Lithium recovery water wash solution and method for recovering lithium from lithium-containing waste solution

Abstract

The present invention relates to a method for recovering lithium from a lithium-containing waste liquid, the method including the steps of: filtering a cathode material wash solution to separate solid metals contained in the basic waste liquid; adding sulfuric acid to the cathode material wash solution from which the solid metals have been filtered to acidify it and convert lithium carbonate or lithium hydroxide into lithium sulfate; concentrating the wash solution converted into lithium sulfate to obtain a high-concentration lithium sulfate solution; and mixing the high-concentration lithium sulfate solution with a resultant product obtained by leaching from an ore.

Description

[Technical Field]

[0001] The present invention relates to a method for recovering lithium, and more particularly to a method for recovering lithium from a washing solution for recovering lithium and a lithium-containing waste solution. [Background technology]

[0002] Positive electrode active materials for lithium secondary batteries include materials such as lithium, nickel, cobalt, and manganese. To improve the performance of electric vehicles, increased battery capacity and lifespan are required, leading to increased demand for high-Ni batteries with high energy density. When the Ni content is high, Ni tends to remain divalent, resulting in the production of large amounts of lithium by-products such as LiOH and Li2CO3 on the surface. These lithium by-products must be thoroughly removed by a water washing process, and if they are produced in large quantities on the surface, they can degrade the performance of the lithium battery.

[0003] However, the washing solution generated by the washing process contains lithium along with sulfate, and if the lithium in the washing solution is recovered, it can be used as a raw material for producing lithium hydroxide and lithium carbonate.

[0004] Most of the technologies for recovering lithium from solutions containing lithium relate to solutions obtained by leaching waste batteries with acid, but there are few technologies for the water wash solution generated during the cathode material manufacturing process. Some technologies use a chemical precipitation method to remove impurities such as sulfates, then concentrate the solution to precipitate lithium carbonate in order to recover lithium from lithium-containing waste solution.

[0005] However, the method of recovering lithium by precipitating lithium carbonate in the washing solution has problems in that the deposit adheres to the equipment, which can hinder stable operation of the equipment, and the removal of the deposited deposit can result in a loss of lithium. Furthermore, equipment such as a settling tank or a filter is required to separate the solid phase deposit, which can lead to an increase in capital investment costs.

[0006] In addition, the precipitate contains a large amount of impurities, which requires a purification process to remove them, and the precipitate must be redissolved before being used in the purification process. From the viewpoint of lithium, the lithium is dissolved in the washing solution, becomes a solid phase during precipitation, and must be redissolved, which complicates the process and is uneconomical.

[0007] Therefore, there has been growing interest in a technology for immediately introducing the wastewater into the purification process, but the low concentration of lithium present in the wastewater reduces the process efficiency, leading to a decrease in productivity. In order to efficiently recover lithium from the wastewater, the wastewater must be concentrated to the maximum extent possible to prevent lithium from being precipitated. Summary of the Invention [Problem to be solved by the invention]

[0008] The technical problem to be solved by the present invention is to provide a concentrated washing solution that maximizes lithium concentration during evaporation and does not generate precipitates in order to recover lithium from the lithium-containing washing solution. Another technical problem to be solved by the present invention is to provide a method for recovering lithium from a lithium-containing waste solution, which provides a method for maximizing lithium concentration during evaporation and concentration without generating precipitates in order to recover lithium from a lithium-containing washing solution. [Means for solving the problem]

[0009] The washing solution for recovering lithium according to one embodiment of the present invention is a washing solution produced from a lithium-containing waste solution and can satisfy the following formula 1: [Formula 1] [Li] / ([Na]+[K]+[S])≦0.50 (In the above formula 1, [Li], [Na], [K], and [S] respectively represent the contents [g / L] of Li, Na, K, and S in the washing solution.)

[0010] According to another embodiment of the present invention, a method for recovering lithium from a lithium-containing waste liquid may include the steps of filtering a cathode material wash solution to separate solid metals contained in the basic waste liquid; adding sulfuric acid to the cathode material wash solution from which the solid metals have been filtered to acidify the cathode material wash solution, thereby converting lithium carbonate or lithium hydroxide into lithium sulfate; concentrating the wash solution converted to lithium sulfate to obtain a high-concentration lithium sulfate solution; and mixing the high-concentration lithium sulfate solution with a resultant product obtained by leaching from an ore.

[0011] In one embodiment, the step of mixing the high-concentration lithium sulfate solution with the leached product from the ore may be performed before the step of purifying the leached product. In one embodiment, the step of acidifying the basic water wash solution from which the solid metal has been filtered by adding sulfuric acid to convert lithium carbonate or lithium hydroxide to lithium sulfate may be performed by controlling the pH to 6 or less.

[0012] In one embodiment, in the step of concentrating the washing solution converted to lithium sulfate to obtain a concentrated lithium sulfate solution, the concentrated washing solution may satisfy the following formula 1: [Formula 1] [Li] / ([Na]+[K]+[S])≦0.50 (In the above formula 1, [Li], [Na], [K], and [S] respectively represent the contents [g / L] of Li, Na, K, and S in the washing solution.)

[0013] In one embodiment, the step of concentrating the washing water switched to lithium sulfate to obtain a high-concentration lithium sulfate solution may include concentrating the washing water to half or less of its original mass. In one embodiment, the step of concentrating the washing water switched to lithium sulfate to obtain a high-concentration lithium sulfate solution may include concentrating the washing water to half to one-eighth of its original mass.

[0014] In one embodiment, the step of concentrating the lithium sulfate-converted washing solution to obtain a high-concentration lithium sulfate solution may include controlling the weight percent of a solid phase to 1.0% or less. In one embodiment, the solid phase may be a Li2CO3 precipitate.

[0015] In one embodiment, carbon dioxide may be removed by adding sulfuric acid to the basic washing solution, from which the solid metals have been filtered, to acidify the solution and convert lithium carbonate or lithium hydroxide into lithium sulfate. In one embodiment, the high-concentration lithium sulfate solution obtained by concentrating the washing solution converted to lithium sulfate may have a carbon content reduced by 50% or more compared to the basic washing solution.

[0016] In one embodiment, in the step of adding sulfuric acid to the cathode material washing solution from which the solid metal has been filtered to acidify the solution and convert lithium carbonate or lithium hydroxide into lithium sulfate, the sulfuric acid may be added in an amount of 10 to 15 parts by weight based on 100 parts by weight of the cathode material washing solution. In one embodiment, the method may be a method for recovering lithium components from a cathode material washing solution containing metals including lithium and nickel and sulfates during a process of producing a cathode active material. [Effects of the Invention]

[0017] According to one embodiment of the present invention, the lithium recovery washing solution satisfies a lithium content of 0.5 or less relative to sodium, potassium, and sulfur, thereby maximally concentrating lithium or preventing the generation of precipitates, thereby providing a concentrated washing solution capable of recovering high-concentration lithium.

[0018] In another embodiment of the present invention, a method for recovering lithium from a lithium-containing waste solution is provided, which recovers lithium from the lithium-containing wash solution by adding an acid solution to the wash solution to lower the pH, thereby providing a method for maximizing lithium concentration or preventing the generation of precipitates during evaporation and concentration. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a flowchart of a method for recovering lithium from a lithium-containing waste liquid according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram of a method for recovering lithium from a lithium-containing waste solution according to one embodiment of the present invention. [Figure 3] FIG. 3 is a graph of solid phase fraction by concentration ratio according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] In describing the present invention, terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited to these. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Thus, a first part, component, region, layer, or section described below may also be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0021] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular form includes the plural form unless the context clearly dictates otherwise. As used in the specification, the meaning of "comprising" embodies certain properties, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other properties, regions, integers, steps, operations, elements, and / or components.

[0022] When we say that a part is "on" another part, it means that it is immediately on top of the other part, or that there may be other parts between them. In contrast, when we say that a part is "directly on top" of another part, there are no other parts in between.

[0023] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries are additionally interpreted to have a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted in an ideal or very formal sense unless otherwise defined. Also, unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight.

[0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to exemplary embodiments thereof so that those skilled in the art can easily practice the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments set forth herein.

[0025] FIG. 1 is a flowchart of a method for recovering lithium from a lithium-containing waste liquid according to one embodiment of the present invention. Referring to FIG. 1 , a method for recovering lithium from a lithium-containing waste solution according to one embodiment of the present invention is a method for recovering lithium components from a cathode material wash solution containing sulfate and metals including lithium and nickel during a cathode active material production process, the method including: filtering the cathode material wash solution to separate solid metals contained in the cathode material waste solution (S100); adding sulfuric acid to the cathode material wash solution from which the solid metals have been filtered to acidify it, thereby converting lithium carbonate or lithium hydroxide into lithium sulfate (S200); concentrating the wash solution converted to lithium sulfate to obtain a high-concentration lithium sulfate solution (S300); and mixing the high-concentration lithium sulfate solution with a resultant product leached from ore (S400).

[0026] In the step (S100) of filtering the cathode material washing solution to separate solid metals contained in the cathode material waste solution, the cathode material waste solution may be a waste solution generated during a cathode active material manufacturing process. Specifically, the waste solution refers to a filtered solution obtained by stirring a lithium transition metal oxide in a washing solution after manufacturing the lithium transition metal oxide to reduce by-products, such as lithium by-products present on the surface of the lithium transition metal oxide. More specifically, the waste solution may be a solution containing metals such as nickel, cobalt, or manganese, or containing lithium together with impurities such as nickel or sulfate.

[0027] In one embodiment, the cathode material washing solution may be a basic solution having a pH of 7 to 15, more specifically 10 to 15. This solution may become basic by adding an aqueous solution of NaOH or NH4OH through a coprecipitation reaction during the cathode material manufacturing process.

[0028] In one embodiment, the cathode material washing solution may include lithium hydroxide or lithium carbonate. Specifically, the lithium hydroxide or lithium carbonate may contain several hundred ppm to several thousand ppm of lithium.

[0029] The step of filtering the cathode material washing solution to separate solid metals contained in the cathode material waste solution (S100) may be a step of separating a solid phase of cathode material, e.g., metal oxides, through a filtration process. Specifically, the step may be a step of removing the metal oxides, which are impurities contained in the waste solution in the form of solids. In one embodiment, the solid metals may be oxides containing at least one of nickel, cobalt, and manganese.

[0030] In one embodiment, the filtration process for separating the solid metals may be performed by vacuum filtration using filter paper, and the filter paper may be smaller than the average particle size (D50) of the solid metals. Specifically, the filter paper may have pores of 1 to 5 μm, more specifically, 1 to 3 μm. In this way, metal oxides in the wastewater are filtered through the filter paper, and other components pass through the filter paper, resulting in separation of the solid and liquid phases.

[0031] In the step (S200) of adding sulfuric acid to the cathode material washing solution from which the solid metal has been filtered to acidify it and convert lithium carbonate or lithium hydroxide into lithium sulfate, the cathode material washing solution, which exhibits basicity, can be acidified by adding sulfuric acid to the basic washing solution. Specifically, the acidification of the cathode material washing solution may be such that lithium carbonate and lithium hydroxide contained in the waste solution are converted into lithium sulfate through reactions such as those shown in the following reaction formulas 1 and 2. [Reaction Scheme 1] Li2CO3+H2SO4→Li2SO4+CO2+H2O [Reaction Scheme 2] 2LiOH+H2SO4→Li2SO4+2H2O

[0032] In one embodiment, the step of acidifying the cathode material washing solution from which the solid metal has been filtered by adding sulfuric acid to convert lithium carbonate or lithium hydroxide to lithium sulfate may include the step of removing carbon dioxide. According to Reaction 1, carbon dioxide (CO2) is emitted as a separate gas, and the emitted carbon dioxide can reduce the carbon content in the cathode material washing solution.

[0033] In one embodiment, in the step (S200) of acidifying the basic washing solution obtained by filtering the solid metals by adding sulfuric acid to replace lithium carbonate or lithium hydroxide with lithium sulfate, the acidification may be controlled to a pH of 6 or less. Specifically, the acidification may be controlled to a pH of 5 or less. If the pH is higher than the above range, there is a problem in that lithium carbonate may be precipitated during concentration.

[0034] In one embodiment, in the step (S200) of acidifying the cathode material washing solution from which the solid metal has been filtered by adding sulfuric acid to convert lithium carbonate or lithium hydroxide into lithium sulfate, the sulfuric acid may be added in an amount of 10 to 15 parts by weight based on 100 parts by weight of the cathode material washing solution. Specifically, the sulfuric acid may be added in an amount of 12.0 to 14.5 parts by weight, more specifically, 12.9 to 14.1 parts by weight based on 100 parts by weight of the cathode material washing solution.

[0035] If the sulfuric acid content is outside the upper limit of the above range, there is a problem that the burden of sulfur (S) removal in the purification process increases when the washing water is reused, and if the sulfuric acid content is outside the lower limit of the above range, there is a problem that precipitates are formed during concentration.

[0036] The step (S300) of concentrating the washing solution switched to lithium sulfate to obtain a high-concentration lithium sulfate solution is a step of evaporating the washing solution using an evaporator to obtain a high-concentration lithium sulfate solution. Specifically, in the step of obtaining the high-concentration lithium sulfate solution, the concentration factor can be confirmed by evaporating the washing solution and reducing the mass of the aqueous solution. For example, if the mass of the aqueous solution is reduced by 1 / 2, 1 / 4, 1 / 5, 1 / 8, or 1 / 10, the concentration factor of the aqueous solution may be 2x, 4x, 5x, 8x, or 10x.

[0037] In one embodiment, in the step (S300) of concentrating the washing solution converted to lithium sulfate to obtain a high-concentration lithium sulfate solution, the mass of the washing solution may be concentrated to ½ or less. Specifically, the mass of the washing solution may be concentrated to a range of ½ to ⅛.

[0038] Concentration outside the upper limit of the range may result in excessive solid phase ratio and excessive formation of precipitates, whereas concentration outside the lower limit of the range may result in low lithium yield.

[0039] In one embodiment, the step of concentrating the converted lithium sulfate washing solution to obtain a high-concentration lithium sulfate solution (S300) can control the solid phase ratio to 1.0% or less by weight. The solid phase can be a Li2CO3 precipitate. Specifically, the solid phase ratio can be controlled to 0.56% or less, more specifically, 0.26% or less, and even more specifically, 0.16% or less.

[0040] If the ratio of the solid phase is outside the above range, deposits may adhere to the equipment, hindering stable operation of the equipment, and lithium may be lost when removing the deposited deposits.

[0041] In one embodiment, the step (S300) of concentrating the washing solution that has been converted to lithium sulfate to obtain a highly concentrated lithium sulfate solution may be performed at a temperature in the range of 50 to 90° C. Specifically, the temperature may be in the range of 50 to 80° C., more specifically, in the range of 60 to 80° C. In one embodiment, the step of concentrating the washing solution that has been converted to lithium sulfate to obtain a highly concentrated lithium sulfate solution may be performed at an absolute pressure in the range of 100 to 300 mbar, specifically, in the range of 150 to 250 mbar.

[0042] If the temperature is outside the upper limit of the range, carryover problems may occur. Specifically, if the temperature is too high, the pressure may become too high, resulting in a low lithium recovery rate due to extraction of the lithium-containing solution rather than removal of water alone. If the temperature is outside the lower limit of the range, evaporation and concentration may not be achieved.

[0043] In one embodiment, in the step (S300) of concentrating the washing solution converted to lithium sulfate to obtain a highly concentrated lithium sulfate solution, the concentrated washing solution may satisfy the following Equation 1: [Formula 1] [Li] / ([Na]+[K]+[S])≦0.50 (In the above formula 1, [Li], [Na], [K], and [S] respectively represent the contents [g / L] of Li, Na, K, and S in the washing solution.)

[0044] The above-mentioned formula 1 is a relational expression relating the lithium content to the total amount of impurities, Na, K, and S, in the washing solution that has been switched to lithium sulfate. The formula 1 may be 0.50 or less, specifically 0.40 to 0.50 or less. By satisfying the value of the formula 1, lithium is not precipitated during concentration, and thus a concentrated washing solution with a high lithium content can be obtained, thereby increasing the lithium recovery rate from the waste solution.

[0045] If the concentration is outside the upper limit of the formula 1, lithium deposition may occur during concentration, whereas if the concentration is outside the lower limit of the formula 1, the impurity content may become excessively high.

[0046] The step of mixing the high-concentration lithium sulfate solution with the resultant leached from the ore (S400) may be performed by adding the high-concentration lithium sulfate solution between the leaching process and the primary purification process of a typical lithium ore recovery process. Specifically, the lithium ore recovery process may include a calcination process in which a lithium concentrate or ore is heated at a high temperature to facilitate a reaction between the concentrate or ore and sulfuric acid, a roasting process in which the calcined concentrate or ore is reacted with sulfuric acid to convert lithium ions into lithium sulfate, and a leaching process and purification process in which the lithium sulfate is dissolved in water. By mixing the high-concentration lithium sulfate solution with the leaching process and purification process among the above-mentioned processes, a lithium sulfate solution can be formed as in the conventional method, and lithium present in the water wash can be reused, which is economical and environmentally friendly because no additional equipment is required.

[0047] In one embodiment, the step of mixing the high-concentration lithium sulfate solution with the leached product (S400) may be performed before the step of purifying the leached product. The concentrated lithium sulfate solution prepared from the cathode material aqueous solution is added between the leaching process and the purifying process, and is mixed with the lithium sulfate solution from the leaching process. This has the advantage of allowing the lithium present in the aqueous solution to be reused through an existing lithium ore process.

[0048] According to another embodiment of the present invention, the lithium recovery wash solution refers to a concentrated wash solution produced in the step of concentrating the lithium sulfate-converted wash solution in the lithium recovery method described above, and the lithium recovery wash solution may satisfy the following formula 1: [Formula 1] [Li] / ([Na]+[K]+[S])≦0.50 In the above formula 1, [Li], [Na], [K], and [S] respectively represent the contents of Li, Na, K, and S in the washing solution [g / L].

[0049] The detailed explanation of the formula 1 is the same as that explained with reference to FIG. [Example]

[0050] Specific examples of the present invention will be described below. However, the following examples are merely specific embodiments of the present invention, and the present invention is not limited to the following examples.

[0051] FIG. 2 is a schematic diagram of a method for recovering lithium from a lithium-containing waste solution according to one embodiment of the present invention.

[0052] Referring to FIG. 2, a lithium sulfate solution concentrated in the same manner as in Experimental Examples 1 to 3 below may be added before the primary purification step of the ore Li extraction process.

[0053] Experimental Example 1 - Example 1 0.74 kg of 10% diluted sulfuric acid was added to 5.7 kg of the washing solution to prepare a mixed solution with a pH of 6, and the solution was evaporated using an evaporator at 70°C and an absolute pressure of 200 mbar. Specifically, when the solution was concentrated 2-fold, 4-fold, 5-fold, 8-fold, and 10-fold (mass reductions of 1 / 2, 1 / 4, 1 / 5, 1 / 8, and 1 / 10), the masses of the solution and the precipitated solid phase, as well as the concentrations of Li, Na, K, S, and C in the solution, are shown in Table 1 below.

[0054] At this time, the pH of the washing solution was 12.7, and C was HCO3 - or CO3 2- The washing solution satisfies the following: Li: 4.4 g / L, S: 4.4 g / L, P: 0.009 g / L, K: 0.005 g / L, Na: 0.30 g / L, and C: 1.06 g / L.

[0055] [Table 1]

[0056] From Table 1, it can be seen that the pH of the washing solution was reduced from 12.7 to 6, and the carbon concentration was reduced by approximately 50%, which reduced the amount of Li2CO3 precipitate during concentration. Furthermore, the amount of solid precipitate was controlled to less than 1% of the total weight during 8x concentration. The solid precipitate was mostly Li2CO3.

[0057] Experimental Example 2 - Example 2 0.74 kg of 10% diluted sulfuric acid was added to 5.7 kg of the washing solution to prepare a mixed solution with a pH of 5, and the solution was evaporated using an evaporative concentrator at 70°C and an absolute pressure of 200 mbar. Specifically, when the solution was concentrated 2-fold, 4-fold, 5-fold, 8-fold, and 10-fold (mass reductions of 1 / 2, 1 / 4, 1 / 5, 1 / 8, and 1 / 10), the masses of the solution and the precipitated solid phase, as well as the concentrations of Li, Na, K, S, and C in the solution, are shown in Table 2 below.

[0058] [Table 2]

[0059] Considering Table 2 above, when the pH was lowered to 5, the concentration of C decreased by approximately 70%. Specifically, when the pH was lowered to 5, the solid phase precipitation ratio decreased to 0.16 wt% at an 8-fold concentration.

[0060] Experimental Example 3 - Example 3 0.80 kg of 10% diluted sulfuric acid was added to 5.7 kg of the washing solution to prepare a mixed solution with a pH of 4, and the solution was evaporated using an evaporator at 70°C and an absolute pressure of 200 mbar. Specifically, when the solution was concentrated 2-fold, 4-fold, 5-fold, 8-fold, and 10-fold (mass reductions of 1 / 2, 1 / 4, 1 / 5, 1 / 8, and 1 / 10), the masses of the solution and the precipitated solid phase, as well as the concentrations of Li, Na, K, S, and C in the solution, are shown in Table 3 below.

[0061] [Table 3]

[0062] As can be seen from Table 3, when the pH was lowered to 4, the C concentration decreased by approximately 70%. When the pH was lowered to 4, the solid phase precipitation ratio decreased to 0.17 wt% at an 8-fold concentration.

[0063] Experimental Example 4 - Comparative Example 5.7 kg of the water wash solution was evaporated using an evaporator at 70°C and an absolute pressure of 200 mbar. When the solution was concentrated 2-fold, 4-fold, 5-fold, 8-fold, and 10-fold (mass reductions of 1 / 2, 1 / 4, 1 / 8, and 1 / 10), the masses of the solution and the precipitated solid phase, as well as the concentrations of Li, Na, K, S, and C in the solution, are shown in Table 4 below.

[0064] [Table 4]

[0065] From Table 4, it was found that even at a concentration of 2x, Li2CO3 precipitates were generated at a rate of 1 wt% or more relative to the total weight. Figure 3 is a graph showing the solid phase ratio as a function of the concentration ratio according to one embodiment of the present invention.

[0066] 3, it was confirmed that the solid phase lithium carbonate production rate depending on the concentration ratio can be formed within 1 wt%. Specifically, when the pH is lowered to 6 or less, it was confirmed that the solid phase lithium carbonate production rate is within 1 wt% and it is possible to concentrate the solution 8 times as much as the washing solution.

[0067] The present invention is not limited to the above-described embodiments and / or examples, and can be manufactured in various different forms, and a person skilled in the art to which the present invention pertains should understand that the present invention can be embodied in other specific forms without changing the technical spirit or essential characteristics of the present invention. Therefore, the above-described embodiments and / or examples should be understood to be illustrative in all respects and not limiting.

Claims

1. filtering the cathode material washing solution to separate solid metals contained in the basic waste solution; adding sulfuric acid to the cathode material washing solution from which the solid metal has been filtered to acidify the solution, thereby converting lithium carbonate or lithium hydroxide into lithium sulfate; concentrating the lithium sulfate-switched water wash solution to obtain a concentrated lithium sulfate solution; and 1. A method for recovering lithium from a lithium-bearing waste solution, comprising the step of mixing said concentrated lithium sulfate solution with leached products from an ore.

2. 2. The method for recovering lithium from a lithium-containing waste solution according to claim 1, wherein the step of mixing the highly concentrated lithium sulfate solution with the leached product from the ore is carried out before the step of purifying the leached product.

3. 2. The method for recovering lithium from a lithium-containing waste solution according to claim 1, wherein the step of adding sulfuric acid to the basic washing solution obtained by filtering the solid metal to acidify the basic washing solution and converting lithium carbonate or lithium hydroxide into lithium sulfate comprises controlling the pH of the acidification to 6 or less.

4. 2. The method for recovering lithium from a lithium-containing waste solution according to claim 1, wherein in the step of concentrating the washing solution that has been converted to lithium sulfate to obtain a highly concentrated lithium sulfate solution, the concentrated washing solution satisfies the following formula 1: [Formula 1] [Li] / ([Na]+[K]+[S])≦0.50 (In the above formula 1, [Li], [Na], [K], and [S] respectively represent the contents [g / L] of Li, Na, K, and S in the washing solution.)

5. 2. The method for recovering lithium from a lithium-containing waste solution according to claim 1, wherein the step of concentrating the washing solution that has been converted to lithium sulfate to obtain a high-concentration lithium sulfate solution comprises concentrating the washing solution to a mass of ½ or less.

6. 2. The method for recovering lithium from a lithium-containing waste solution according to claim 1, wherein the step of concentrating the washing solution that has been converted to lithium sulfate to obtain a highly concentrated lithium sulfate solution comprises concentrating the washing solution to a mass in the range of ½ to ⅛.

7. 2. The method for recovering lithium from a lithium-containing waste solution according to claim 1, wherein the step of concentrating the washing solution that has been converted to lithium sulfate to obtain a high-concentration lithium sulfate solution controls a ratio of a solid phase in terms of weight percent to 1.0% or less.

8. The solid phase is Li ２ CO ３ The method for recovering lithium from a lithium-containing waste liquid according to claim 7, wherein the lithium is in the form of a precipitate.

9. 2. The method for recovering lithium from a lithium-containing waste solution according to claim 1, wherein carbon dioxide is removed by a step of adding sulfuric acid to the basic water washing solution obtained by filtering the solid metal to acidify the basic water washing solution and converting lithium carbonate or lithium hydroxide into lithium sulfate.

10. 2. The method for recovering lithium from a lithium-containing waste solution according to claim 1, wherein the high-concentration lithium sulfate solution obtained from the step of concentrating the aqueous washing solution that has been converted to lithium sulfate has a carbon content reduced by 50% or more compared to that of the basic aqueous washing solution.

11. 2. The method for recovering lithium from a lithium-containing waste solution according to claim 1, wherein in the step of adding sulfuric acid to the cathode material washing solution from which the solid metal has been filtered to acidify the cathode material washing solution and convert lithium carbonate or lithium hydroxide into lithium sulfate, the sulfuric acid is added in an amount of 10 to 15 parts by weight based on 100 parts by weight of the cathode material washing solution.

12. 2. The method for recovering lithium from a lithium-containing waste solution according to claim 1, wherein the method is a method for recovering lithium components from a cathode material washing solution containing lithium, nickel, and sulfates during a cathode active material production process.

13. A washing solution produced from a lithium-containing waste solution, A washing solution for recovering lithium that satisfies the following formula 1: [Formula 1] [Li] / ([Na]+[K]+[S])≦0.50 (In the above formula 1, [Li], [Na], [K], and [S] respectively represent the contents [g / L] of Li, Na, K, and S in the washing solution.)

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