Method for improving lithium recovery rate in aluminum electrolysis lithium-containing waste residue

Abstract

The application discloses a method for improving lithium recovery rate in aluminum electrolysis lithium-containing waste residue, and belongs to the technical field of solid waste resource recovery. Part of waste electrolyte, anode carbon residue and overhaul residue generated in aluminum electrolysis contain fluorine aluminum compounds and a small amount of lithium elements. After acid liquid leaching, lithium and part of fluorine aluminum components are transferred into liquid phase to form lithium-containing liquid with recovery value. The acid leaching liquid needs to be purified by adding alkali before lithium precipitation. Fluorine aluminum complex ions are easy to hydrolyze and generate hydroxyl aluminum fluoride colloid precipitate with fine particle size and negative surface during the process. The precipitate is easy to adsorb Li⁺, leading to loss of lithium with filter residue. In view of the above problems, a cationic interfacial modifier is introduced in the process of adding alkali. The cationic group in the cationic interfacial modifier is preferentially adsorbed on the negative potential points on the surface of the colloid particles, weakening the adsorption of the colloid particles on Li⁺. The cationic interfacial modifier promotes flocculation and aggregation of the colloid particles, particle size growth, reduction of filter residue entraining lithium-containing mother liquor, improvement of lithium retention rate in the purified liquid, and preparation of lithium salt products.

Description

[0001] This invention belongs to the technical fields of lithium-containing leachate purification of aluminum electrolysis waste residue, resource utilization of aluminum electrolysis solid waste and lithium resource recovery, and specifically relates to a method for improving the lithium recovery rate in lithium-containing aluminum electrolysis waste residue. Background Technology

[0002] my country has long been the world's largest producer of primary aluminum, accounting for over 60% of global output. However, my country's bauxite resources are relatively low-grade, and in some mining areas, aluminum and lithium coexist, resulting in alumina raw materials with relatively high lithium oxide content. This lithium salt, after entering the molten salt of the aluminum electrolyte along with the alumina, gradually accumulates in the electrolytic cell and needs to be periodically removed, generating lithium-containing solid waste such as waste aluminum electrolyte, anode carbon slag, and overhaul slag. This type of solid waste contains high-value lithium and fluorine resources, making its resource utilization significant.

[0003] Existing lithium recovery processes from lithium-containing solid waste from aluminum electrolysis typically involve steps such as inorganic acid leaching, alkali conversion-acid leaching, organic acid leaching, or roasting-water leaching. These processes introduce lithium from the solid waste into the liquid phase, yielding a lithium-containing leachate. Further purification, evaporation and concentration, and lithium salt precipitation are then performed to ultimately obtain the lithium salt product. In addition to Li⁺, the lithium-containing leachate usually also contains Al. 3+ Al-F complex ion (AlF2) + AlF 2+ AlF4 - AlF5 2- etc.), free F - Na + Ca 2+ Plasma. Before preparing lithium salts by lithium precipitation, elements such as Al and F are usually removed by adding alkali. With the addition of an alkaline regulator, aluminum-fluorine complex ions undergo hydrolysis, hydroxyl substitution, polymerization, and co-precipitation reactions to form hydroxylated aluminum fluoride colloidal precipitate, the composition of which can be represented as AlF x (OH) 3-x ·nH2O. This type of precipitate typically has characteristics such as low crystallinity, high hydration, fine particle size, large specific surface area, slow sedimentation, and difficulty in filtration.

[0004] More importantly, the surface of hydroxyl aluminum fluoride colloidal particles is rich in hydroxyl sites (≡Al–OH) and fluorine coordinating groups (≡Al–F). As the pH of the system increases, the hydroxyl groups on the colloidal surface readily undergo deprotonation, forming negatively charged ≡Al–O⁻ sites. Simultaneously, adsorbed F⁻ and OH⁻ exist at the particle interface, collectively enhancing the negative charge of the colloidal precipitate surface and increasing its absolute Zeta potential. The negative charge of the hydroxyl aluminum fluoride colloidal precipitate surface affects the distribution behavior of lithium ions. Since Li⁺ is a positively charged cation, it readily undergoes electrostatic adsorption with negatively charged sites on the precipitate surface, such as forming surface-adsorbed lithium with ≡Al–O⁻, adsorbed F⁻, or other negatively charged sites. This process can be represented as: ≡Al–O⁻ + Li⁺ → ≡Al–O⁻···Li⁺, thereby enriching Li⁺ on the surface of the hydroxyl aluminum fluoride colloidal particles.

[0005] Meanwhile, aluminum hydroxyfluoride colloidal precipitates are characterized by fine particle size, high hydration, loose floc structure, and poor filtration performance, easily entraining large amounts of lithium-containing mother liquor. Under alkaline conditions, the colloidal polymer network formed may also encapsulate some lithium-containing liquid within the precipitate, causing lithium to enter the solid phase with the filter residue in adsorbed, entrained, or encapsulated forms, resulting in a decrease in the lithium content of the purified liquid. Traditional alkaline impurity removal processes often only focus on the removal rate of impurities such as Al and F, neglecting the correlation between the interfacial charge, Zeta potential, particle size evolution, filtration performance, and lithium loss from the filter residue of aluminum hydroxyfluoride colloidal precipitates. Therefore, even if impurities such as Al and F can be effectively removed, the recovery rate of subsequent lithium salt products is still reduced due to lithium loss with the colloidal precipitation. Existing lithium-containing leaching processes for aluminum electrolysis waste achieve a comprehensive lithium recovery rate of only about 60%–70%, resulting in low economic efficiency and resource recovery efficiency for lithium extraction.

[0006] Therefore, it is necessary to develop a method to improve the lithium recovery rate in lithium-containing waste residue from aluminum electrolysis, reduce the adsorption and entrainment loss of lithium in hydroxyl aluminum fluoride colloidal precipitation during the alkali purification process, and improve the lithium retention rate in the purification solution and the recovery rate of subsequent lithium salt products while effectively removing impurities such as Al and F. Summary of the Invention

[0007] (a) Purpose of the invention

[0008] The purpose of this invention is to provide a method for improving the lithium recovery rate in lithium-containing waste residue from aluminum electrolysis. Addressing the issues of fine particle size, strong surface negative charge, and easy adsorption and entrainment of Li⁺ by the hydroxyaluminum fluoride colloidal precipitate formed during the alkali purification process of lithium-containing leachate, a cationic interface modifier is introduced. This modifier preferentially adsorbs onto the negative potential points on the surface of the colloidal precipitate, reducing the absolute value of the zeta potential of the precipitate particles and weakening the electrostatic adsorption of Li⁺ by the precipitate. Simultaneously, it promotes the flocculation and growth of colloidal particles, improving sedimentation and filtration performance, reducing the amount of lithium entrained in the filter residue, and increasing the lithium retention rate in the purified lithium-containing solution.

[0009] (II) Technical Solution

[0010] To achieve the above objectives, the present invention adopts the following technical solution.

[0011] A method for improving lithium recovery rate in lithium-containing waste residue from aluminum electrolysis includes the following steps:

[0012] 1. A method for improving the lithium recovery rate in lithium-containing waste residue from aluminum electrolysis, characterized by comprising the following steps:

[0013] S1. Providing an acid leaching solution for aluminum electrolysis waste, wherein the lithium-containing leaching solution contains Li + Al-F complex ions, Na + A basic regulator is added to the lithium-containing leachate to cause the Al-F complex ions to undergo hydrolysis, hydroxyl substitution, or co-precipitation reactions to form hydroxyl aluminum fluoride precipitate.

[0014] S2. During the alkali addition process, a cationic interface modifier is added simultaneously, so that the cationic groups in the cationic interface modifier are adsorbed onto the negative potential points on the surface of the aluminum hydroxy fluoride colloidal precipitate, thereby regulating the Zeta potential of the colloidal precipitate.

[0015] S3. After aging, flocculation sedimentation and solid-liquid separation, purified lithium-containing liquid and aluminum hydroxy fluoride precipitate filter residue are obtained;

[0016] S4. The purified lithium-containing liquid is evaporated and concentrated to obtain a lithium concentrate;

[0017] S5. Add a lithium precipitation agent to the lithium concentrate to carry out a lithium precipitation reaction, and obtain a lithium salt product after solid-liquid separation;

[0018] 2. In this invention, the lithium-containing leachate is obtained by leaching one or a mixture of waste aluminum electrolyte, anode carbon slag, and overhaul slag, or by inorganic acid leaching, organic acid leaching, and aluminum salt solution leaching.

[0019] 3. In this invention, the Li⁺ concentration in the lithium-containing leachate is 0.05~20 g / L, the Al ion concentration (calculated as Al) is 0.05~30 g / L, and the F ion concentration (calculated as F) is 0.05~50 g / L.

[0020] 4. In this invention, the alkalinity regulator is one or more of sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate, sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, calcium oxide, calcium hydroxide, magnesium oxide, and magnesium hydroxide.

[0021] 5. In this invention, the cationic interface modifier is one or more of the following: cationic polyacrylamide, polydimethyldiallylammonium chloride, polyethyleneimine, quaternized chitosan, cationic starch, cationic cellulose, hexadecyltrimethylammonium bromide, and dodecyltrimethylammonium chloride.

[0022] 6. In this invention, the amount of cationic interface modifier added is 1~5000 mg / L of the volume of the lithium-containing leachate; the cationic interface modifier is added simultaneously with the alkaline regulator by means of one-time addition, segmented addition, or continuous dripping.

[0023] 7. In this invention, the solid-liquid separation method in step S3 is natural sedimentation, centrifugation, pressure filtration, vacuum filtration, membrane filtration, or a combination thereof.

[0024] 8. In this invention, after purifying the lithium-containing liquid and concentrating it, sodium carbonate, potassium carbonate, ammonium carbonate, ammonium bicarbonate, or carbon dioxide is introduced to prepare lithium carbonate products.

[0025] (III) Mechanism of Action

[0026] The mechanism of action of this invention is as follows:

[0027] In lithium-containing leachates, Al and F ions typically exist as aluminum-fluorine complexes. During the alkali purification process, these complexes undergo hydroxyl substitution and hydrolytic polymerization, forming a low-crystallinity hydroxylated aluminum fluoride colloidal precipitate. This type of precipitate exhibits numerous ≡Al-OH, ≡Al-F, ≡Al-O⁻, and adsorbed F⁻ / OH⁻ sites on its surface. The precipitate particles are negatively charged, exhibiting a large absolute value of the Zeta potential, strong electrostatic repulsion between particles, and high colloidal dispersion stability.

[0028] When a cationic interface modifier is added, the quaternary ammonium salt groups, protonated amino groups, or other cationic groups in the modifier can preferentially adsorb onto the negative potential points on the surface of hydroxyl aluminum fluoride colloidal particles. Through charge neutralization, double-layer compression, and polymer bridging, the Zeta potential shifts from a large negative value to near 0. This weakens the electrostatic adsorption of Li⁺ on the surface of the hydroxyl aluminum fluoride colloidal precipitate, reducing Li⁺ enrichment on the precipitate surface. Furthermore, it reduces the electrostatic repulsion between colloidal particles, promoting flocculation and particle size growth, thereby improving settling velocity and filtration performance, reducing the moisture content of the filter cake and the amount of lithium-containing mother liquor entrained, ultimately reducing the adsorbed or entrained lithium content in the filter residue and increasing the lithium retention rate of the purified liquid.

[0029] Therefore, this invention starts with the interfacial electrical regulation of aluminum hydroxyfluoride colloidal precipitation, and uses cationic interfacial modifiers to adjust its zeta potential and particle aggregation behavior, so as to synergistically solve the problems of difficult sedimentation, difficult filtration, and lithium entrainment loss of aluminum hydroxyfluoride colloidal precipitation during the lithium extraction process.

[0030] The beneficial effects of this invention are:

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] Reduce lithium entrainment loss: Cationic interface modifiers can neutralize the negative potential points on the surface of hydroxyl aluminum fluoride colloids, weaken their electrostatic adsorption of Li⁺, and reduce the entrainment of lithium-containing mother liquor by colloidal filter residue, thereby improving the lithium retention rate in the purified liquid.

[0033] Improved solid-liquid separation performance: By adjusting the Zeta potential, the precipitated particles are transformed from a stable colloidal state to a state that is prone to flocculation and aggregation, resulting in increased particle size, sedimentation rate, and filtration rate.

[0034] Reduced liquid content in filter cake: The modified precipitate flocs have a more porous and filterable structure, resulting in a lower liquid content in the filter cake and reduced lithium mother liquor entrainment.

[0035] Improve the efficiency of subsequent lithium precipitation and product purity: After modification and purification, the Al and F impurities in the lithium-containing liquid are reduced, and the lithium loss is reduced, which is beneficial to the subsequent preparation of lithium carbonate or other lithium salt products. Detailed Implementation

[0036] The present invention will be further described below with reference to embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. All equivalent substitutions, parameter adjustments, or process combinations made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0037] Example 1

[0038] Take 1 L of fluorine- and lithium-containing leachate obtained from acid leaching of waste aluminum electrolyte, wherein the Li⁺ concentration is 0.102 g / L, the Al concentration (calculated as Al) is 1.86 g / L, the F concentration (calculated as F) is 4.25 g / L, and the Na⁺ concentration is 8.60 g / L. Place the lithium-containing leachate in a reactor equipped with a stirrer, heat it to 60°C, and control the stirring speed at 300 r / min.

[0039] A 5% (w / w) sodium hydroxide solution was slowly added dropwise to the lithium-containing leachate to adjust the pH of the system to 7.0. Simultaneously, an aqueous solution of cationic polyacrylamide was added to achieve an effective concentration of 60 mg / L of cationic polyacrylamide in the system. After the solution reached pH 7.0, it was aged at 60°C for 60 min to allow the hydroxyl aluminum fluoride colloidal precipitate to agglomerate.

[0040] After aging, the slurry was vacuum filtered to obtain purified lithium-containing liquid and aluminum hydroxyfluoride precipitate filter residue. The filter residue was washed twice with deionized water, and the washing liquid was returned to the purified lithium-containing liquid. Testing showed that after adding cationic polyacrylamide, the Zeta potential of the suspension containing aluminum hydroxyfluoride colloid was adjusted from -31.5 mV under unmodified conditions to -6.9 mV, and the D50 particle size of the precipitate increased from 2.4 μm to 17.8 μm. The Li⁺ concentration in the purified lithium-containing liquid was 0.096 g / L, with a lithium retention rate of 94.1%; the lithium content in the filter residue, calculated as Li, was 0.018%.

[0041] The purified lithium-containing liquid was concentrated through multi-stage evaporation to increase the Li⁺ concentration to approximately 18 g / L. Then, the temperature was raised to 85°C, and sodium carbonate solution was added to carry out the lithium precipitation reaction. After reacting for 60 min, the solution was filtered, washed, and dried to obtain the lithium carbonate product. The overall lithium recovery rate in the product was 89.4%.

[0042] This embodiment demonstrates that in an ultra-low concentration lithium-containing system with a Li⁺ concentration of approximately 0.1 g / L, cationic polyacrylamide can effectively reduce the absolute value of the Zeta potential of hydroxyl aluminum fluoride colloidal precipitation, improve precipitation filtration performance, and reduce lithium loss due to entrainment in the filter residue.

[0043] Example 2

[0044] Take 1 L of the fluorine- and lithium-containing leachate obtained from the acid leaching of anode carbon slag, wherein the Li⁺ concentration is 0.098 g / L, the Al concentration (calculated as Al) is 1.20 g / L, the F concentration (calculated as F) is 3.15 g / L, and the Na⁺ concentration is 6.80 g / L. Heat the lithium-containing leachate to 50°C and control the stirring speed at 400 r / min.

[0045] Ammonia solution was slowly added dropwise to the lithium-containing leachate to adjust the pH of the system to 7.5. Simultaneously, polydimethyldiallylammonium chloride aqueous solution was added to achieve an effective concentration of 50 mg / L in the system. After the solution reached pH 7.5, it was aged at 50°C for 90 min to allow the hydroxyl aluminum fluoride colloidal precipitate to agglomerate.

[0046] After the slurry was allowed to settle for 30 min, it was filtered to obtain purified lithium-containing liquid and aluminum hydroxyl fluoride precipitate filter residue. Testing showed that after adding polydimethyldiallyl ammonium chloride, the Zeta potential of the suspension containing aluminum hydroxyl fluoride colloid decreased from -28.2 mV to -5.8 mV, and the D50 of the precipitate particles increased from 2.9 μm to 20.6 μm. The Li⁺ concentration in the purified lithium-containing liquid was 0.092 g / L, with a lithium retention rate of 93.9%; the lithium content in the filter residue (calculated as Li) was 0.016%.

[0047] The purified lithium-containing liquid was concentrated through multi-stage evaporation to increase the Li⁺ concentration to approximately 18 g / L. Then, the temperature was raised to 85°C, and sodium carbonate solution was added to carry out the lithium precipitation reaction. After reacting for 60 min, the solution was filtered, washed, and dried to obtain the lithium carbonate product. The overall lithium recovery rate in the product was 88.2%.

[0048] Example 3

[0049] Two L of fluorine- and lithium-containing leachate obtained from the acid leaching of lithium-rich aluminum electrolyte replacement residue was taken, wherein the Li⁺ concentration was 0.101 g / L, the Al concentration (calculated as Al) was 2.35 g / L, the F concentration (calculated as F) was 5.10 g / L, and the Na⁺ concentration was 10.40 g / L. The lithium-containing leachate was heated to 65 °C, and the stirring speed was controlled at 300 r / min.

[0050] Sodium hydroxide solution was slowly added to the lithium-containing leachate to adjust the pH of the system to 7.2. The reaction was kept at the temperature for 20 min to allow some of the aluminum-fluorine complex to hydrolyze. Polyethyleneimine aqueous solution was added simultaneously during the process to make its effective concentration 40 mg / L. The mixture was then aged at 65 °C for 90 min and filtered.

[0051] Testing revealed that the synergistic effect of slow alkali addition and a cationic interface modifier effectively prevented the explosive nucleation of hydroxyl aluminum fluoride colloids caused by rapid alkali addition. The zeta potential of the resulting precipitate particles was adjusted from -33.0 mV to -6.1 mV, and the D50 increased to 24.5 μm. The Li⁺ concentration in the purified lithium-containing solution was 0.096 g / L, with a lithium retention rate of 95.0%; the lithium content in the filter residue, calculated as Li, was 0.015%.

[0052] The purified lithium-containing liquid was concentrated through multi-stage evaporation to increase the Li⁺ concentration to approximately 20 g / L. Then, the temperature was raised to 85°C, and sodium carbonate solution was added to carry out a lithium precipitation reaction. After reacting for 60 min, the solution was filtered, washed, and dried to obtain lithium carbonate product. The overall lithium recovery rate in the product was 89.1%.

[0053] Example 4

[0054] One L of a fluorine- and lithium-containing leachate was obtained by leaching lithium-containing waste residue from aluminum electrolysis with an aluminum salt solution. The concentration of Li⁺ was 0.097 g / L, the concentration of Al (calculated as Al) was 1.75 g / L, the concentration of F (calculated as F) was 4.60 g / L, and the concentration of Na⁺ was 9.20 g / L. The lithium-containing leachate was heated to 70 °C, and the stirring speed was controlled at 500 r / min.

[0055] Subsequently, a 5% sodium hydroxide solution was slowly added to adjust the pH of the system to 7.3. During the process, cetyltrimethylammonium bromide and cationic polyacrylamide were added to the system simultaneously to make the effective concentration of cetyltrimethylammonium bromide 20 mg / L and the effective concentration of cationic polyacrylamide 40 mg / L.

[0056] After aging, filtration was performed to obtain a filter residue containing purified lithium-containing liquid and hydroxyl aluminum fluoride precipitate. Testing showed that the addition of hexadecyltrimethylammonium bromide and cationic polyacrylamide adjusted the zeta potential of the precipitate particles from -35.4 mV to -5.2 mV, increased the particle size (D50) to 29.6 μm, and significantly improved the pressure filtration rate. The Li⁺ concentration in the purified lithium-containing liquid was 0.091 g / L, with a lithium retention rate of 93.8%; the lithium content in the filter residue (calculated as Li) was 0.017%.

[0057] The purified lithium-containing liquid was concentrated through multi-stage evaporation to increase the Li⁺ concentration to approximately 20 g / L. Then, the temperature was raised to 85°C, and sodium carbonate solution was added to carry out the lithium precipitation reaction. After reacting for 60 min, the solution was filtered, washed, and dried to obtain the lithium carbonate product. The overall lithium recovery rate in the product was 91.7%.

[0058] Comparative Example 1

[0059] Except for the absence of a cationic interface modifier, the other conditions were the same as in Example 1. Specifically, 1 L of the same lithium-containing leachate was taken, and a 5% sodium hydroxide solution was slowly added dropwise at 60 °C and 300 r / min to adjust the pH to 7.0. The mixture was then aged for 60 min and vacuum filtered.

[0060] Testing showed that without the addition of a cationic interface modifier, the zeta potential of the hydroxyl aluminum fluoride colloidal precipitation was -31.5 mV, the particle D50 was 2.4 μm, and the filtration time was 38 min. The Li⁺ concentration in the purified lithium-containing solution was 0.083 g / L, and the lithium retention rate was 81.4%; the lithium content in the filter residue, calculated as Li, was 0.052%.

[0061] The purified lithium-containing liquid was concentrated through multi-stage evaporation to increase the Li⁺ concentration to approximately 18 g / L. Then, the temperature was raised to 85°C, and sodium carbonate solution was added to carry out the lithium precipitation reaction. After reacting for 60 min, the solution was filtered, washed, and dried to obtain the lithium carbonate product. The overall lithium recovery rate in the product was 75.7%.

[0062] Comparative Example 2

[0063] Except for replacing cationic polyacrylamide with anionic polyacrylamide, the other conditions were the same as in Example 1. The effective concentration of anionic polyacrylamide was 60 mg / L.

[0064] Testing revealed that after adding anionic polyacrylamide, the Zeta potential of the hydroxyl-fluorinated aluminum colloidal precipitation was -38.7 mV, a further negative shift compared to the condition without the modifier. This indicated enhanced particle dispersion stability, reduced sedimentation rate, and a filtration time of 45 min. The purified lithium-containing solution contained a Li⁺ concentration of 0.080 g / L, with a lithium retention rate of 78.4%. The lithium content in the filter residue, calculated as Li, was 0.061%.

[0065] The purified lithium-containing liquid was concentrated through multi-stage evaporation to increase the Li⁺ concentration to approximately 18 g / L. Then, the temperature was raised to 85°C, and sodium carbonate solution was added to carry out a lithium precipitation reaction. After reacting for 60 min, the solution was filtered, washed, and dried to obtain lithium carbonate product. The overall lithium recovery rate in the product was 67.8%.

[0066] Comparative Example 3

[0067] Except for increasing the amount of cationic polyacrylamide added to 1500 mg / L, the other conditions were the same as in Example 1.

[0068] Testing revealed that after excessive addition of cationic polyacrylamide, the Zeta potential of the precipitated particles changed from negative to +16.8 mV, indicating a charge reversal in the system. The flocs became viscous, and the filtration performance did not improve further, with a filtration time of 27 min. The Li⁺ concentration in the purified lithium-containing solution was 0.077 g / L, with a lithium retention rate of 75.5%; the lithium content in the filter residue, calculated as Li, was 0.039%.

[0069] The purified lithium-containing liquid was concentrated through multi-stage evaporation to increase the Li⁺ concentration to approximately 18 g / L. Then, the temperature was raised to 85°C, and sodium carbonate solution was added to carry out a lithium precipitation reaction. After reacting for 60 min, the solution was filtered, washed, and dried to obtain lithium carbonate product. The overall lithium recovery rate in the product was 66.8%.

Claims

1. A method for improving the lithium recovery rate in lithium-containing waste residue from aluminum electrolysis, characterized in that, Includes the following steps: S1. Providing an acid leaching solution for aluminum electrolysis waste, wherein the lithium-containing leaching solution contains Li + Al-F complex ions, Na + A basic regulator is added to the lithium-containing leachate to cause the Al-F complex ions to undergo hydrolysis, hydroxyl substitution, or co-precipitation reactions to form hydroxyl aluminum fluoride precipitate. S2. During the alkali addition process, a cationic interface modifier is added simultaneously, so that the cationic groups in the cationic interface modifier are adsorbed onto the negative potential points on the surface of the aluminum hydroxy fluoride colloidal precipitate, thereby regulating the Zeta potential of the colloidal precipitate. S3. After aging, flocculation sedimentation and solid-liquid separation, purified lithium-containing liquid and aluminum hydroxy fluoride precipitate filter residue are obtained; S4. The purified lithium-containing liquid is evaporated and concentrated to obtain a lithium concentrate; S5. Add a lithium precipitation agent to the lithium concentrate to carry out a lithium precipitation reaction, and obtain a lithium salt product after solid-liquid separation.

2. The method according to claim 1, characterized in that, The lithium-containing leachate is derived from one or a mixture of waste aluminum electrolyte, anode carbon slag, and overhaul slag, and is obtained by inorganic acid leaching, organic acid leaching, and aluminum salt solution leaching.

3. The method according to claim 1, characterized in that, The lithium-containing leachate has a Li⁺ concentration of 0.05~20 g / L, an Al ion concentration of 0.05~30 g / L (calculated as Al), and an F ion concentration of 0.05~50 g / L (calculated as F).

4. The method according to claim 1, characterized in that, The alkalinity regulator is one or more of the following: sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate, sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, calcium oxide, calcium hydroxide, magnesium oxide, and magnesium hydroxide.

5. The method according to claim 1, characterized in that, The cationic interface modifier is one or more of the following: cationic polyacrylamide, polydimethyldiallylammonium chloride, polyethyleneimine, quaternized chitosan, cationic starch, cationic cellulose, hexadecyltrimethylammonium bromide, and dodecyltrimethylammonium chloride.

6. The method according to claim 1, characterized in that, The amount of the cationic interface modifier added is 1~5000 mg / L of the lithium-containing leaching solution volume; the cationic interface modifier is added simultaneously with the alkaline regulator in the form of one-time addition, segmented addition, or continuous dripping.

7. The method according to claim 1, characterized in that, The solid-liquid separation method described in step S3 is natural sedimentation, centrifugation, pressure filtration, vacuum filtration, membrane filtration, or a combination thereof.

8. The method according to claim 1, characterized in that, The purified lithium-containing liquid is concentrated and then sodium carbonate, potassium carbonate, ammonium carbonate, ammonium bicarbonate, or carbon dioxide is introduced to prepare lithium carbonate products.