Method for selectively extracting lithium from lepidolite

Abstract

The invention belongs to the technical field of lithium-containing mineral treatment, and relates to a method for selectively extracting lithium from lepidolite. The method mainly comprises the following steps: carrying out roasting defluorination treatment on lepidolite, and grinding to obtain a lepidolite defluorination roasting material in which the mass content of lithium is 0.8-1.5% and the mass content of aluminum is 20-30%; carrying out acid leaching treatment on the lepidolite defluorination roasting material by using a first acid solution, and carrying out solid-liquid separation to obtain a leaching solution and leaching residues; adjusting the pH value of the leachate to 2-3 by adopting a neutralizer, and then adding a mixture of the neutralizer and benzoic acid into the leachate to obtain aluminum benzoate precipitate and aluminum-removed liquid; adding the aluminum benzoate precipitate into a second acid solution, dissolving, and carrying out solid-liquid separation to obtain regenerated benzoic acid and an aluminum-rich solution; and cooling the aluminum-rich solution to obtain an aluminum salt and a recyclable acid solution. According to the method, efficient separation of lithium and aluminum in lepidolite can be achieved, benzoic acid and the acid solution can be recycled, and the lithium extraction cost can be effectively reduced.

Description

Technical Field

[0001] The present application belongs to the technical field of lithium-containing mineral processing, and specifically relates to a method for selectively extracting lithium from lepidolite. Background Art

[0002] Lithium is a vital metallic element in modern industry, widely used in new energy, metallurgy, defense, and military sectors. With the rapid growth in demand for lithium-ion batteries, increasing lithium mine production has become a key approach to easing demand for lithium products. Efficient lithium extraction from lithium minerals such as lepidolite is crucial to the stability of the lithium resource market.

[0003] Lepidolite's complex composition and low grade make separation and recovery of its valuable components difficult. Existing lepidolite extraction processes are generally plagued by low extraction efficiency, severe environmental pollution, and high costs. Based on these issues, this application proposes a method for selective lithium extraction from lepidolite, which can achieve efficient separation of lithium and aluminum from lepidolite and effectively reduce the cost of lithium extraction. Summary of the Invention

[0004] In view of this, the present application provides a method for selectively extracting lithium from lepidolite, which can achieve efficient separation of lithium and aluminum in lepidolite and effectively reduce the cost of lithium extraction.

[0005] The method in this application comprises the following steps:

[0006] S1: calcining and defluorinating lepidolite, grinding, and obtaining a lepidolite defluorinating calcined material, wherein the lepidolite defluorinating calcined material has a lithium content of 0.8% to 1.5% and an aluminum content of 20% to 30% by mass;

[0007] S2: using the first acid solution to acid-leach the lepidolite defluorination roasted material, and obtaining a leachate and a leach residue after solid-liquid separation;

[0008] S3: adjusting the pH of the leachate to 2-3 with a neutralizer, then adding a mixture of the neutralizer and benzoic acid to the leachate, reacting at 40° C. to 80° C. for 60 min to 120 min to obtain an aluminum benzoate precipitate and an aluminum removal liquid, wherein the neutralizer is at least one of sodium carbonate and calcium carbonate, the mass ratio of benzoic acid to the neutralizer is (2.0-2.4):1, and the concentration of benzoic acid is 0.8 mol / L to 2.3 mol / L;

[0009] S4: adding the aluminum benzoate precipitate to the second acid solution, dissolving it at 60° C. to 80° C., and obtaining regenerated benzoic acid and aluminum-rich solution after solid-liquid separation;

[0010] S5: Cool the aluminum-rich solution to obtain aluminum salt and circulating liquid, which can be used in S2.

[0011] Through the method described in the present application, efficient separation of lithium and aluminum in lepidolite can be achieved, and both benzoic acid and acid solution can be recycled, which can effectively reduce the cost of lithium extraction. In the present application, lepidolite containing a certain amount of lithium and aluminum is first subjected to defluorination roasting and grinding treatment to obtain a lepidolite defluorination roasted material with a high degree of dissociation; then the lepidolite defluorination roasted material is subjected to acid leaching treatment using a first acid solution, and a leachate and a leach residue are obtained after solid-liquid separation. After the above treatment, most of the lithium and part of the aluminum in the lepidolite are transferred to the leachate; further, a neutralizer is used to adjust the pH of the leachate to 2-3, and then a mixture of a neutralizer and benzoic acid is added to the leachate. By controlling the various parameters in the reaction, aluminum benzoate precipitate and aluminum removal liquid can be obtained. After this step, aluminum is separated from lithium in the form of aluminum benzoate; further, the aluminum benzoate precipitate is added to the second acid solution, dissolved and reacted at a certain temperature, and regenerated benzoic acid and aluminum-rich solution are obtained after solid-liquid separation. The regenerated benzoic acid can be recycled, which greatly reduces the cost of lithium extraction. At the same time, by controlling the type of the second acid solution, aluminum benzoate can be converted into common aluminum salts; finally, the aluminum-rich solution is cooled. During the cooling process, the aluminum salt dissolved in the second acid solution at high temperature gradually precipitates to obtain aluminum salts and circulating liquid. The circulating liquid is an acid solution and can be repeatedly used in step S2.

[0012] In some embodiments, the particle size of the defluorinated calcined lepidolite material is between 200 mesh and 400 mesh. A suitable particle size allows the first acid solution to penetrate the lepidolite uniformly and quickly, thereby increasing the leaching speed and leaching rate.

[0013] In some embodiments, the fluorine content in the defluorinated calcined lepidolite is less than or equal to 1.5% by mass, based on the mass of the defluorinated calcined lepidolite. Controlling the fluorine content can avoid or mitigate HF generation corrosion to equipment and environmental pollution.

[0014] In some embodiments, the first acid solution is an aqueous sulfuric acid solution having a concentration of 1.5 mol / L to 2.5 mol / L. The concentration of the aqueous sulfuric acid solution described herein not only allows for a high leaching rate of lithium from the lepidolite, fully converting it into soluble lithium sulfate, but also prevents excessive dissolution of impurity elements, thereby reducing the difficulty of subsequent separation and purification.

[0015] In some embodiments, the acid leaching treatment satisfies at least one of the following conditions:

[0016] (1) The liquid-to-solid ratio of the first acid solution to the lepidolite defluorination roasted material is (5-10):1;

[0017] (2) The acid leaching temperature is 60℃~90℃;

[0018] (3) The acid leaching time is 60 minutes to 120 minutes.

[0019] A suitable liquid-to-solid ratio ensures sufficient reaction between the acid and the defluorinated lepidolite calcined material while controlling costs. Controlling the temperature within the aforementioned range accelerates the reaction while avoiding excessive energy consumption, balancing efficiency and cost. Controlling the acid leaching time within the aforementioned range ensures sufficient lithium dissolution while suppressing side reactions. Furthermore, through the coordinated regulation of these three factors, efficient lithium extraction can be achieved, production costs can be reduced, and environmental protection requirements can be met.

[0020] In some embodiments, the second acid solution in S4 is an aqueous sulfuric acid solution having a concentration of 0.5 mol / L to 2 mol / L. By using an aqueous sulfuric acid solution of this concentration, the aluminum benzoate precipitate is converted into an aluminum sulfate solution. Compared to aluminum benzoate, aluminum sulfate has a wider range of applications.

[0021] In some embodiments, the liquid-to-solid ratio of the second acid solution to the aluminum benzoate precipitate in S4 is (5-10):1; and / or the dissolution time is 90-120 minutes. By controlling the liquid-to-solid ratio of the second acid solution to the aluminum benzoate precipitate within the above range, and / or controlling the dissolution time, the aluminum benzoate fully reacts with the second acid solution, benzoic acid can be efficiently recovered from the aluminum benzoate, and the aluminum is fully dissolved in the second acid solution as aluminum ions.

[0022] In some embodiments, in S5, the aluminum-rich solution is cooled to 10° C. to 20° C. Aluminum salts have higher solubility at higher temperatures. At 10° C. to 20° C., the solubility of aluminum salts decreases, and a large amount of aluminum salts precipitate from the aluminum-rich solution to obtain solid aluminum salts.

[0023] Compared with the traditional lithium extraction method of lepidolite, the beneficial effects of this application include at least the following points:

[0024] (1) By defluorinating and roasting lepidolite in combination with acid leaching, most of the lithium in the lepidolite is transferred to the leachate, achieving high-efficiency leaching of lithium from the lepidolite;

[0025] (2) Through coordination regulation, aluminum in the leachate is separated from lithium in the form of aluminum benzoate precipitation, achieving efficient and simple separation of lithium and aluminum;

[0026] (3) The aluminum benzoate precipitate is converted into aluminum salt by acid treatment, and regenerated benzoic acid and circulating liquid are obtained at the same time. The regenerated benzoic acid and circulating liquid can be recycled;

[0027] (4) The process has low cost, simple operation and is suitable for large-scale industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A schematic diagram of the steps of a method for selective lithium extraction from lepidolite provided in this application;

[0029] Figure 2This is a relationship diagram of the leachate components and the amounts of benzoic acid and neutralizer added in one embodiment of the present application;

[0030] Figure 3 To regenerate benzoic acid. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0032] Furthermore, the terms "first," "second," etc., are primarily used to distinguish between different devices, elements, or components (which may or may not be of the same type and configuration), and are not intended to indicate or imply the relative importance or quantity of the devices, elements, or components indicated. Unless otherwise specified, "plurality" means two or more.

[0033] Currently, the main lithium extraction processes from lepidolite are acid leaching, lime roasting, and salt roasting. However, these processes generally have long process flows, large reagent consumption, high energy consumption, and high flue gas generation. Patent CN104876250A discloses a "method for extracting lithium and removing aluminum from lepidolite by treating it with sulfuric acid." The method involves mechanical activation of the lepidolite, low-temperature sulfuric acid leaching, medium-temperature sintering, tail gas recovery, and water leaching of lithium, achieving a lithium leaching rate of over 94%. The high-aluminum slag after alkali metal extraction is then prepared into building blocks. Patent CN109110787A discloses an "improved process for the lepidolite-limestone sintering method." The lepidolite concentrate is mixed and sintered with limestone having a CaO content greater than 53%. The clinker is then subjected to water extraction, wet grinding, leaching, filtration, and crystallization to ultimately obtain a lithium hydroxide product. Patent CN113636579A discloses a "new sulfate roasting process for preparing lithium carbonate from lepidolite." Lepidolite ore is mixed with a sodium-potassium sulfate mixture, additives, and calcium carbonate, granulated, roasted, and leached in water to produce a lithium sulfate mother liquor. The lithium carbonate product is then obtained through neutralization and impurity removal, evaporation concentration, and carbonate precipitation. While all of these processes can achieve lithium leaching, they generally suffer from lengthy process flows, high reagent and energy consumption, and significant flue gas generation.

[0034] Based on this, the present application provides a method for selectively extracting lithium from lepidolite, which can achieve efficient separation of lithium and aluminum in lepidolite and effectively reduce the cost of lithium extraction.

[0035] like Figure 1 As shown, the method in this application includes the following steps:

[0036] S1: calcining and defluorinating lepidolite, grinding, and obtaining a lepidolite defluorinating calcined material, wherein the lepidolite defluorinating calcined material has a lithium content of 0.8% to 1.5% and an aluminum content of 20% to 30% by mass;

[0037] S2: using the first acid solution to acid-leach the lepidolite defluorination roasted material, and obtaining a leachate and a leach residue after solid-liquid separation;

[0038] S3: adjusting the pH of the leachate to 2-3 with a neutralizer, then adding a mixture of the neutralizer and benzoic acid to the leachate, reacting at 40° C. to 80° C. for 60 min to 120 min to obtain an aluminum benzoate precipitate and an aluminum removal liquid, wherein the neutralizer is at least one of sodium carbonate and calcium carbonate, the mass ratio of benzoic acid to the neutralizer is (2.0-2.4):1, and the concentration of benzoic acid is 0.8 mol / L to 2.3 mol / L;

[0039] S4: adding the aluminum benzoate precipitate to the second acid solution, dissolving it at 60° C. to 80° C., and obtaining regenerated benzoic acid and aluminum-rich solution after solid-liquid separation;

[0040] S5: Cool the aluminum-rich solution to obtain aluminum salt and circulating liquid, which can be used in S2.

[0041] The inventors found that after defluorination roasting and grinding treatment, a defluorinated roasted material of lepidolite with a high degree of dissociation can be obtained. The defluorinated roasted material of lepidolite is subjected to acid leaching treatment using a first acid solution. The defluorinated roasted material of lepidolite with a high degree of dissociation is more easily reacted with acid, which can effectively improve the acid leaching efficiency. After the above-mentioned acid leaching treatment, most of the lithium and part of the aluminum in the lepidolite are transferred to the leachate. A neutralizer is used to adjust the pH of the leachate to 2-3, and then a mixture of a neutralizer and benzoic acid is added to the leachate. By controlling the various parameters in the reaction, aluminum benzoate precipitate and aluminum removal liquid are obtained. In this step, the pH of the leachate is adjusted, which is conducive to the occurrence of subsequent reactions, and the synergy between the various parameters is beneficial. The effect is that the aluminum in the leachate is basically separated from the lithium in the leachate in the form of aluminum benzoate precipitate; then, the aluminum benzoate precipitate is added to the second acid solution, dissolved and reacted at a certain temperature, and regenerated benzoic acid and aluminum-rich solution are obtained after solid-liquid separation. The regenerated benzoic acid can be recycled, which greatly reduces the cost of lithium extraction. At the same time, by controlling the type of the second acid solution, aluminum benzoate can be converted into common aluminum salts. For example, when the second acid solution is sulfuric acid, aluminum benzoate can be converted into aluminum sulfate; finally, the aluminum-rich solution is cooled. During the cooling process, the aluminum salt dissolved in the second acid solution at high temperature gradually precipitates to obtain aluminum salt and circulating liquid. The circulating liquid is an acid solution and can be repeatedly put into step S2 for use.

[0042] For example, the mass content of lithium can be any value within the above range, including but not limited to 0.8%, 1.0%, 1.2%, 1.3%, 1.5%, etc.; the mass content of aluminum can be any value within the above range, including but not limited to 20%, 21%, 24%, 27%, 28%, 30%, etc.; the pH of the leachate adjusted by the neutralizer can be any value within the above range, including but not limited to 2.0, 2.1, 2.3, 2.4, 2.7, 2.8, 3.0, etc.; the reaction temperature of the mixture of the leachate, the neutralizer and benzoic acid can be including but not limited to 40°C, 45°C, 50°C, 55°C, 60°C, 70°C, 80°C, etc.; the reaction temperature of the leachate, the neutralizer and benzoic acid can be including but not limited to 40°C, 45°C, 50°C, 55°C, 60°C, 70°C, 80°C, etc. The reaction time of the mixture includes but is not limited to 60 min, 70 min, 80 min, 100 min, 120 min, etc.; the mass ratio of benzoic acid to neutralizer can be 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, etc., and the concentration of benzoic acid can be any value within the above range, including but not limited to 0.8 mol / L, 1.1 mol / L, 1.4 mol / L, 2.0 mol / L, 2.3 mol / L, etc.; the dissolution temperature of the aluminum benzoate precipitate in the second acid solution can be any value within the above range, including but not limited to 60°C, 62°C, 64°C, 68°C, 70°C, 73°C, 78°C, 80°C, etc.

[0043] In some embodiments, the particle size of the lepidolite defluorination roasted material is between 200 mesh and 400 mesh. The appropriate particle size can allow the first acid solution to penetrate the lepidolite uniformly and quickly, thereby improving the leaching speed and leaching rate. For example, the particle size of the lepidolite defluorination roasted material can be any point value within the above range, including but not limited to 200 mesh, 220 mesh, 240 mesh, 270 mesh, 300 mesh, 320 mesh, 380 mesh, 390 mesh, 400 mesh, etc.

[0044] In some embodiments, the lepidolite defluorination calcined material has a fluorine content of less than or equal to 1.5% by mass, based on the mass of the lepidolite defluorination calcined material. Controlling the fluorine content can avoid or mitigate HF generation, which can cause corrosion to equipment and environmental pollution. This application does not limit the defluorination method of the lepidolite.

[0045] In some embodiments, the first acid solution is an aqueous sulfuric acid solution, and the concentration of the aqueous sulfuric acid solution is 1.5 mol / L to 2.5 mol / L. The concentration of the aqueous sulfuric acid solution described in the present application can not only achieve a high leaching rate of lithium in the lepidolite and fully convert it into soluble lithium sulfate, but also avoid excessive dissolution of impurity elements, reducing the difficulty of subsequent separation and purification. Exemplarily, the concentration of the aqueous sulfuric acid solution can be 1.5 mol / L, 1.8 mol / L, 2.0 mol / L, 2.2 mol / L, 2.5 mol / L, etc.

[0046] In some embodiments, the acid leaching treatment satisfies at least one of the following conditions:

[0047] (1) The liquid-to-solid ratio of the first acid solution to the lepidolite defluorination roasted material is (5-10):1;

[0048] (2) The acid leaching temperature is 60℃~90℃;

[0049] (3) The acid leaching time is 60 minutes to 120 minutes.

[0050] A suitable liquid-to-solid ratio can ensure sufficient reaction between the acid solution and the lepidolite defluorination roasted material while controlling costs; controlling the temperature within the above range can accelerate the reaction speed while avoiding excessive energy consumption, balancing efficiency and cost; controlling the acid leaching time within the above range can both fully dissolve lithium and inhibit the occurrence of side reactions. Furthermore, through the coordinated regulation of the three, efficient lithium extraction can be achieved, production costs can be reduced, and environmental protection requirements can be met. For example, the liquid-to-solid ratio of the first acid solution to the lepidolite defluorination roasted material can be 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, etc.; the acid leaching temperature can be any value within the above range, including but not limited to 60°C, 65°C, 70°C, 75°C, 78°C, 85°C, 90°C, etc.; the acid leaching time can be any value within the above range, including but not limited to 60 minutes, 70 minutes, 77 minutes, 82 minutes, 95 minutes, 110 minutes, 120 minutes, etc.

[0051] In some embodiments, the second acid solution in S4 is an aqueous sulfuric acid solution having a concentration of 0.5 mol / L to 2 mol / L. By using an aqueous sulfuric acid solution of this concentration, the aluminum benzoate precipitate is converted into an aluminum sulfate solution. Compared to aluminum benzoate, aluminum sulfate has a wider range of applications. For example, the concentration of the aqueous sulfuric acid solution can be 0.5 mol / L, 0.8 mol / L, 1.1 mol / L, 1.3 mol / L, 1.8 mol / L, 2.0 mol / L, etc.

[0052] In some embodiments, the liquid-to-solid ratio of the second acid solution and the aluminum benzoate precipitate in S4 is (5-10):1; and / or the dissolution time is 90-120 min. By controlling the liquid-to-solid ratio of the second acid solution and the aluminum benzoate precipitate within the above range, the aluminum benzoate fully reacts with the second acid solution, benzoic acid can be efficiently recovered from the aluminum benzoate, and the aluminum is fully dissolved in the second acid solution in the form of aluminum ions. Exemplarily, the liquid-to-solid ratio of the second acid solution and the aluminum benzoate precipitate can be any value within the above range, including but not limited to 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, etc.; the dissolution time can be any value within the above range, including but not limited to 90 min, 95 min, 100 min, 110 min, 120 min, etc.

[0053] In some embodiments, in S5, the aluminum-rich solution is cooled to 10° C. to 20° C. Aluminum salts have higher solubility at higher temperatures. At 10° C. to 20° C., the solubility of aluminum salts is lower, and a large amount of aluminum salts precipitate from the aluminum-rich solution to obtain solid aluminum salts.

[0054] The scheme of the present application is described below with reference to the following specific examples. Unless otherwise specified, the raw materials used in the following examples are all from common commercial products, and the devices or equipment used are all purchased from conventional market sales channels.

[0055] Example 1

[0056] The process flow of selective lithium extraction from defluorinated calcined lepidolite is as follows: Figure 1 As shown. The particle size of the lithium mica defluorinated roasted material after grinding is 300 mesh, and the main components are Li: 1.32%, Al: 26.63%, F: 1.0% in mass percentage. The lithium mica defluorinated roasted material was acid leached, and the sulfuric acid concentration was controlled to 2.0 mol / L, the liquid-solid ratio was 10:1, the leaching temperature was 90 ° C, the leaching was 120 min, and the solid-liquid separation was performed to obtain the leachate and the leach residue. The leaching rates of Li and Al were 92.3% and 31.2%, respectively. The pH of the leachate was adjusted to 2.7, and then a mixture of benzoic acid and calcium carbonate was added. The mass ratio of benzoic acid to calcium carbonate was 2.2:1. The initial benzoic acid concentration in the solution was controlled to 0.83 mol / L, the precipitation temperature was 60 ° C, and the precipitation time was 90 min. Aluminum benzoate precipitate and aluminum removal liquid were obtained. The aluminum removal rate was 99.5%, and the lithium loss rate was 0.5%. The relationship between the aluminum removal process parameters and the aluminum removal rate and lithium loss rate is shown as follows. Figure 2 The concentrations of lithium and aluminum in the leaching solution and the aluminum removal solution are shown in Table 1. The aluminum benzoate precipitate was dissolved in 1.5 mol / L sulfuric acid with a liquid-solid ratio of 10:1, a reaction temperature of 80°C, and a dissolution time of 90 min. After solid-liquid separation, regenerated benzoic acid and solution were obtained. The benzoic acid regeneration rate was 99%. The photo of the regenerated benzoic acid is shown in Figure 1. Figure 3 Benzoic acid is returned to the precipitation step, the solution is cooled to 15°C, and the solid-liquid separation is performed to obtain aluminum salt and circulating liquid.

[0057] Example 2

[0058] The defluorinated calcined lepidolite material was ground to a particle size of 400 mesh. Its main components, by mass percentage, were 0.8% Li, 30% Al, and 1.5% F. The defluorinated calcined lepidolite material was acid-leached with a sulfuric acid concentration of 2.5 mol / L, a liquid-to-solid ratio of 7.5:1, a leaching temperature of 80°C, and a leaching time of 90 min. Solid-liquid separation yielded a leachate and a leached residue. The leaching rates of Li and Al were 90.4% and 43.5%, respectively. The leachate pH was adjusted to 3.0, and a mixture of benzoic acid and sodium carbonate was added at a benzoic acid:sodium carbonate mass ratio of 2.0:1. The initial benzoic acid concentration in the solution was controlled at 2.3 mol / L. The precipitation temperature was 40°C, and the precipitation time was 120 min. This yielded an aluminum benzoate precipitate and an aluminum removal solution. The aluminum removal rate was 99.8%, with a lithium loss rate of 6.8%. The lithium and aluminum concentrations in the leachate and aluminum removal solution are shown in Table 1. The aluminum benzoate precipitate was dissolved in 0.5 mol / L sulfuric acid at a liquid-to-solid ratio of 7.5:1. The reaction temperature was 90°C and the dissolution time was 6 minutes. After solid-liquid separation, regenerated benzoic acid and a solution were obtained. The benzoic acid regeneration rate was 93%. The benzoic acid was returned to the precipitation step, and the solution was cooled to 10°C. The aluminum salt and the circulating liquid were separated by solid-liquid separation.

[0059] Example 3

[0060] The defluorinated calcined lepidolite material was ground to a particle size of 200 mesh. Its main components, by mass percentage, were 1.47% Li, 21.35% Al, and 0.5% F. The defluorinated calcined lepidolite material was acid-leached with a sulfuric acid concentration of 1.5 mol / L, a liquid-to-solid ratio of 5:1, a leaching temperature of 60°C, and a leaching time of 60 min. Solid-liquid separation yielded a leachate and a leached residue. The leaching rates of Li and Al were 91.5% and 30.1%, respectively. The leachate pH was adjusted to 2.0, and a mixture of benzoic acid and sodium carbonate was added at a benzoic acid:sodium carbonate mass ratio of 2.4:1. The initial benzoic acid concentration in the solution was controlled at 1.43 mol / L. The precipitation temperature was maintained at 80°C for 60 min, resulting in an aluminum benzoate precipitate and an aluminum removal solution. The aluminum removal rate was 99.1%, and the lithium loss rate was 1.0%. The lithium and aluminum concentrations in the leachate and aluminum removal solution are shown in Table 1. The aluminum benzoate precipitate was dissolved in 2.0 mol / L sulfuric acid at a liquid-to-solid ratio of 5:1. The reaction temperature was 60°C and the dissolution time was 120 minutes. After solid-liquid separation, regenerated benzoic acid and a solution were obtained. The benzoic acid regeneration rate was 95%. The benzoic acid was returned to the precipitation step, and the solution was cooled to 20°C. The aluminum salt and the circulating liquid were separated by solid-liquid separation.

[0061] Table 1

[0062]

[0063] Referring to Examples 1 to 3 and Table 1, it can be seen that:

[0064] (1) The leaching rates of Li from lepidolite were 92.3%, 90.4%, and 91.5%, respectively. More than 90% of Li was transferred from the defluorinated calcined lepidolite to the leachate, resulting in a high leaching rate.

[0065] (2) The Li loss rates before and after aluminum removal were 0.5%, 6.8%, and 1.0%, respectively, while the aluminum removal rates were 99.5%, 99.8%, and 99.10%, respectively. Most of the aluminum was transferred out of the leachate with minimal lithium loss, indicating that lithium and aluminum in the leachate were efficiently separated.

[0066] (3) The recovery rates of benzoic acid are 99%, 93% and 95% respectively. The recovery rates are relatively high and benzoic acid can be recycled, which can effectively reduce process costs.

[0067] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for selectively extracting lithium from lepidolite, characterized in that: The method comprises the following steps: S1: calcining and defluorinating the lepidolite, grinding the lepidolite to obtain a lepidolite defluorination calcined material, wherein the lepidolite defluorination calcined material has a lithium content of 0.8% to 1.5% and an aluminum content of 20% to 30% by mass; S2: using a first acid solution to acid-leach the lepidolite defluorination roasted material, and obtaining a leachate and a leach residue after solid-liquid separation; S3: adjusting the pH of the leachate to 2-3 with a neutralizer, then adding a mixture of the neutralizer and benzoic acid to the leachate, and reacting at 40° C. to 80° C. for 60 min to 120 min to obtain an aluminum benzoate precipitate and an aluminum removal liquid, wherein the neutralizer is at least one of sodium carbonate and calcium carbonate, the mass ratio of the benzoic acid to the neutralizer is (2.0-2.4):1, and the concentration of the benzoic acid is 0.8 mol / L to 2.3 mol / L; S4: adding the aluminum benzoate precipitate to a second acid solution, dissolving it at 60° C. to 80° C., and obtaining regenerated benzoic acid and an aluminum-rich solution after solid-liquid separation; S5: Cool the aluminum-rich solution to obtain aluminum salt and circulating liquid, which can be used in S2.

2. The method according to claim 1, characterized in that The particle size of the lepidolite defluorination calcined material is between 200 meshes and 400 meshes.

3. The method according to claim 1, characterized in that The mass content of fluorine in the lepidolite defluorination calcined material is less than or equal to 1.5% based on the mass of the lepidolite defluorination calcined material.

4. The method according to claim 1, characterized in that The first acid solution is a sulfuric acid aqueous solution, and the concentration of the sulfuric acid aqueous solution is 1.5 mol / L to 2.5 mol / L.

5. The method according to claim 1, characterized in that: The acid leaching treatment satisfies at least one of the following conditions: (1) The liquid-to-solid ratio of the first acid solution to the lepidolite defluorination calcined material is (5-10):1; (2) The acid leaching temperature is 60℃~90℃; (3) The acid leaching time is 60 minutes to 120 minutes.

6. The method according to claim 1, characterized in that In S4, the second acid solution is a sulfuric acid aqueous solution, and the concentration of the sulfuric acid aqueous solution is 0.5 mol / L to 2 mol / L.

7. The method according to claim 1, characterized in that: In S4, the liquid-to-solid ratio of the second acid solution to the aluminum benzoate precipitate is (5-10):1; and / or the dissolution time is 60-120 min.

8. The method according to claim 1, characterized in that: In S5, the aluminum-rich solution is cooled to 10°C to 20°C.

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