Method for full-chain integrated recovery of iron-aluminum slag produced during battery recycling

Abstract

A method for full-chain integrated recovery of iron-aluminum slag produced during battery recycling. The method comprises the following steps: (1) mixing iron-aluminum slag with water, carrying out pressurized leaching with water, so as to obtain water leaching residues and a water leachate, and using water to wash the water leaching residues, so as to obtain a lithium-rich solution; (2) evaporating and concentrating the lithium-rich solution, then carrying out low-temperature crystallization, performing solid-liquid separation to obtain sodium sulfate crystals and a lithium precipitation mother liquor, mixing the lithium precipitation mother liquor with sodium carbonate and performing solid-liquid separation to obtain lithium carbonate; (3) mixing the water leaching residues with the mother liquor, carrying out pressurized alkali leaching and performing solid-liquid separation to obtain alkali-leaching residues and a leachate of alkali leaching; and (4) mixing the leachate of alkali leaching with an impurity remover, and performing solid-liquid separation to obtain calcium fluorophosphate impurity precipitate and an impurity-removed purified solution, and crystallizing the impurity-removed purified solution, so as to obtain aluminum hydroxide crystals and a mother liquor for recycling. Pressurized leaching of iron-aluminum slag generated during battery recycling achieves comprehensive resource utilization of the hazardous solid waste iron-aluminum slag.

Description

A full-chain integrated method for recycling iron and aluminum slag produced in battery recycling Technical Field

[0001] The present disclosure belongs to the technical field of resource recovery and relates to a method for recycling iron and aluminum slag produced in battery recycling in an integrated full-chain manner. Background Art

[0002] As the automotive power battery industry continues to develop, lithium batteries face limited cycle life, necessitating the retirement of a significant number of them. Left untreated, the heavy metals and organic solvents in spent lithium batteries can have significant environmental impacts. Furthermore, the concentrations of metals like nickel, cobalt, manganese, and lithium in lithium batteries are far higher than those in primary ore. Therefore, recycling spent lithium batteries at a lower cost not only yields substantial economic benefits but also significantly reduces environmental impact.

[0003] Currently, the main industrial method for recycling lithium batteries is the wet leaching process, which involves discharging, disassembling, crushing, screening, and then acid leaching. After acid leaching, the batteries are then subjected to impurity removal and extraction processes to recover nickel, cobalt, manganese, lithium and other products.

[0004] Ferroaluminum slag is the main product of the impurity removal process in the wet recycling of batteries. A large amount of iron and aluminum compounds in the ferroaluminum slag are not separated and a certain amount of lithium elements remain in the slag. At present, ferroaluminum slag is mainly stored or outsourced as hazardous solid waste, resulting in waste of aluminum and lithium resources and increasing unnecessary production costs.

[0005] CN105506290A discloses a method for comprehensive utilization of iron-aluminum slag, which comprises selectively leaching the iron-aluminum slag to dissolve nickel, cobalt, and aluminum in the slag; then adding sodium sulfide to the nickel, cobalt, and aluminum leaching solution to precipitate and recover the nickel and cobalt in the solution to obtain a crude aluminum sulfate solution; adding an oxidant and sodium hydroxide to the crude aluminum sulfate solution to remove iron, and then adding sodium sulfate salt to prepare the solution into a stock solution for producing sodium aluminum sulfate; and evaporating and crystallizing the stock solution to obtain a sodium aluminum sulfate product.

[0006] CN115896462A discloses a method for recycling nickel-cobalt-containing ferro-aluminum slag resources, belonging to the technical field of resource recycling and utilization. The method comprises the following steps: adding a copper removal liquid to the nickel-cobalt-containing ferro-aluminum slag for reaction, and filtering to obtain a primary ferro-aluminum slag and a primary ferro-aluminum slag liquid; then adding hydrogen peroxide to the primary ferro-aluminum slag liquid until a 1% potassium ferrocyanide solution is colorless, and then adding a precipitant for reaction, and filtering to obtain ferro-aluminum slag and a de-ironized aluminum liquid; finally, the primary ferro-aluminum slag, the ferro-aluminum slag, and water are mixed, and concentrated sulfuric acid is added to react, and then a sodium sulfite solution is added to react to obtain the ferro-aluminum slag and the ferro-aluminum slag liquid.

[0007] Although part of the aluminum and iron are recovered during the recovery process of the iron-aluminum slag 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. If the lithium is not recovered, it will cause a waste of lithium resources.

[0008] Summary of the Invention

[0009] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0010] The purpose of the present disclosure is to provide a full-chain integrated method for recycling iron-aluminum slag produced in battery recycling. The present disclosure realizes the separation of lithium and aluminum through pressurized water leaching + alkaline leaching process, and then obtains refined lithium carbonate, aluminum hydroxide and iron hydroxide precipitate by impurity removal, which can be made into economically profitable products respectively, thereby reducing the cost of recycling waste lithium batteries.

[0011] To achieve this purpose, the present disclosure adopts the following technical solutions:

[0012] In a first aspect, the present disclosure provides a method for recycling iron and aluminum slag produced in battery recycling in a full-chain integrated manner, the method comprising the following steps:

[0013] (1) mixing the iron-aluminum slag produced in battery recovery with water, subjecting the mixture to pressurized water immersion to obtain water-leached slag and water-leached liquid, and washing the water-leached slag with water to obtain a lithium-rich solution;

[0014] (2) evaporating and concentrating the lithium-rich solution obtained in step (1) and then subjecting it to low-temperature crystallization, performing solid-liquid separation to obtain sodium sulfate crystals and a lithium precipitation mother liquor, mixing the lithium precipitation mother liquor with sodium carbonate, and subjecting it to solid-liquid separation to obtain lithium carbonate;

[0015] (3) mixing the water leaching residue after the washing treatment in step (1) with the mother liquor, subjecting the mixture to pressurized alkali leaching, and performing solid-liquid separation to obtain alkali leaching residue and alkali leaching liquid;

[0016] (4) mixing the alkaline leaching solution with the impurity remover, performing solid-liquid separation to obtain calcium fluorophosphate impurity precipitate and impurity-removing liquid, and performing crystallization treatment on the impurity-removing liquid to obtain aluminum hydroxide crystals and circulating mother liquor.

[0017] The present disclosure does not limit the order of operations of step (2) and step (3), and step (2) or step (3) can be performed first.

[0018] The iron and aluminum slag produced in battery recycling contains a large amount of Na + 、SO4 2- , leaching recovery of Li +The present invention extracts valuable metal lithium from the ferroaluminum slag by recycling pressurized water leaching liquid to obtain a lithium-rich solution, and recovers and separates the valuable metal aluminum and iron in the ferroaluminum slag through pressurized alkaline leaching.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] In one embodiment, the liquid obtained by the washing treatment in step (1) is mixed with the water leaching liquid to obtain a mixed liquid, and the iron-aluminum slag is again pressurized and water-leached using the mixed liquid, and the mixture is repeated 3-4 times to obtain a lithium-rich solution.

[0024] The reaction equation of the method of step (1) of the present disclosure is as follows: 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 washing detergent comprises water at a temperature < 10°C.

[0028] The reaction equation of mixing the lithium precipitation mother liquor with sodium carbonate is as follows: + +CO3 2- =Li2CO3.

[0029] In one embodiment, the lithium carbonate is washed and dried after the solid-liquid separation in step (2).

[0030] In one embodiment, the washing detergent comprises water at a temperature > 60°C.

[0031] 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.

[0032] In one embodiment, the solute of the mother liquor comprises sodium hydroxide and aluminum hydroxide.

[0033] 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. The caustic ratio refers to the ratio of the amount of sodium oxide to aluminum oxide contained in the solution.

[0034] The present disclosure adopts a pressurized method for leaching, and can achieve aluminum leaching under the condition of using a mother liquor with relatively low causticity.

[0035] In one embodiment, the temperature of the pressurized alkali leaching in step (3) is 150-300°C, for example, 150°C, 180°C, 200°C, 250°C or 300°C.

[0036] In one embodiment, the pressure of the pressurized alkali 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.

[0037] In one embodiment, the pressurized alkali leaching time is 1 to 4 hours, for example, 1 hour, 1.3 hours, 2 hours, 3 hours or 4 hours.

[0038] In one embodiment, the temperature is lowered to below 100° C. after the pressurized alkali leaching, and solid-liquid separation is performed while hot.

[0039] The equation for the pressure alkali leaching in step (3) of the present disclosure is as follows: NaAl3(SO4)2(OH)6(s)+6NaOH(aq)=2Na2SO4(aq)+3NaAlO2(aq)+6H2O NaFe3(SO4)2(OH)6(s)+3NaOH(aq)=2Na2SO4(aq)+3Fe(OH)3(aq).

[0040] In one embodiment, after the solid-liquid separation in step (3), the alkali leaching residue is washed with water, and the obtained washing liquid is mixed with the alkali leaching liquid.

[0041] In one embodiment, the impurity remover in step (4) comprises calcium hydroxide.

[0042] In one embodiment, the crystallization treatment comprises cold water bath crystallization.

[0043] In one embodiment, after the crystallization treatment, the product is allowed to stand for 20 to 60 hours (eg, 20 hours, 30 hours, 40 hours, 50 hours, or 60 hours) before undergoing solid-liquid separation treatment.

[0044] The impurity removal process in step (4) of the present disclosure can remove impurity elements such as F and P in the alkaline leaching solution. The reaction equation for impurity removal is as follows: - +Ca 2+ →CaF2↓; 2PO4 3- +3Ca 2+ →Ca3(PO4)2↓ 3Ca3(PO4)2+CaF2→3Ca3(PO4)2·CaF2↓.

[0045] In one embodiment, the circulating mother liquor in step (4) is used for the pressurized alkali leaching in step (3).

[0046] Compared with the prior art, the present disclosure has the following beneficial effects:

[0047] (1) The present invention realizes the comprehensive resource utilization of the hazardous solid waste iron-aluminum slag by subjecting it to pressure leaching treatment. By recycling the pressurized water leaching liquid of the iron-aluminum slag, the valuable metal lithium in the iron-aluminum slag is extracted to obtain a lithium-rich solution. By pressurized alkaline leaching, the valuable metal aluminum in the iron-aluminum slag is recovered and can be made into economically profitable products respectively, thereby reducing the cost of recycling waste lithium batteries.

[0048] (2) After the ferroaluminum slag is recovered by the process disclosed in the present invention, 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 the Li, Al elements and sodium sulfate in the ferroaluminum slag.

[0049] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0051] FIG1 is a process flow chart of a method according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0052] The technical solution of the present disclosure is further described below through specific implementation methods. It should be understood by those skilled in the art that the embodiments are only used to help understand the present disclosure and should not be regarded as specific limitations of the present disclosure.

[0053] The element contents of the iron and aluminum slag produced during battery recycling used in the embodiments and comparative examples of the present disclosure are shown in Table 1:

[0054] Table 1

[0055] Example 1

[0056] This embodiment provides a method for recycling iron and aluminum slag produced in battery recycling in a full-chain integrated manner. The process diagram of the method is shown in FIG1 . The method comprises the following steps:

[0057] (1) The iron-aluminum slag produced in battery recycling is mixed with water to prepare a slurry, and the solid-liquid mass ratio is controlled to be 1:1. The slurry is placed in an autoclave for pressure leaching. The pressure leaching temperature is 300°C and the leaching time is 3 hours. After the leaching is completed, the water-leached slag and the water-leaching liquid are obtained by filtration and separation. The water-leached slag is washed with 100 mL of pure water. The obtained liquid is mixed with the water-leaching liquid and returned to the next pressure leaching step before being mixed with the iron-aluminum slag raw material for pressure leaching. After 3-4 cycles, a lithium-rich solution is obtained;

[0058] (2) evaporating and concentrating the obtained lithium-rich solution, freezing (temperature below 10°C) for crystallization, and filtering to obtain sodium sulfate crystals with low impurity content and lithium precipitation mother liquor, washing the sodium sulfate crystals with a small amount of pure water at a temperature below 10°C to remove the residual solution, filtering and drying, adding sodium carbonate to the lithium precipitation mother liquor, filtering after sufficient precipitation to obtain crude lithium carbonate, washing the crude lithium carbonate with a small amount of pure water above 60°C to remove residual impurities, filtering and drying to obtain refined lithium carbonate;

[0059] (3) 50 g of water-leached residue was mixed with 250 g of mother liquor with a caustic ratio of 3.0, and placed in an autoclave for pressure leaching. The pressure leaching temperature was set to 300 ° C and the leaching time was 3 h. After the leaching was completed, the temperature in the autoclave dropped below 100 ° C, and the alkali leaching residue and the alkali leaching liquid were separated by hot filtration. 50 mL of pure water was used to wash the alkali leaching residue, and the washing liquid was mixed with the alkali leaching liquid;

[0060] (4) Add impurity remover Ca(OH)2 to the alkaline leaching solution and stir for 2 hours to obtain calcium fluorophosphate impurity precipitate, separate and obtain impurity-removed semen, and crystallize the impurity-removed semen in a cold water bath. 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.

[0061] Example 2

[0062] This embodiment provides a method for recycling iron and aluminum slag produced in battery recycling in a full-chain integrated manner. The process diagram of the method is shown in FIG1 . The method comprises the following steps:

[0063] (1) The iron-aluminum slag produced in battery recycling is mixed with water to prepare a slurry, and the solid-liquid mass ratio is controlled to be 2:1. The slurry is placed in an autoclave for pressure leaching. The pressure leaching temperature is 250°C and the leaching time is 2 hours. After the leaching is completed, the water-leached slag and the water-leaching liquid are separated by filtration. The water-leached slag is washed with 100 mL of pure water. The obtained liquid is mixed with the water-leaching liquid and returned to the next pressure leaching step before being mixed with the iron-aluminum slag raw material for pressure leaching. After 3-4 cycles, a lithium-rich solution is obtained;

[0064] (2) evaporating and concentrating the obtained lithium-rich solution, freezing (temperature below 10°C) for crystallization, and filtering to obtain sodium sulfate crystals with low impurity content and lithium precipitation mother liquor, washing the sodium sulfate crystals with a small amount of pure water at a temperature below 10°C to remove the residual solution, filtering and drying, adding sodium carbonate to the lithium precipitation mother liquor, filtering after sufficient precipitation to obtain crude lithium carbonate, washing the crude lithium carbonate with a small amount of pure water above 60°C to remove residual impurities, filtering and drying to obtain refined lithium carbonate;

[0065] (3) 50 g of water-leached residue was mixed with 300 g of mother liquor with a caustic ratio of 2, and the mixture was placed in an autoclave for pressure leaching. The pressure leaching temperature was set to 250 ° C and the leaching time was 3 h. After the leaching was completed, the temperature in the autoclave was lowered to below 100 ° C, and the mixture was filtered while hot to separate the alkali leaching residue and the alkali leaching liquid. 50 mL of pure water was used to wash the alkali leaching residue, and the washing liquid was mixed with the alkali leaching liquid;

[0066] (4) Add impurity remover Ca(OH)2 to the alkaline leaching solution and stir for 2 hours to obtain calcium fluorophosphate impurity precipitate, separate and obtain impurity-removed semen, and crystallize the impurity-removed semen in a cold water bath. 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.

[0067] Example 3

[0068] This embodiment provides a method for recycling iron and aluminum slag produced in battery recycling in a full-chain integrated manner. The process diagram of the method is shown in FIG1 . The method comprises the following steps:

[0069] (1) The iron-aluminum slag produced in battery recycling is mixed with water to prepare a slurry, and the solid-liquid mass ratio is controlled to be 1:5. The slurry is placed in an autoclave for pressure leaching. The pressure leaching temperature is 100°C and the leaching time is 3 hours. After the leaching is completed, the water-leached slag and the water-leaching liquid are separated by filtration. The water-leached slag is washed with 50 mL of pure water. The obtained liquid is mixed with the water-leaching liquid and returned to the next pressure leaching step before being mixed with the iron-aluminum slag raw material for pressure leaching. After 3-4 cycles, a lithium-rich solution is obtained;

[0070] (2) evaporating and concentrating the obtained lithium-rich solution, freezing (temperature below 10°C) for crystallization, and filtering to obtain sodium sulfate crystals with low impurity content and lithium precipitation mother liquor, washing the sodium sulfate crystals with a small amount of pure water at a temperature below 10°C to remove the residual solution, filtering and drying, adding sodium carbonate to the lithium precipitation mother liquor, filtering after sufficient precipitation to obtain crude lithium carbonate, washing the crude lithium carbonate with a small amount of pure water above 60°C to remove residual impurities, filtering and drying to obtain refined lithium carbonate;

[0071] (3) 120 g of water-leached residue was mixed with 500 g of mother liquor with a caustic ratio of 2.5, and placed in an autoclave for pressure leaching. The pressure leaching temperature was set to 150 ° C and the leaching time was 3 h. After the leaching was completed, the temperature in the autoclave dropped to below 100 ° C, and the alkali leaching residue and the alkali leaching liquid were separated while hot. 50 mL of pure water was used to wash the alkali leaching residue, and the washing liquid was mixed with the alkali leaching liquid;

[0072] (4) Add impurity remover Ca(OH)2 to the alkaline leaching solution and stir for 2 hours to obtain calcium fluorophosphate impurity precipitate, separate and obtain impurity-removed semen, and crystallize the impurity-removed semen in a cold water bath. 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.

[0073] Example 4

[0074] The only difference between this embodiment and embodiment 1 is that the temperature of the pressurized water immersion is 400° C., and the other conditions and parameters are exactly the same as those in embodiment 1.

[0075] Example 5

[0076] The only difference between this embodiment and embodiment 1 is that the temperature of the pressurized alkali leaching is 120° C., and the other conditions and parameters are exactly the same as those in embodiment 1.

[0077] Example 6

[0078] The only difference between this embodiment and embodiment 1 is that the temperature of the pressurized alkali leaching is 400° C., and the other conditions and parameters are exactly the same as those in embodiment 1.

[0079] Comparative Example 1

[0080] This comparative example provides a method for recovering iron-aluminum slag produced during battery recycling, the method comprising the following steps:

[0081] (1) The battery recycled solid waste iron and aluminum slag is mixed with pure water to prepare a slurry, and the solid-liquid mass ratio is controlled to be 1:1. The slurry is heated in a water bath in a beaker for leaching, the leaching temperature is 95°C, and the leaching time is 3 hours. After the leaching is completed, the water leaching residue and the water leaching liquid are separated by filtration. The water leaching residue is washed with 100 ml of pure water. The washing liquid and the water leaching liquid are mixed and returned to the next pressurized water leaching step before mixing with the iron and aluminum slag raw material for water leaching. After 3-4 cycles, a lithium-rich solution is obtained;

[0082] (2) Evaporating and concentrating the obtained lithium-rich solution, freezing (temperature below 10°C) for crystallization, and filtering to obtain sodium sulfate crystals with low impurity content and lithium precipitation mother liquor. The sodium sulfate crystals are washed with a small amount of pure water at a temperature below 10°C to remove the residual solution, filtered, and dried;

[0083] (3) 50 g of water-leached residue was mixed with 250 g of mother liquor with a caustic ratio of 3.0, placed in a beaker and heated in a water bath. The leaching temperature was set to 95 ° C and the leaching time was 3 h. After the leaching was completed, the alkali leaching residue and the alkali leaching liquid were separated by hot filtration. 50 mL of pure water was used to wash the alkali leaching residue, and the washing liquid was mixed with the alkali leaching liquid;

[0084] (4) Add impurity remover Ca(OH)2 to the alkaline leaching solution and stir for 2 hours to obtain calcium fluorophosphate impurity precipitate, which is separated to obtain impurity-removed semen. The impurity-removed semen is crystallized in a cold water bath, and after standing for 48 hours, it is filtered and separated to obtain circulating mother liquor and crude Al(OH)3 crystals.

[0085] Performance testing:

[0086] In the methods described in the examples and comparative examples, the leaching rates of the elements during water leaching and alkali leaching are shown in Table 2:

[0087] Table 2

[0088] As can be seen from Table 2, according to Examples 1-6, after the ferroaluminum slag is recovered 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%. Li, Al elements and sodium sulfate in the ferroaluminum slag can be efficiently recovered. When the leaching temperature is high, the Li, Na2SO4, and Al leaching rates are high, and less water and mother liquor are required, so that experimental resources can be used efficiently.

[0089] By comparing Example 1 and Example 4, it can be seen that in the recovery process described in the present disclosure, the temperature of the pressurized water immersion will affect the recovery effect. When the temperature of the pressurized water immersion is controlled at 100-300°C, the recovery effect is better. If the temperature of the pressurized water immersion is too high, the element leaching rate will be less improved and the energy utilization rate will be lower.

[0090] By comparing Example 1 with Examples 5-6, it can be seen that in the recovery process described in the present disclosure, the temperature of the pressurized alkali leaching affects the recovery effect. When the temperature of the pressurized alkali leaching is controlled at 150-300°C, the recovery effect is better. If the temperature of the pressurized alkali leaching is too low, the reaction time is long and the Al leaching rate is low. If the temperature of the pressurized alkali leaching is too high, the element leaching rate is not improved much and the energy utilization rate is low.

[0091] By comparing Example 1 with Comparative Example 1, it can be seen that the present disclosure uses a pressurized method, combined with water leaching and alkaline leaching, to achieve the separation of lithium and aluminum, and then obtains refined lithium carbonate, aluminum hydroxide and iron hydroxide precipitates by removing impurities, which can be made into economically profitable products respectively, reducing the cost of recycling waste lithium batteries.

Claims

1. A method for recycling iron-aluminum slag produced in battery recycling in a full-chain integrated manner, the method comprising the following steps: (1) mixing the iron-aluminum slag produced in battery recovery with water, obtaining water-leached slag and water-leached liquid by pressurized water leaching, and washing the water-leached slag with water to obtain a lithium-rich solution; (2) evaporating and concentrating the lithium-rich solution obtained in step (1), and then subjecting it to low-temperature crystallization, and performing solid-liquid separation to obtain sodium sulfate crystals and a lithium precipitation mother liquor, and mixing the lithium precipitation mother liquor with sodium carbonate, and subjecting the solid-liquid separation to obtain lithium carbonate; (3) mixing the water leaching residue after the washing treatment in step (1) with the mother liquor, subjecting the mixture to pressurized alkali leaching, and performing solid-liquid separation to obtain alkali leaching residue and alkali leaching liquid; (4) mixing the alkaline leaching solution with an impurity remover, performing solid-liquid separation to obtain a calcium fluorophosphate impurity precipitate and an impurity-removing liquid, and performing crystallization treatment on the impurity-removing liquid to obtain aluminum hydroxide crystals and a circulating mother liquor; The operation order of step (2) and step (3) is not specific.

2. The method of claim 1, wherein: The solid-liquid mass ratio of the iron-aluminum slag and water in step (1) is 1:(1-5).

3. The method according to claim 1 or 2, wherein: The temperature of the pressurized water immersion is 100-300°C.

4. The method according to any one of claims 1 to 3, wherein: The pressure of the pressurized water immersion is 0.1-8.5 MPa.

5. The method according to any one of claims 1 to 4, wherein: The time of the pressurized water immersion is 0.5 to 3 hours.

6. The method according to any one of claims 1 to 5, wherein: The liquid obtained by the washing treatment in step (1) is mixed with the water immersion liquid to obtain a mixed liquid, and the mixed liquid is used to pressurize the iron-aluminum slag for water immersion again, and the mixture is repeated 3-4 times to obtain a lithium-rich solution.

7. The method according to any one of claims 1 to 6, wherein: The temperature of the low temperature crystallization in step (2) is less than 10°C; Optionally, washing and drying the obtained sodium sulfate crystals; Optionally, the washing detergent comprises water at a temperature < 10°C.

8. The method according to any one of claims 1 to 7, wherein: After the solid-liquid separation in step (2), the lithium carbonate is washed and dried; Optionally, the washing detergent comprises water at a temperature > 60°C.

9. The method according to any one of claims 1 to 8, wherein: The mass ratio of the water-leached residue to the mother liquor in step (3) is (5-12):(20-50); Optionally, the solute of the mother solution includes sodium hydroxide and aluminum hydroxide; Optionally, the caustic ratio of the mother liquor is 2-3.

10. The method according to any one of claims 1 to 9, wherein: The temperature of the pressurized alkali leaching in step (3) is 150-300°C.

11. The method according to any one of claims 1 to 10, wherein: The pressure of the pressurized alkali leaching is 0.1-8.0 MPa.

12. The method according to any one of claims 1 to 11, wherein: The time of the pressurized alkali leaching is 1 to 4 hours.

13. The method according to any one of claims 1 to 12, wherein: After the pressurized alkali leaching, the temperature is lowered to below 100° C., and solid-liquid separation is performed while hot.

14. The method according to any one of claims 1 to 13, wherein: After the solid-liquid separation in step (3), the alkali leaching residue is washed with water, and the obtained washing liquid is mixed with the alkali leaching liquid.

15. The method according to any one of claims 1 to 14, wherein: The impurity remover in step (4) comprises calcium hydroxide; Optionally, the crystallization treatment comprises cold water bath crystallization; Optionally, after the crystallization treatment, the mixture is allowed to stand for 20 to 60 hours before solid-liquid separation treatment.

16. The method according to any one of claims 1 to 15, wherein: The circulating mother liquor in step (4) is used for the pressurized alkali leaching in step (3).

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