alkali solution is returned to step S1 and / or step S4 for recycling.

Images