Method for recovering iron and aluminum slag generated in battery recycling

Abstract

A method for recovering iron-aluminum slag generated in battery recycling, the method comprising the following steps: (1) mixing the iron-aluminum slag with water, obtaining water leaching residue and water leaching solution by pressurized water leaching, and washing the water leaching residue with water to obtain a lithium-rich solution; (2) low-temperature crystallization after evaporation and concentration of the lithium-rich solution, and solid-liquid separation to obtain sodium sulfate crystals and lithium precipitation mother liquor, mixing the lithium precipitation mother liquor with sodium carbonate, and solid-liquid separation to obtain lithium carbonate; (3) mixing the water leaching residue with the mother liquor, and obtaining alkali leaching residue and alkali leaching solution by pressurized alkali leaching and solid-liquid separation; (4) mixing the alkali leaching solution with a decontamination agent, and obtaining calcium fluorophosphate impurity precipitate and decontamination liquor by solid-liquid separation, and obtaining aluminum hydroxide crystals and circulating mother liquor by crystallization treatment of the decontamination liquor. The iron-aluminum slag generated in the battery recycling process is treated by pressurized leaching, realizing the comprehensive utilization of hazardous solid waste iron-aluminum slag.

Description

Technical Field

[0001] This disclosure belongs to the field of resource recycling technology and relates to a method for recycling iron and aluminum slag generated in the whole-chain integrated recycling of batteries. Background Technology

[0002] With the continuous development of the automotive power battery industry, lithium batteries have a limited cycle life, and a large number of power lithium batteries will face retirement. If left untreated, the heavy metals and organic solvents in spent lithium batteries will have a significant negative impact on the environment. Furthermore, the content of metals such as nickel, cobalt, manganese, and lithium in lithium batteries is far higher than that in primary lithium ore. Therefore, recycling spent lithium batteries at a lower cost can not only achieve considerable economic benefits but also significantly reduce environmental pressure.

[0003] Currently, the main method for recycling lithium batteries in industry is the wet leaching process. This involves discharging, dismantling, crushing, and screening waste lithium batteries before acid leaching. After acid leaching, the batteries undergo impurity removal and extraction processes to recover products such as nickel, cobalt, manganese, and lithium.

[0004] As the main product of the impurity removal process in the wet recycling of batteries, iron-aluminum slag contains a large amount of unseparated iron and aluminum compounds and a certain amount of residual lithium. Currently, iron-aluminum slag is mainly stored or outsourced as hazardous solid waste, resulting in the waste of aluminum and lithium resources and increasing unnecessary production costs.

[0005] CN105506290A discloses a method for the comprehensive utilization of iron and aluminum slag. The method involves selectively leaching the iron and aluminum slag to dissolve nickel, cobalt, and aluminum. Sodium sulfide is then added to the nickel, cobalt, and aluminum leaching solution to precipitate and recover nickel and cobalt, yielding a crude aluminum sulfate solution. The crude aluminum sulfate solution is then further treated by adding an oxidant and sodium hydroxide to remove iron, followed by the addition of sodium sulfate salt to prepare a stock solution for producing sodium aluminum sulfate. This stock solution is then evaporated and crystallized to obtain the sodium aluminum sulfate product.

[0006] CN115896462A discloses a method for recycling nickel-cobalt-iron-aluminum slag resources, belonging to the field of resource recycling technology. The method involves adding a copper-removing liquid to the nickel-cobalt-iron-aluminum slag for reaction, followed by filtration to obtain primary washed iron-aluminum slag and primary washed iron-aluminum slag liquid. Hydrogen peroxide is then added to the primary washed iron-aluminum slag liquid until a 1% potassium ferricyanide solution test shows no color, followed by the addition of a precipitant for reaction, and filtration to obtain iron-aluminum slag and iron-aluminum-removed liquid. Finally, the primary washed iron-aluminum slag, iron-aluminum slag, and water are mixed and concentrated sulfuric acid is added for reaction, followed by the addition of sodium sulfite solution for further reaction to obtain washed iron-aluminum slag and washed iron-aluminum slag liquid.

[0007] Although some aluminum and iron are recovered during the iron-aluminum slag recycling process described in the above scheme, on the one hand, the above method is complicated to operate and cannot remove sulfate ions; on the other hand, the iron-aluminum slag also contains a large amount of lithium, and if lithium is not recovered, it will result in a waste of lithium resources. Summary of the Invention

[0008] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0009] The purpose of this disclosure is to provide a method for generating iron and aluminum slag in the whole-chain integrated recycling of batteries. This disclosure achieves the separation of lithium and aluminum through pressurized water leaching + alkaline leaching process, and then obtains refined lithium carbonate, aluminum hydroxide and iron hydroxide precipitates through impurity removal, which can be made into economically viable products, thereby reducing the cost of recycling waste lithium batteries.

[0010] To achieve this objective, the present disclosure adopts the following technical solution:

[0011] In a first aspect, this disclosure provides a method for generating iron-aluminum slag in the integrated recycling of batteries across the entire supply chain, the method comprising the following steps:

[0012] (1) The iron and aluminum slag generated during battery recycling is mixed with water and subjected to pressurized water leaching to obtain water-leached slag and water-leached liquid. The water-leached slag is washed with water to obtain a lithium-rich solution.

[0013] (2) After evaporating and concentrating the lithium-rich solution obtained in step (1), crystallize it at low temperature, and separate the solid and liquid to obtain sodium sulfate crystals and lithium precipitation mother liquor. Mix the lithium precipitation mother liquor with sodium carbonate and separate the solid and liquid to obtain lithium carbonate.

[0014] (3) The water-leaching residue after washing in step (1) is mixed with the mother liquor, and then subjected to pressure alkaline leaching and solid-liquid separation to obtain alkaline leaching residue and alkaline leaching liquor.

[0015] (4) The alkaline leaching solution is mixed with the impurity removal agent, and the solid-liquid separation is performed to obtain calcium fluorophosphate impurity precipitate and impurity removal solution. The impurity removal solution is crystallized to obtain aluminum hydroxide crystals and circulating mother liquor.

[0016] This disclosure does not limit the order of operations of steps (2) and (3). Step (2) can be performed first or step (3) can be performed first.

[0017] The iron-aluminum slag produced during battery recycling contains a large amount of sodium. + SO4 2- Li leaching recovery + This disclosure describes a method for extracting valuable lithium metal from iron-aluminum slag by recycling pressurized water leaching solution, obtaining a lithium-rich solution, and then recovering and separating valuable aluminum and iron metals from the iron-aluminum slag through pressurized alkaline leaching.

[0018] In one embodiment, the solid-liquid mass ratio of the iron-aluminum slag and water in step (1) is 1:(1-5), for example: 1:1, 1:2, 1:3, 1:4 or 1:5, etc.

[0019] In one embodiment, the temperature of the pressurized water immersion is 100-300°C, for example: 100°C, 150°C, 200°C, 250°C or 300°C.

[0020] In one embodiment, the pressure of the pressurized water immersion is 0.1 to 8.5 MPa, for example: 0.1 MPa, 0.4 MPa, 1.3 MPa, 3.5 MPa, 5 MPa or 8.5 MPa, etc.

[0021] In one embodiment, the pressurized water immersion time is 0.5 to 3 hours, for example: 0.5 hours, 1 hour, 1.8 hours, 2 hours or 3 hours, etc.

[0022] In one embodiment, the liquid obtained from the washing process in step (1) is mixed with the water leaching solution to obtain a mixture. The mixture is then used to leach the iron-aluminum slag under pressure again, and this process is repeated 3-4 times to obtain a lithium-rich solution.

[0023] The equation for the reaction in step (1) of this disclosure is as follows:

[0024] 2NaFe3(SO4)2(OH)6(s)=Na2SO4(aq)+4Fe(OH)3(s)+Fe2(SO4)3(aq).

[0025] In one embodiment, the temperature of the low-temperature crystallization in step (2) is <10°C.

[0026] In one embodiment, the obtained sodium sulfate crystals are washed and dried.

[0027] In one embodiment, the detergent used for washing comprises water at a temperature <10°C.

[0028] The reaction equation for mixing the lithium precipitation mother liquor with sodium carbonate in this disclosure is as follows:

[0029] 2Li + +CO3 2- =Li2CO3.

[0030] In one embodiment, after solid-liquid separation in step (2), lithium carbonate is washed and dried.

[0031] In one embodiment, the detergent used for washing comprises water with a temperature >60°C.

[0032] In one embodiment, the mass ratio of the water-leached residue to the mother liquor in step (3) is (5-12):(20-50), for example: 5:20, 8:30, 9:15, 10:40 or 12:50, etc.

[0033] In one embodiment, the solutes in the mother liquor include sodium hydroxide and aluminum hydroxide.

[0034] In one embodiment, the caustic ratio of the mother liquor is 2 to 3, for example: 2, 2.2, 2.5, 2.8 or 3, etc., where the caustic ratio refers to the ratio of the amount of sodium oxide to aluminum oxide contained in the solution.

[0035] This disclosure employs a pressurized leaching method, which enables aluminum leaching to be achieved using a mother liquor with relatively low causticity.

[0036] In one embodiment, the temperature of the pressurized alkali leaching in step (3) is 150 to 300°C, for example: 150°C, 180°C, 200°C, 250°C or 300°C.

[0037] In one embodiment, the pressure of the pressurized alkaline leaching is 0.1 to 8.0 MPa, for example: 0.1 MPa, 0.2 MPa, 0.8 MPa, 1.2 MPa, 3.3 MPa, 5.8 MPa or 8.0 MPa, etc.

[0038] In one embodiment, the pressurized alkali immersion time is 1 to 4 hours, for example: 1 hour, 1.3 hours, 2 hours, 3 hours or 4 hours.

[0039] In one embodiment, after pressurized alkaline leaching, the temperature is lowered to below 100°C, and solid-liquid separation is performed while the liquid is still hot.

[0040] The equation for the pressurized alkali leaching described in step (3) of this disclosure is as follows:

[0041] NaAl3(SO4)2(OH)6(s)+6NaOH(aq)=2Na2SO4(aq)+3NaAlO2(aq)+6H2O

[0042] NaFe3(SO4)2(OH)6(s)+3NaOH(aq)=2Na2SO4(aq)+3Fe(OH)3(aq).

[0043] In one embodiment, after the solid-liquid separation in step (3), the alkali leaching residue is washed with water, and the resulting washing liquid is mixed with the alkali leaching liquid.

[0044] In one embodiment, the impurity remover in step (4) includes calcium hydroxide.

[0045] In one embodiment, the crystallization process includes cold water bath crystallization.

[0046] In one embodiment, after the crystallization treatment, the solid-liquid separation process is performed after the crystallization is allowed to stand for 20 to 60 hours (e.g., 20 hours, 30 hours, 40 hours, 50 hours, or 60 hours).

[0047] The impurity removal process in step (4) of this disclosure can remove impurity elements such as F and P from the alkaline leaching solution. The reaction equation for impurity removal is as follows:

[0048] 2F - +Ca 2+ →CaF2↓;

[0049] 2PO4 3- +3Ca 2+ →Ca3(PO4)2↓

[0050] 3Ca3(PO4)2+CaF2→3Ca3(PO4)2·CaF2↓.

[0051] In one embodiment, the circulating mother liquor in step (4) is used for the pressurized alkaline leaching in step (3).

[0052] Compared with the prior art, this disclosure has the following beneficial effects:

[0053] (1) This disclosure achieves the comprehensive utilization of hazardous solid waste iron and aluminum slag by pressurizing the leaching treatment of the iron and aluminum slag generated during the battery recycling process. By recycling the pressurized water leaching solution of the iron and aluminum slag, valuable lithium metal in the iron and aluminum slag is extracted to obtain a lithium-rich solution. Valuable aluminum metal in the iron and aluminum slag is recovered by pressurized alkaline leaching. They can be made into economically beneficial products, thereby reducing the cost of recycling waste lithium batteries.

[0054] (2) After the iron-aluminum slag is recycled by the process disclosed herein, the Li leaching rate can reach more than 91%, the Na2SO4 recovery rate can reach more than 90%, and the Al leaching rate can reach more than 84%, which can efficiently recover Li, Al elements and sodium sulfate from the iron-aluminum slag.

[0055] After reading and understanding the accompanying diagrams and detailed descriptions, the other aspects can be understood. Attached Figure Description

[0056] The accompanying drawings are used to provide a further understanding of the technical solutions in this paper and form part of the specification. They are used together with the embodiments of this application to explain the technical solutions in this paper and do not constitute a limitation on the technical solutions in this paper.

[0057] Figure 1 This is a process flow diagram of the method described in one embodiment of this disclosure. Detailed Implementation

[0058] The technical solutions of this disclosure will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of this disclosure and should not be construed as specific limitations thereof.

[0059] The elemental content of iron and aluminum slag generated during battery recycling in the embodiments and comparative examples of this disclosure is shown in Table 1:

[0060] Table 1

[0061] Na content / % S content / % Al content / % Li content / % 7.44％ 7.05％ 5.02％ 0.11％

[0062] Example 1

[0063] This embodiment provides a method for the integrated recycling of iron and aluminum slag generated during battery recycling across the entire supply chain. A flowchart of the method is shown below. Figure 1 As shown, the method includes the following steps:

[0064] (1) Mix the iron and aluminum slag generated during battery recycling with water to form a slurry, and control the solid-liquid mass ratio to be 1:1. Put the slurry into a high-pressure kettle for pressure leaching. The pressure leaching temperature is 300℃ and the leaching time is 3h. After leaching, filter and separate the water-leached residue and water-leached liquid. Use 100mL of pure water to wash the water-leached residue. Mix the liquid and water-leached liquid and return it to the next pressure leaching step before mixing it with the iron and aluminum slag raw material for pressure leaching. After 3-4 cycles, a lithium-rich solution is obtained.

[0065] (2) The obtained lithium-rich solution is evaporated and concentrated, frozen (temperature below 10℃) for crystallization, filtered, and sodium sulfate crystals with low impurity content and lithium precipitation mother liquor are obtained. The sodium sulfate crystals are washed with a small amount of pure water at a temperature below 10℃ to remove residual solution, filtered and dried. Sodium carbonate is added to the lithium precipitation mother liquor, and after sufficient precipitation, it is filtered to obtain crude lithium carbonate. The crude lithium carbonate is washed with a small amount of pure water at a temperature above 60℃ to remove residual impurities, filtered and dried to obtain refined lithium carbonate.

[0066] (3) Take 50g of water leaching residue and mix it with 250g of mother liquor with a caustic ratio of 3.0. Put it into a high pressure vessel for pressure leaching. Set the pressure leaching temperature to 300℃ and the leaching time to 3h. After leaching, wait for the temperature inside the vessel to drop below 100℃, filter while hot, and separate the alkali leaching residue and alkali leaching liquid. Take 50mL of pure water to wash the alkali leaching residue and mix the washing liquid with the alkali leaching liquid.

[0067] (4) Add the impurity removal agent Ca(OH)2 to the alkaline leaching solution and stir for 2 hours to obtain calcium fluorophosphate impurity precipitate. Separate the impurity removal solution and perform cold water bath crystallization. After standing for 48 hours, filter and separate to obtain circulating mother liquor and Al(OH)3 crystals. The circulating mother liquor can be returned to the pressurized alkaline leaching process for recycling.

[0068] Example 2

[0069] This embodiment provides a method for the integrated recycling of iron and aluminum slag generated during battery recycling across the entire supply chain. A flowchart of the method is shown below. Figure 1 As shown, the method includes the following steps:

[0070] (1) Mix the iron and aluminum slag generated during battery recycling with water to form a slurry, and control the solid-liquid mass ratio to be 2:1. Put the slurry into a high-pressure kettle for pressure leaching. The pressure leaching temperature is 250℃ and the leaching time is 2h. After leaching, filter and separate the water-leached residue and water-leached liquid. Use 100mL of pure water to wash the water-leached residue. Mix the liquid and water-leached liquid and return it to the next pressure leaching step before mixing it with the iron and aluminum slag raw material for pressure leaching. After 3-4 cycles, a lithium-rich solution is obtained.

[0071] (2) The obtained lithium-rich solution is evaporated and concentrated, frozen (temperature below 10℃) for crystallization, filtered, and sodium sulfate crystals with low impurity content and lithium precipitation mother liquor are obtained. The sodium sulfate crystals are washed with a small amount of pure water at a temperature below 10℃ to remove residual solution, filtered and dried. Sodium carbonate is added to the lithium precipitation mother liquor, and after sufficient precipitation, it is filtered to obtain crude lithium carbonate. The crude lithium carbonate is washed with a small amount of pure water at a temperature above 60℃ to remove residual impurities, filtered and dried to obtain refined lithium carbonate.

[0072] (3) Take 50g of water leaching residue and mix it with 300g of mother liquor with a caustic ratio of 2. Put it into a high pressure vessel for pressure leaching. Set the pressure leaching temperature to 250℃ and the leaching time to 3h. After leaching, wait for the temperature inside the vessel to drop below 100℃, filter while hot, and separate the alkali leaching residue and alkali leaching liquid. Take 50mL of pure water to wash the alkali leaching residue and mix the washing liquid with the alkali leaching liquid.

[0073] (4) Add the impurity removal agent Ca(OH)2 to the alkaline leaching solution and stir for 2 hours to obtain calcium fluorophosphate impurity precipitate. Separate the impurity removal solution and perform cold water bath crystallization. After standing for 48 hours, filter and separate to obtain circulating mother liquor and Al(OH)3 crystals. The circulating mother liquor can be returned to the pressurized alkaline leaching process for recycling.

[0074] Example 3

[0075] This embodiment provides a method for the integrated recycling of iron and aluminum slag generated during battery recycling across the entire supply chain. A flowchart of the method is shown below. Figure 1 As shown, the method includes the following steps:

[0076] (1) Mix the iron and aluminum slag generated during battery recycling with water to form a slurry, and control the solid-liquid mass ratio to 1:5. Put the slurry into a high-pressure kettle for pressure leaching. The pressure leaching temperature is 100℃ and the leaching time is 3h. After leaching, filter and separate the water-leached residue and water-leached liquid. Use 50mL of pure water to wash the water-leached residue. Mix the liquid and water-leached liquid and return it to the next pressure leaching step. Mix it with the iron and aluminum slag raw material for pressure leaching. After 3-4 cycles, a lithium-rich solution is obtained.

[0077] (2) The obtained lithium-rich solution is evaporated and concentrated, frozen (temperature below 10℃) for crystallization, filtered, and sodium sulfate crystals with low impurity content and lithium precipitation mother liquor are obtained. The sodium sulfate crystals are washed with a small amount of pure water at a temperature below 10℃ to remove residual solution, filtered and dried. Sodium carbonate is added to the lithium precipitation mother liquor, and after sufficient precipitation, it is filtered to obtain crude lithium carbonate. The crude lithium carbonate is washed with a small amount of pure water at a temperature above 60℃ to remove residual impurities, filtered and dried to obtain refined lithium carbonate.

[0078] (3) Take 120g of water leaching residue and mix it with 500g of mother liquor with a caustic ratio of 2.5. Put it into a high pressure vessel for pressure leaching. Set the pressure leaching temperature to 150℃ and the leaching time to 3h. After leaching, wait for the temperature inside the vessel to drop below 100℃. Filter while hot to separate the alkali leaching residue and alkali leaching liquid. Take 50mL of pure water to wash the alkali leaching residue and mix the washing liquid with the alkali leaching liquid.

[0079] (4) Add the impurity removal agent Ca(OH)2 to the alkaline leaching solution and stir for 2 hours to obtain calcium fluorophosphate impurity precipitate. Separate the impurity removal solution and perform cold water bath crystallization. After standing for 48 hours, filter and separate to obtain circulating mother liquor and Al(OH)3 crystals. The circulating mother liquor can be returned to the pressurized alkaline leaching process for recycling.

[0080] Example 4

[0081] The only difference between this embodiment and Embodiment 1 is that the temperature of the pressurized water immersion is 400℃, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0082] Example 5

[0083] The only difference between this embodiment and Embodiment 1 is that the temperature of the pressurized alkali leaching is 120°C, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0084] Example 6

[0085] The only difference between this embodiment and Embodiment 1 is that the temperature of the pressurized alkali leaching is 400℃, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0086] Comparative Example 1

[0087] This comparative example provides a method for recycling iron-aluminum slag generated during battery recycling, the method comprising the following steps:

[0088] (1) Mix the solid waste iron and aluminum slag from battery recycling with pure water to form a slurry. Control the solid-liquid mass ratio to 1:1. The slurry is heated and leached in a beaker in a water bath at a temperature of 95°C for 3 hours. After leaching, filter and separate the leached residue and the leached liquid. Use 100ml of pure water to wash the leached residue. Mix the washing liquid with the leached liquid and return it to the next pressurized water leaching step before mixing it with the iron and aluminum slag raw material for water leaching. After 3-4 cycles, a lithium-rich solution is obtained.

[0089] (2) The obtained lithium-rich solution was evaporated and concentrated, then frozen (at a temperature below 10°C) to crystallize, and filtered to obtain sodium sulfate crystals with low impurity content and lithium precipitation mother liquor. The sodium sulfate crystals were washed with a small amount of pure water at a temperature below 10°C to remove residual solution, filtered, and dried.

[0090] (3) Take 50g of water leaching residue and mix it with 250g of mother liquor with a caustic ratio of 3.0. Put it into a beaker and heat it in a water bath. Set the leaching temperature to 95℃ and the leaching time to 3h. After leaching, filter it while it is hot to separate the alkali leaching residue and alkali leaching liquid. Take 50mL of pure water to wash the alkali leaching residue and mix the washing liquid with the alkali leaching liquid.

[0091] (4) Add the impurity removal agent Ca(OH)2 to the alkaline leaching solution and stir for 2 hours to obtain calcium fluorophosphate impurity precipitate. Separate the impurity removal solution and perform cold water bath crystallization. After standing for 48 hours, filter and separate to obtain circulating mother liquor and crude Al(OH)3 crystals.

[0092] Performance testing:

[0093] The leaching rates of each element during the water leaching and alkali leaching processes described in the examples and comparative examples are shown in Table 2:

[0094] Table 2

[0095]

[0096]

[0097] As shown in Table 2, based on Examples 1-6, after the iron-aluminum slag is recycled using the process disclosed in this invention, the Li leaching rate can reach over 91%, the Na2SO4 recovery rate can reach over 90%, and the Al leaching rate can reach over 84%. This process can efficiently recover Li, Al elements, and sodium sulfate from the iron-aluminum slag. At higher leaching temperatures, the leaching rates of Li, Na2SO4, and Al are higher, and less water and mother liquor are required. Therefore, experimental resources can be utilized efficiently.

[0098] A comparison of Examples 1 and 4 shows that the temperature of pressurized water immersion affects the recovery effect during the recovery process described in this disclosure. Controlling the temperature of pressurized water immersion between 100 and 300°C results in a better recovery effect. If the temperature of pressurized water immersion is too high, the improvement in the leaching rate of elements will be small, and the utilization rate of electrical energy will be low.

[0099] A comparison of Examples 1 and 5-6 shows that the temperature of pressurized alkaline leaching affects the recovery effect during the recovery process described in this disclosure. Controlling the temperature of pressurized alkaline leaching at 150-300℃ results in a better recovery effect. If the temperature of pressurized alkaline leaching is too low, the reaction time is longer and the leaching rate of Al is lower. If the temperature of pressurized alkaline leaching is too high, the improvement in the leaching rate of elements is smaller and the energy utilization rate is lower.

[0100] As can be seen from the comparison between Example 1 and Comparative Example 1, this disclosure uses a pressurized method combined with water immersion and alkaline immersion to separate lithium and aluminum. Then, through impurity removal, refined lithium carbonate, aluminum hydroxide and iron hydroxide precipitates are obtained, which can be made into economically viable products, reducing the cost of recycling waste lithium batteries.

Claims

1.A method for recovering iron-aluminum slag generated in a full-chain integrated battery recycling process, the method comprising the following steps: (1) mixing the iron-aluminum slag generated in the battery recycling process with water, obtaining water leaching residue and water leaching solution by pressurized water leaching, washing the water leaching residue with water, mixing the washing liquid obtained in step (1) with the water leaching solution to obtain a mixed solution, and repeating the pressurized water leaching of the iron-aluminum slag with the mixed solution for 3-4 times to obtain a lithium-rich solution; the pressure of the pressurized water leaching is 0.1-8.5 MPa; (2) evaporating and concentrating the lithium-rich solution obtained in step (1) to obtain sodium sulfate crystals and a lithium precipitation mother liquor by low-temperature crystallization, and separating the sodium sulfate crystals and the lithium precipitation mother liquor to obtain lithium carbonate by mixing the lithium precipitation mother liquor with sodium carbonate; (3) mixing the water leaching residue after the washing treatment in step (1) with a mother liquor, and obtaining alkali leaching residue and alkali leaching solution by pressurized alkali leaching and solid-liquid separation; the caustic ratio of the mother liquor is 2-3; the pressure of the pressurized alkali leaching is 0.1-8.0 MPa; the alkali leaching residue is washed with water after the solid-liquid separation in step (3) to obtain washing liquid, and the washing liquid is mixed with the alkali leaching solution; (4) mixing the alkali leaching solution with a decontamination agent, and separating calcium fluorophosphate impurities and decontamination mother liquor to obtain aluminum hydroxide crystals and a circulating mother liquor by crystallization treatment of the decontamination mother liquor; wherein the order of steps (2) and (3) is not limited; the solid-liquid mass ratio of the iron-aluminum slag and water in step (1) is 1:(1-5); the temperature of the pressurized water leaching is 100-300℃; the time of the pressurized water leaching is 0.5-3 h; the temperature of the low-temperature crystallization in step (2) is <10℃; the sodium sulfate crystals obtained in step (2) are washed and dried; the washing agent for the washing includes water with a temperature of <10℃; the lithium carbonate is washed and dried after the solid-liquid separation in step (2); the washing agent for the washing includes water with a temperature of >60℃; the mass ratio of the water leaching residue and the mother liquor in step (3) is (5-12):(20-50); the solutes of the mother liquor include sodium hydroxide and aluminum hydroxide; the temperature of the pressurized alkali leaching in step (3) is 150-300℃; the time of the pressurized alkali leaching is 1-4 h; the temperature is reduced to below 100℃ after the pressurized alkali leaching, and the solid-liquid separation is performed while the temperature is high; the decontamination agent in step (4) includes calcium hydroxide; the crystallization treatment includes cold water bath crystallization; the solid-liquid separation is performed after the crystallization treatment and the standing for 20-60 h; and the circulating mother liquor in step (4) is used for the pressurized alkali leaching in step (3). ​ ​ ​ ​ ​ ​ 2. The method of claim 1, wherein, ​ 3. The method of claim 1, wherein, ​ 4. The method of claim 1, wherein, ​ 5. The method of claim 1, wherein, ​ ​ 6. The method of claim 1, wherein, ​ 7. The method of claim 1, wherein, ​ 8. The method of claim 1, wherein, ​ 9. The method of claim 1, wherein, ​ 10. The method of claim 1, wherein, ​ 11. The method of claim 1, wherein, ​ 12. The method of claim 1, wherein, ​ 13. The method of claim 1, wherein, ​ 14. The method of claim 1, wherein, ​ 15. The method of claim 1, wherein, ​

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