A carbon reduction and emission reduction combined recovery method for waste lithium iron phosphate and iron-aluminum slag

Abstract

The present invention provides a carbon reduction and emission reduction combined recovery method for waste lithium iron phosphate and ferroaluminum slag. In the combined recovery method, the ferroaluminum slag is acid-dissolved into an ferroaluminum solution, and the ferroaluminum solution is used as a leaching agent to extract lithium with the waste lithium iron phosphate in two steps without the need for additional acid and oxidant. The first lithium extraction process can achieve efficient and selective leaching of lithium, with a lithium extraction rate of more than 99%, and obtain high-purity ferrophosphate; the second lithium extraction process can convert all trivalent iron in the solution into divalent iron, thereby precipitating aluminum to achieve the purpose of iron-aluminum separation. Subsequently, iron products and valuable metal elements such as nickel, cobalt, and manganese can be further separated to obtain lithium products, thereby achieving lithium extraction to obtain a purified lithium solution.

Description

Technical Field

[0001] The present invention belongs to the field of waste resource recycling and relates to a carbon reduction and emission reduction combined recycling method for waste lithium iron phosphate and iron-aluminum slag. Background Art

[0002] Faced with the severe challenge of global climate change, achieving carbon peak and carbon neutrality have become two strategic goals for driving a green transformation of the economy and society. The new energy industry, particularly those centered around power batteries and energy storage batteries, is rapidly developing on this green wave. By 2023, China's installed power battery capacity exceeded 387.7GWh, with ternary lithium and lithium iron phosphate cathode materials accounting for 32.6% and 67.3% of the market share, respectively. However, with the rapid expansion of the industry, the enormous demand for lithium resources and the increasingly prominent problem of disposing of retired batteries are posing new challenges to the goals of energy conservation, emission reduction, and carbon reduction.

[0003] Therefore, the recycling of used batteries has become a key path to achieving a circular economy and reducing carbon footprints. In terms of the recycling of ternary lithium batteries, given that they contain high-value-added precious metals such as nickel and cobalt and have significant recycling value, the industry has initially established a relatively mature recycling system, which mainly separates iron and aluminum through neutralization and hydrolysis, and enriches nickel and cobalt for recycling. Although this process can effectively recycle some resources, the amount of iron-aluminum slag produced is huge, which in turn causes a large amount of valuable metals to be adsorbed and entrained, resulting in losses. In this regard, the traditional treatment method is to carry out an acid washing process on the iron-aluminum slag to reduce the content of valuable metals in the slag, then solidify it, and then treat the waste slag as general solid waste. However, the disposal methods of acid washing and solidification will cause a large amount of resource waste and increase environmental pollution.

[0004] For example, CN105506290A discloses a method for the comprehensive utilization of iron-aluminum slag, which includes leaching the iron-aluminum slag with sulfuric acid to obtain a leachate containing aluminum sulfate, nickel sulfate and cobalt sulfate, adding sodium sulfide to the leachate, filtering to obtain a mixture containing nickel sulfide and cobalt sulfide, and a crude solution containing aluminum sulfate; after oxidation treatment of the crude solution, sodium hydroxide is added to remove iron, and sodium sulfate is added to obtain a sodium aluminum sulfate stock solution, which is then crystallized to obtain a sodium aluminum sulfate product. However, this process relies on the use of a large amount of sodium sulfide, and will produce harmful hydrogen sulfide gas emissions and increase environmental governance costs, and the obtained nickel sulfide and cobalt sulfide are difficult to further recover to prepare high-value-added organic metal products, which not only leads to high overall recovery costs, but also is not conducive to achieving the "carbon reduction" goal.

[0005] In the recycling of spent lithium iron phosphate batteries, despite their lower valuable metal content compared to ternary lithium batteries, their substantial market share makes recycling equally significant. Currently, oxidative leaching is considered an effective method for selective lithium extraction and recycling of spent lithium iron phosphate materials. This method, without destroying the olivine structure of the lithium iron phosphate crystals, oxidizes the iron in situ, causing it to occupy the lithium lattice, thereby enabling the selective extraction of lithium. However, this process relies on the use of strong oxidants such as hydrogen peroxide, sodium persulfate, or sodium hypochlorite, and must be operated in a high-temperature, highly acidic environment. This not only consumes significant energy but can also pose serious environmental pollution and safety risks.

[0006] In summary, current recycling technologies for spent lithium iron phosphate batteries and ferro-aluminum slag generally suffer from high energy consumption, severe pollution, and high costs, seriously hindering the greener and more sustainable development of the new energy industry chain. Therefore, there is an urgent need to develop innovative energy-saving, carbon-reduction, and emission-reduction solutions to achieve efficient and selective lithium extraction from spent lithium iron phosphate batteries and high-value recycling of ferro-aluminum slag, thereby helping the new energy industry to continuously move towards a greener and lower-carbon development path while ensuring resource recycling. Summary of the Invention

[0007] In view of the problems existing in the prior art, the purpose of the present invention is to provide a carbon reduction and emission reduction combined recovery method for waste lithium iron phosphate and ferroaluminum slag. The combined recovery method dissolves the ferroaluminum slag into an iron-aluminum solution with acid, and uses the iron-aluminum solution to perform two lithium extraction processes on the waste lithium iron phosphate, thereby separating and recovering iron, aluminum, lithium and valuable metal resources.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a carbon reduction and emission reduction combined recovery method for waste lithium iron phosphate and iron-aluminum slag, comprising:

[0010] S1. The iron-aluminum slag is acid-dissolved to obtain an iron-aluminum solution;

[0011] S2. The iron-aluminum solution is mixed with a portion of waste lithium iron phosphate, and a lithium extraction is performed to extract all the lithium to obtain a lithium extraction solution and iron phosphate slag;

[0012] S3. The primary lithium extraction solution is mixed with another portion of waste lithium iron phosphate, and a secondary lithium extraction is performed to partially leach the lithium element to obtain a secondary lithium extraction solution and a secondary lithium extraction slag;

[0013] S4. The secondary lithium extraction solution is subjected to aluminum removal to obtain an aluminum product and an aluminum removal liquid;

[0014] S5. The aluminum removal liquid is subjected to iron removal to obtain an iron product and an iron removal liquid;

[0015] S6. Deeply remove impurities from the iron removal liquid to obtain valuable metal slag and lithium solution.

[0016] The combined recovery method of the present invention directly dissolves the iron-aluminum slag in acid to obtain an iron-aluminum solution (containing trivalent iron), and uses the iron-aluminum solution as a leaching agent to completely react the insufficient amount (less than the theoretical reaction amount) of waste lithium iron phosphate to perform a lithium extraction (the reaction mechanism includes LiFePO4+Fe 3+ =Fe 2+ +Li + +FePO4), so that all the lithium elements in this part of the waste lithium iron phosphate are leached out, and iron phosphate slag is obtained to ensure a high leaching rate of lithium elements and high purity of iron phosphate in the obtained iron phosphate slag. After the first lithium extraction is completed, the iron-aluminum solution still contains a large amount of unreacted trivalent iron ions and remains in the acidic primary lithium extraction solution. Therefore, the present invention reuses the primary lithium extraction solution to react with an excess (greater than the theoretical reaction amount) of waste lithium iron phosphate to perform secondary lithium extraction (the reaction mechanism is the same as the primary lithium extraction), so that only a portion of the lithium iron phosphate is reacted (i.e., a portion of the lithium element is leached), thereby ensuring that all trivalent iron in the solution is consumed and converted into divalent iron to be retained in the secondary lithium extraction solution. Subsequently, the secondary lithium extraction liquid can be used to remove aluminum to obtain aluminum products, so that aluminum elements are separated from iron elements; after the aluminum removal liquid is de-ironized, the resulting de-iron removal liquid contains lithium elements and valuable metal elements such as nickel and cobalt. After further deep removal of the valuable metal elements, a purified lithium solution can be obtained; the lithium solution can be directly used as a lithium precipitation mother liquor to prepare battery-grade lithium carbonate, so that the lithium element can be recycled. The combined recovery method does not require pickling and solidification of the iron-aluminum slag and can be directly used for the combined recovery and treatment of waste lithium iron phosphate. The reaction process of the two lithium extraction steps does not require the use of additional oxidants and does not require a high-temperature environment, and can be carried out at room temperature. The single lithium extraction of the combined recovery method can make the selective lithium extraction rate of waste lithium iron phosphate reach more than 99%, and phosphorus is not leached to obtain a high-purity iron phosphate product, and aluminum products and iron products can be obtained and valuable metals such as nickel and cobalt can be recovered, realizing the full and high-value recovery and utilization of each element in waste lithium iron phosphate and iron-aluminum slag. The combined recovery method has a short process, simple equipment requirements, and is easy to operate. It is an ideal large-scale industrial solution that is conducive to achieving energy conservation, carbon reduction, and emission reduction.

[0017] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0018] As a preferred technical solution of the present invention, the secondary lithium extraction slag in step S3 is recycled and used for the primary lithium extraction in step S2.

[0019] The secondary lithium extraction slag in the present invention contains unreacted lithium iron phosphate, so it can be reused in the primary lithium extraction.

[0020] As a preferred technical solution of the present invention, the iron removal liquid in step S5 is recycled and used for the acid dissolution in step S1 to increase the lithium concentration of the obtained iron removal liquid.

[0021] In the present invention, the iron removal liquid is an acidic solution containing valuable metal ions and lithium ions, and can therefore be reused in the acid dissolution process of step S1. Furthermore, it can be used as a base liquid for slurrying of iron and aluminum slag, and then mixed with an acid solution for acid dissolution. By repeatedly circulating the iron removal liquid, its lithium concentration can be increased until the target requirement is reached, and it can enter the deep impurity removal process, that is, the concentration and enrichment of lithium is achieved in the method of the invention, and the resulting lithium solution does not require additional evaporation and concentration treatment, and can be directly used as a lithium precipitation mother liquor to obtain a battery-grade lithium carbonate product.

[0022] As a preferred technical solution of the present invention, the iron-aluminum slag described in step S1 includes iron-aluminum slag recovered from waste ternary and / or quaternary battery powder; the waste lithium iron phosphate described in steps S2 and S3 is electrode powder.

[0023] Preferably, before the acid dissolution, the iron-aluminum slag is first slurried according to a solid-liquid ratio of 1g:(1-3)mL, and then the acid dissolution is performed, for example, 1g:1mL, 1g:1.3mL, 1g:1.5mL, 1g:1.8mL, 1g:2mL, 1g:2.2mL, 1g:2.5mL, 1g:2.8mL or 1g:3mL, etc.

[0024] Preferably, the acid solution used in the acid dissolution includes sulfuric acid and / or hydrochloric acid.

[0025] Preferably, the amount of the acid solution is controlled according to the pH value of the acid solution being 1.0 to 1.5, for example, 1, 1.1, 1.2, 1.3, 1.4 or 1.5.

[0026] As a preferred technical solution of the present invention, in step S2, the amount of the waste lithium iron phosphate is controlled according to 50% to 80% of the theoretical reaction amount with the iron-aluminum solution, for example, 50%, 53%, 55%, 58%, 60%, 63%, 65%, 68%, 71%, 74%, 77% or 80%, etc., that is, the amount of the waste lithium iron phosphate is controlled to be insufficient.

[0027] Preferably, the temperature of the primary lithium extraction is 15-30°C, for example, 15°C, 18°C, 21°C, 24°C, 27°C or 30°C, and the time is 20-60 min, for example, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min.

[0028] As a preferred technical solution of the present invention, in step S3, the amount of the waste lithium iron phosphate is controlled according to 100.1% to 200% of the theoretical reaction amount of the primary lithium extraction solution, for example, 100.1%, 110%, 120%, 130%, 140%, 150%, 160%, 170%, 180%, 190% or 200%.

[0029] Preferably, the temperature of the secondary lithium extraction is 15-30°C, for example, 15°C, 18°C, 21°C, 24°C, 27°C or 30°C, and the time is 20-60min, for example, 20min, 25min, 30min, 35min, 40min, 45min, 50min, 55min or 60min.

[0030] In the present invention, both the primary and secondary lithium extraction processes can be performed at room temperature without the need for high-temperature heating or additional acid addition. Depending on the acid used to dissolve the ferroaluminum slag, the following reaction mechanism can be employed: when the acid solution used includes sulfuric acid, the reaction process between the waste lithium iron phosphate and the ferroaluminum solution comprises 2LiFePO4 + Fe2(SO4)3 = 2FeSO4 + Li2SO4 + 2FePO4; when the acid solution used includes hydrochloric acid, the reaction process between the waste lithium iron phosphate and the ferroaluminum solution comprises LiFePO4 + FeCl3 = FeCl2 + LiCl + FePO4.

[0031] As a preferred technical solution of the present invention, the aluminum removal method includes heating the secondary lithium extraction solution to 60-90°C, for example, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C or 90°C, adding an alkaline regulator, adjusting the pH to 4.4-4.8, for example, 4.4, 4.5, 4.6, 4.7 or 4.8, and performing a first precipitation reaction for 0.5-1h, for example, 0.5h, 0.6h, 0.7h, 0.8h, 0.9h or 1h, to obtain an aluminum product and an aluminum removal liquid.

[0032] As a preferred technical solution of the present invention, the method for removing iron includes heating the aluminum removal liquid to 40-90°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C or 90°C, adding an alkaline regulator, adjusting the pH to 4.8-5.4, for example, 4.8, 4.9, 5, 5.1, 5.2, 5.3 or 5.4, and introducing an oxygen-containing gas for a second precipitation reaction for 3-6 hours, for example, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours or 6 hours, to obtain an iron product and an iron removal liquid.

[0033] During iron precipitation, nickel, cobalt and other metals are simultaneously precipitated in the iron product due to local over-alkalinity. Valuable metals can be dissolved back through acid washing to obtain a purer iron product.

[0034] As a preferred technical solution of the present invention, the deep impurity removal method includes heating the iron removal liquid to 40-80°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, adding an alkaline regulator, adjusting the pH to 10-12, for example, 10, 10.2, 10.4, 10.6, 10.8, 11, 11.2, 11.4, 11.6, 11.8 or 12, and conducting a third precipitation reaction for 0.5-2h, for example, 0.5h, 0.8h, 1h, 1.2h, 1.4h, 1.6h, 1.8h or 2h, to obtain valuable metal slag and lithium solution.

[0035] As a preferred technical solution of the present invention, the alkaline regulator includes soda ash and / or liquid caustic soda; the aluminum product includes natantrol aluminum vanadium; the iron product includes goethite; and the valuable metal slag contains nickel and / or cobalt.

[0036] In the present invention, when the acid solution for acid dissolving the ferroaluminum slag includes sulfuric acid and the alkaline regulator used contains sodium, the obtained aluminum product includes yellow sodium aluminum vanadium (the sodium element comes from the alkaline regulator). The reaction of the yellow sodium aluminum vanadium generation process may include: 3Al2(SO4)3+Na2SO4+12H2O→Na2Al6(SO4)4(OH) 12 ↓+

[0037] 6H2SO4 and H2SO4 + Na2CO3 → Na2SO4 + H2O + 3CO2↑. When the aluminum product is preferably yellow sodium aluminum vanadium, it has good molding, high solid-liquid separation efficiency, low valuable metal carryover, and can be washed and then slaged. Compared with the existing process of pickling and solidifying the iron-aluminum slag, this helps avoid the additional cost caused by aluminum re-dissolution during the pickling of the iron-aluminum slag. The goethite slag obtained by the present invention is small in volume and insoluble in acid.

[0038] Compared with the existing technical solutions, the present invention has at least the following beneficial effects:

[0039] The present invention utilizes an acid-soluble solution of ferroaluminum slag as a leaching agent, and extracts lithium from waste lithium iron phosphate in two steps without the need for additional acid and oxidant. The first lithium extraction step can achieve efficient and selective leaching of lithium, with a lithium extraction rate of more than 99%, and obtain a high-purity ferric phosphate product; the second lithium extraction step can convert all trivalent iron in the solution into divalent iron, thereby precipitating aluminum to achieve the purpose of iron-aluminum separation, and subsequently further separation can be performed to obtain iron products and valuable metal elements such as nickel, cobalt, and manganese, thereby achieving lithium extraction to obtain a purified lithium solution.

[0040] The present invention does not perform the existing process of pickling and solidifying the iron-aluminum slag, thereby avoiding the cost increase caused by the re-dissolution of iron and aluminum during pickling. The iron-aluminum slag in the present invention is finally recycled in the form of aluminum products such as natantrite and iron products such as goethite, which can not only realize the separation and resource utilization of iron and aluminum, but also effectively recover valuable metals to significantly reduce their loss rate.

[0041] The present invention avoids the strong oxidation and high-temperature and high-acid reaction conditions imposed on waste lithium iron phosphate by the prior art for lithium extraction, which is beneficial for saving resources and processes and avoiding the cost increase caused by pollution or waste treatment.

[0042] The present invention improves the lithium concentration of the obtained iron removal liquid and lithium solution by adjusting the liquid-to-solid ratio of the iron-aluminum slag acid dissolution process or recycling the iron removal liquid back to the acid dissolution process, so that the obtained lithium solution does not need to be evaporated and concentrated, and can be directly used as a lithium precipitation mother liquor for preparing lithium products.

[0043] The present invention achieves full and high-value recycling of various elements in waste lithium iron phosphate and iron-aluminum slag with a short process, simple equipment requirements and easy operation. It is an ideal large-scale industrial solution that is conducive to achieving energy conservation, carbon reduction and emission reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a flow chart of a carbon reduction and emission reduction combined recovery method for waste lithium iron phosphate and iron-aluminum slag in Example 1.

[0045] Figure 2 The XRD test curves of the waste lithium iron phosphate electrode powder (curve (a)) and the obtained iron phosphate slag (curve (b)) in Example 1 and the XRD test curve of the iron phosphate slag (curve (c)) obtained in Example 2;

[0046] Figure 3 This is an XRD test curve of the aluminum product yellow sodium aluminum vanadium obtained in Example 1;

[0047] Figure 4 This is an XRD test curve of the iron product goethite obtained in Example 1; DETAILED DESCRIPTION

[0048] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0049] It should be apparent to those skilled in the art that the embodiments are only intended to help understand the present invention and should not be considered as specific limitations of the present invention.

[0050] Example 1

[0051] This embodiment provides a carbon reduction and emission reduction combined recovery method for waste lithium iron phosphate and iron aluminum slag, such as Figure 1 Shown, including:

[0052] S1. Acid dissolution: The iron-aluminum slag recovered from the waste ternary battery powder (ternary nickel-cobalt-manganese) was slurried with water at a solid-liquid ratio of 1g:1mL, and then sulfuric acid was added to adjust the pH to 1.0-1.5 to completely dissolve the iron-aluminum slag to obtain an iron-aluminum solution (containing iron sulfate and aluminum sulfate);

[0053] S2. Primary lithium extraction: 50% of the theoretical reaction amount of waste lithium iron phosphate electrode powder with the iron-aluminum solution was added to the iron-aluminum solution and stirred at room temperature of 25°C for 20 minutes to perform a primary lithium extraction to completely leach the lithium element. The solid-liquid separation was then performed to obtain a primary lithium extraction solution and iron phosphate slag; the obtained iron phosphate slag was washed with countercurrent water three times and then discharged;

[0054] The mass percentages of the main elements in the waste lithium iron phosphate electrode powder used are shown in Table 1:

[0055] Table 1

[0056] iron lithium nickel cobalt manganese copper aluminum phosphorus 30.23％ 4.14％ 0.20％ 0.01％ 0.01％ 0.01％ 0.05％ 18.62％

[0057] S3. Secondary lithium extraction: 150% of the theoretical reaction amount of the waste lithium iron phosphate electrode powder with the primary lithium extraction solution was added to the primary lithium extraction solution, stirred at room temperature at 25°C for 60 minutes, and secondary lithium extraction was performed to partially leach the lithium element and convert all the trivalent iron ions in the solution into divalent iron ions. The solid-liquid separation was then performed to obtain a secondary lithium extraction solution and a secondary lithium extraction slag; the obtained secondary lithium extraction slag was returned to the primary lithium extraction process in step S2;

[0058] S4. Aluminum removal: The secondary lithium extraction solution was heated to 90 ° C, a 10% soda ash solution was added, the addition rate was controlled, and the reaction was stirred until the pH value of the solution stabilized to 4.4. The first precipitation reaction was carried out, and the solid-liquid separation was continued after stirring for 1 hour to obtain an aluminum removal liquid and an aluminum product, naoite; the naoite was washed with water and the slag was removed;

[0059] S5. Iron removal: The dealuminization solution was adjusted to a pH of 4.8 to 5.1 with soda ash, and air was introduced from the bottom of the dealuminization solution using an ozone generator to oxidize the iron element. The reaction temperature was controlled at 40°C, and a second precipitation reaction was carried out for 4 hours. After titration to detect that all ferrous iron was oxidized, stirring was continued for 30 minutes, and then solid-liquid separation was performed to obtain a dealuminization solution and an iron product, goethite; the goethite was first acid-washed and then washed with water before slagging;

[0060] S6. Deep impurity removal: Heat the iron removal solution to 70°C, add liquid alkali to adjust the pH to 11, stir and react for 1 hour, and carry out the third precipitation reaction. After solid-liquid separation, valuable metal slag nickel and cobalt slag and purified lithium solution (containing lithium sulfate) are obtained.

[0061] Example 2

[0062] This embodiment provides a carbon reduction and emission reduction combined recovery method for waste lithium iron phosphate and iron-aluminum slag, comprising:

[0063] S1. Acid dissolution: The iron-aluminum slag obtained by recovering the waste ternary battery powder (the same as in Example 1) was slurried with water at a solid-liquid ratio of 1g: 3mL and stirred, and then hydrochloric acid was added to adjust the pH to 1.0-1.5, so that the iron-aluminum slag was completely dissolved to obtain an iron-aluminum solution (containing ferric chloride and aluminum chloride);

[0064] S2. Primary lithium extraction: 80% of the theoretical reaction amount of waste lithium iron phosphate electrode powder (the same as in Example 1) was added to the iron-aluminum solution and stirred at room temperature of 25°C for 40 minutes to perform a primary lithium extraction to completely leach the lithium element. The solid-liquid separation was then performed to obtain a primary lithium extraction solution and iron phosphate slag; the obtained iron phosphate slag was washed with countercurrent water three times and then discharged;

[0065] S3. Secondary lithium extraction: 120% of the theoretical reaction amount of the waste lithium iron phosphate electrode powder with the primary lithium extraction solution was added to the primary lithium extraction solution, stirred at room temperature at 25°C for 30 minutes, and secondary lithium extraction was performed to partially leach the lithium element and convert all the trivalent iron ions in the solution into divalent iron ions. The solid-liquid separation was then performed to obtain a secondary lithium extraction solution and a secondary lithium extraction slag; the obtained secondary lithium extraction slag was returned to the primary lithium extraction process in step S2;

[0066] S4. Aluminum removal: The secondary lithium extraction solution was heated to 60 ° C, a 15% mass percentage concentration of soda ash solution was added, the addition rate was controlled, and the reaction was stirred until the pH value of the solution stabilized to 4.6. The first precipitation reaction was carried out, and the solid-liquid separation was continued after stirring for 0.5h to obtain aluminum removal liquid and aluminum product aluminum hydroxide; the aluminum hydroxide was washed with water and the slag was removed;

[0067] S5. Iron removal: The de-aluminum solution was adjusted to a pH value within the range of 5.1 to 5.4 with soda ash, and air was introduced from the bottom of the de-aluminum solution using an ozone generator to oxidize the iron element. The reaction temperature was controlled at 60°C for a second precipitation reaction of 5 hours. After titration, the ferrous iron was completely oxidized, and stirring was continued for 30 minutes. The solid-liquid separation was then performed to obtain a de-aluminum solution and an iron product, goethite. The goethite was first acid-washed and then washed with water before slagging. The de-aluminum solution was recycled and used as a base liquid for slurrying in step S1 until the lithium concentration in the de-aluminum solution obtained in step S5 reached the target, and then step S6 was performed.

[0068] S6. Deep impurity removal: Heat the iron removal solution to 40°C, add liquid alkali to adjust the pH to 12, stir and react for 1 hour, and perform a third precipitation reaction. After solid-liquid separation, valuable metal slag nickel and cobalt slag and purified lithium solution (containing lithium chloride) are obtained.

[0069] Example 3

[0070] This embodiment provides a carbon reduction and emission reduction combined recovery method for waste lithium iron phosphate and iron-aluminum slag, comprising:

[0071] S1. Acid dissolution: The waste ternary battery powder (the same as in Example 1) was recovered and the obtained iron-aluminum slag was slurried and stirred with water at a solid-liquid ratio of 1g: 2mL, and then sulfuric acid was added to adjust the pH to 1.0-1.5, so that the iron-aluminum slag was completely dissolved to obtain an iron-aluminum solution (containing iron sulfate and aluminum sulfate);

[0072] S2. Primary lithium extraction: 60% of the theoretical reaction amount of waste lithium iron phosphate electrode powder (the same as in Example 1) was added to the iron-aluminum solution and stirred at room temperature of 25°C for 20 minutes to perform a primary lithium extraction to completely leach the lithium element. The solid-liquid separation was then performed to obtain a primary lithium extraction solution and iron phosphate slag; the obtained iron phosphate slag was washed with countercurrent water three times and then discharged;

[0073] S3. Secondary lithium extraction: 120% of the theoretical reaction amount of the waste lithium iron phosphate electrode powder with the primary lithium extraction solution was added to the primary lithium extraction solution, stirred at room temperature at 25°C for 30 minutes, and secondary lithium extraction was performed to partially leach the lithium element and convert all the trivalent iron ions in the solution into divalent iron ions. The solid-liquid separation was then performed to obtain a secondary lithium extraction solution and a secondary lithium extraction slag; the obtained secondary lithium extraction slag was returned to the primary lithium extraction process in step S2;

[0074] S4. Aluminum removal: The secondary lithium extraction solution was heated to 80 ° C, a 20% mass percentage concentration of soda ash solution was added, the addition rate was controlled, and the reaction was stirred until the pH value of the solution stabilized to 4.6. The first precipitation reaction was carried out and the solid-liquid separation was continued after stirring for 0.5h to obtain an aluminum removal liquid and an aluminum product, yellow sodium aluminum vanadium; the yellow sodium aluminum vanadium was washed and the slag was removed;

[0075] S5. Iron removal: The de-aluminum solution was adjusted to a pH value within the range of 5.1 to 5.4 with soda ash, and air was introduced from the bottom of the de-aluminum solution using an ozone generator to oxidize the iron element. The reaction temperature was controlled at 90°C for a second precipitation reaction of 3 hours. After titration, the ferrous iron was completely oxidized, and stirring was continued for 30 minutes. The solid-liquid separation was then performed to obtain a de-aluminum solution and an iron product, goethite; the goethite was first acid-washed and then washed with water before slagging; the de-aluminum solution was recycled and used as a base liquid for slurrying in step S1 until the lithium concentration in the de-aluminum solution obtained in step S5 reached the target, and then step S6 was performed.

[0076] S6. Deep impurity removal: Heat the iron removal solution to 80°C, add liquid alkali to adjust the pH to 12, stir and react for 1 hour, and carry out the third precipitation reaction. After solid-liquid separation, valuable metal slag nickel and cobalt slag and purified lithium solution (containing lithium sulfate) are obtained.

[0077] Example 4

[0078] This embodiment provides a carbon reduction and emission reduction combined recovery method for waste lithium iron phosphate and iron-aluminum slag. In step S2, the combined recovery method adjusts the amount of waste lithium iron phosphate electrode powder from 50% to 90% of the theoretical reaction amount with the iron-aluminum solution. Except for the above, other conditions are exactly the same as those in Example 1.

[0079] Example 5

[0080] This embodiment provides a carbon reduction and emission reduction combined recovery method for waste lithium iron phosphate and iron-aluminum slag. In step S3, the combined recovery method adjusts the amount of waste lithium iron phosphate electrode powder from 150% of the theoretical reaction amount with the primary lithium extraction solution to 101%. Except for the above, other conditions are exactly the same as those in Example 1.

[0081] Example 6

[0082] This embodiment provides a carbon reduction and emission reduction combined recovery method for waste lithium iron phosphate and iron-aluminum slag. In step S3, the combined recovery method adjusts the amount of waste lithium iron phosphate electrode powder from 150% to 210% of the theoretical reaction amount with the primary lithium extraction solution. Except for the above, other conditions are exactly the same as those in Example 1.

[0083] Example 7

[0084] This embodiment provides a carbon reduction and emission reduction combined recovery method for waste lithium iron phosphate and iron-aluminum slag. The combined recovery method adjusts the waste lithium iron phosphate electrode powder to waste lithium iron manganese phosphate electrode powder. Except for the above, other conditions are exactly the same as those in Example 1.

[0085] Comparative Example 1

[0086] This comparative example provides a combined recovery method for waste lithium iron phosphate and iron-aluminum slag. The combined recovery method only performs one lithium extraction, that is, step S3 is not performed, and the one-time lithium extraction liquid obtained in step S2 is used in step S4. Except for the above, other conditions are exactly the same as those in Example 1.

[0087] Comparative Example 2

[0088] This comparative example provides a combined recovery method for waste lithium iron phosphate and iron-aluminum slag. The combined recovery method only performs one lithium extraction, and in step S2, the amount of waste lithium iron phosphate electrode powder is adjusted from 50% of the theoretical reaction amount with the iron-aluminum solution to 100%, and step S3 is not performed. The one-time lithium extraction solution obtained in step S2 is used in step S4. Except for the above, other conditions are exactly the same as those in Example 1.

[0089] Characterization and testing:

[0090] Ⅰ. Figure 2It is the XRD test curve diagram of the waste lithium iron phosphate electrode powder (curve (a)) and the obtained iron phosphate slag (curve (b)) in Example 1, as well as the XRD test curve diagram of the iron phosphate slag (curve (c)) obtained in Example 2; it can be seen from the figure that the raw material of the waste lithium iron phosphate electrode powder is LiFePO4 with an orthorhombic olivine structure, and the XRD spectrum of the obtained leached slag is similar to that of the raw material, both of which are well-crystallized orthorhombic FePO4 phases.

[0091] The dry elemental composition in the iron phosphate slag obtained in the embodiment and the comparative example was detected, and the Li leaching rate was calculated as 100% - the mass of Li in the iron phosphate slag / the mass of Li in the waste lithium iron phosphate electrode powder. The P leaching rate was calculated as the mass of P in the primary lithium extraction solution / the mass of P in the waste lithium iron phosphate electrode powder. The results are shown in Table 2.

[0092] Table 2

[0093]

[0094]

[0095] As can be seen from Table 1, in Examples 1, 2, 3, 5, 6, 7, and Comparative Example 1, in step S2, the amount of waste lithium iron phosphate was controlled to 50% to 80% of the theoretical reaction amount with the iron-aluminum solution. The resulting iron phosphate slag, after selective lithium extraction, contained less than 0.05% lithium and low levels of other impurity metals. The resulting iron phosphate slag can be used to prepare new LiFePO4 positive electrode materials. The selective lithium extraction rate using the iron-aluminum slag acid solution was greater than 99%.

[0096] Ⅱ. Figure 3 This is an XRD test curve of the aluminum product yellow sodium aluminum vanadium obtained in Example 1. It can be seen from the figure that the obtained yellow sodium aluminum alum slag has good crystallinity and large grains, which is conducive to solid-liquid separation and has low metal entrainment.

[0097] The dry elemental compositions of the aluminum products obtained in the examples and comparative examples were tested, and the results are shown in Table 3.

[0098] Table 3

[0099]

[0100] As can be seen from Table 3, the total nickel and cobalt content in the aluminum product derived from the iron-aluminum solution in the embodiment is less than 0.5% (the nickel and cobalt content in the original iron-aluminum slag is 4% to 10%). The main reason is that the nickel and cobalt concentration in the iron-aluminum solution system after acid dissolution is much lower than the nickel and cobalt concentration in the original ternary system when removing iron and aluminum. At this time, by adjusting and controlling the pH, the probability of valuable metals such as nickel and cobalt being precipitated is further reduced. Furthermore, when the obtained aluminum product is yellow sodium aluminum alum, the adsorption rate of nickel and cobalt is lower than that of aluminum hydroxide. The yellow sodium aluminum alum slag can be washed with water to remove the entrained metals without acid washing. Because Example 5 and Comparative Examples 1-2 contain a small amount of trivalent iron, the trivalent iron is precipitated together when the aluminum is precipitated. Therefore, the aluminum content in the obtained aluminum slag is reduced, which is not conducive to the resource utilization of the slag.

[0101] III. Figure 4 This is an XRD test curve of the iron product goethite obtained in Example 1. As can be seen from the figure, the iron slag obtained is goethite. Goethite is difficult to dissolve in acid, so relatively pure goethite can be obtained by acid washing.

[0102] The dry element composition of the iron products obtained in the examples and comparative examples was tested, and the results are shown in Table 4:

[0103] Table 4

[0104]

[0105] As can be seen from Table 4, after the iron products obtained in the Examples and Comparative Examples were pickled and washed, the iron content in the slag was as high as 55%, and the nickel and cobalt content was less than 0.2%. The amount of slag obtained by the goethite method was small, the iron did not dissolve back during pickling, the slag metal content was low, and the loss rate of valuable metals was reduced.

[0106] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0107] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0108] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A carbon reduction and emission reduction combined recovery method for waste lithium iron phosphate and iron-aluminum slag, characterized in that: include: S1. The iron and aluminum slag is acid-dissolved to obtain an iron and aluminum solution; S2. The iron-aluminum solution is mixed with a portion of waste lithium iron phosphate, and a lithium extraction is performed to extract all the lithium to obtain a lithium extraction solution and iron phosphate slag; S3. The primary lithium extraction solution is mixed with another portion of waste lithium iron phosphate, and a secondary lithium extraction is performed to partially leach the lithium element to obtain a secondary lithium extraction solution and a secondary lithium extraction slag; S4 the secondary lithium extraction solution is subjected to aluminum removal to obtain an aluminum product and aluminum removal liquid; S5. The aluminum removal liquid is subjected to iron removal to obtain an iron product and an iron removal liquid; S6. Deeply removing impurities from the iron removal solution to obtain valuable metal slag and lithium solution.

2. The carbon reduction and emission reduction combined recovery method of waste lithium iron phosphate and iron-aluminum slag according to claim 1, characterized in that: The secondary lithium extraction slag in step S3 is recycled and used for the primary lithium extraction in step S2.

3. The carbon reduction and emission reduction combined recovery method of waste lithium iron phosphate and iron-aluminum slag according to claim 1, characterized in that: The iron removal solution in step S5 is recycled and used for the acid dissolution in step S1 to increase the lithium concentration of the obtained iron removal solution.

4. The carbon reduction and emission reduction combined recovery method of waste lithium iron phosphate and iron-aluminum slag according to claim 1, characterized in that: The iron-aluminum slag described in step S1 includes the iron-aluminum slag recovered from waste ternary and / or quaternary battery powder.

5. The carbon reduction and emission reduction combined recovery method of waste lithium iron phosphate and iron-aluminum slag according to claim 1, characterized in that: Before the acid dissolution, the iron-aluminum slag is first slurried according to a solid-liquid ratio of 1 g: (1-3) mL, and then the acid dissolution is performed.

6. The carbon reduction and emission reduction combined recovery method of waste lithium iron phosphate and iron-aluminum slag according to claim 1, characterized in that: The acid solution used in the acid dissolution includes sulfuric acid and / or hydrochloric acid.

7. The carbon reduction and emission reduction combined recovery method of waste lithium iron phosphate and iron-aluminum slag according to claim 6, characterized in that: The amount of the acid solution is controlled according to the pH value of the acid solution being 1.0 to 1.

5.

8. The carbon reduction and emission reduction combined recovery method of waste lithium iron phosphate and iron-aluminum slag according to claim 1, characterized in that: In step S2, the amount of the waste lithium iron phosphate is controlled to be 50% to 80% of the theoretical reaction amount with the iron-aluminum solution.

9. The carbon reduction and emission reduction combined recovery method of waste lithium iron phosphate and iron-aluminum slag according to claim 1, characterized in that: The temperature of the primary lithium extraction is 15-30° C., and the time is 20-60 min.

10. The carbon reduction and emission reduction combined recovery method of waste lithium iron phosphate and iron-aluminum slag according to claim 1, characterized in that: In step S3, the amount of the waste lithium iron phosphate is controlled according to 100.1% to 200% of the theoretical reaction amount of the primary lithium extraction solution.

11. The carbon reduction and emission reduction combined recovery method of waste lithium iron phosphate and iron-aluminum slag according to claim 1, characterized in that: The temperature of the secondary lithium extraction is 15-30° C., and the time is 20-60 min.

12. The carbon reduction and emission reduction combined recovery method of waste lithium iron phosphate and iron-aluminum slag according to claim 1, characterized in that: The aluminum removal method includes heating the secondary lithium extraction solution to 60-90° C., adding an alkaline regulator, adjusting the pH to 4.4-4.8, and performing a first precipitation reaction for 0.5-1 hour to obtain an aluminum product and an aluminum removal solution.

13. The carbon reduction and emission reduction combined recovery method of waste lithium iron phosphate and iron-aluminum slag according to claim 1, characterized in that: The iron removal method includes heating the aluminum removal liquid to 40-90° C., adding an alkaline regulator, adjusting the pH to 4.8-5.4, and introducing an oxygen-containing gas to perform a second precipitation reaction for 3-6 hours to obtain an iron product and an iron removal liquid.

14. The carbon reduction and emission reduction combined recovery method of waste lithium iron phosphate and iron-aluminum slag according to claim 1, characterized in that: The deep impurity removal method includes heating the iron removal liquid to 40-80° C., adding an alkaline regulator, adjusting the pH to 10-12, and performing a third precipitation reaction for 0.5-2 hours to obtain valuable metal slag and a lithium solution.

15. The carbon reduction and emission reduction combined recovery method of waste lithium iron phosphate and iron-aluminum slag according to any one of claims 12 to 14, characterized in that: The alkaline regulator includes soda ash and / or liquid caustic soda; the aluminum product includes natantrol; the iron product includes goethite; and the valuable metal slag contains nickel and / or cobalt.

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