Method for pre-recovering lithium from waste cathode materials

Abstract

The present invention relates to a method for recovering lithium from a waste battery cathode material. According to one embodiment, the invention provides a lithium recovery method comprising: a leaching step in which an aqueous solution of an inorganic acid is introduced into a cathode material powder to leach out a metal component including lithium; a precipitation step in which a sodium hydroxide solution is introduced into the leaching solution produced in the leaching step to precipitate a metal component excluding lithium; and a step in which a carbonate is introduced into the lithium leaching solution produced in the precipitation step to produce lithium carbonate.

Description

Technology Field

[0001] The present invention relates to lithium recovery, and more specifically, to a method for recovering lithium from waste cathode material of spent lithium secondary batteries at a low energy cost. Background Technology

[0002] The demand for lithium-ion rechargeable batteries is expected to grow by more than 30% annually due to the expansion of markets for IT, electric vehicles, and energy storage devices. Consequently, the demand for cathode materials, which are key components of rechargeable batteries, is also expected to increase proportionally. However, key cathode materials such as lithium, cobalt, and nickel are rare metals with limited reserves and restricted production regions, leading to significant price fluctuations. Recently, prices have been skyrocketing due to increased demand, and in the case of lithium, this is particularly severe. Therefore, it is a raw material for which there is a great need for resource recycling, specifically by recovering and utilizing lithium from rechargeable battery scrap.

[0003] Conventionally, for lithium recovery, a process is generally used in which nickel, cobalt, manganese, etc., are recovered from the remaining waste liquid after leaching cathode material scrap powder recovered from spent secondary batteries using an inorganic acid. However, the lithium content in the residual waste liquid is approximately 1,000 ppm to 2,000 ppm, which is too low for direct lithium recovery. Therefore, the general method involves increasing the lithium content through methods such as concentration and then adding a carbonation source, such as sodium carbonate or carbon dioxide, to recover the lithium as lithium carbonate. However, this method is a process that requires a large amount of energy to concentrate the lithium and remove sodium sulfate, an impurity in the solution.

[0004] Recently, methods for selectively leaching, concentrating, and crystallizing only lithium have been proposed. Representative methods include reducing spent cathode material with carbon or similar substances to convert the lithium within the cathode material into lithium carbonate (Li2CO3) and then selectively leaching and concentrating only the lithium into water to crystallize it, as well as methods for obtaining lithium hydroxide by oxidizing the lithium within the cathode material using hydrogen or a hydrogen / nitrogen mixed gas and then leaching it into water.

[0005] However, while these methods can obtain high-purity lithium carbonate or lithium hydroxide by selectively leaching only lithium, they require expensive heat treatment furnaces to heat-treat the spent cathode powder and require a large amount of energy for the heat treatment. Prior art literature

[0006] Patent Document 1: Korean Published Patent No. 2011-0117024 (Published October 26, 2011) Patent Document 2: Korean Registered Patent No. 10-1839460 (Published March 16, 2018) The problem to be solved

[0007] The present invention aims to solve the problems of the prior art described above and provides a method for recovering lithium from the cathode material of spent lithium secondary batteries at a low energy cost. means of solving the problem

[0008] According to one embodiment of the present invention, a method for recovering lithium from a waste battery cathode material is provided, comprising: a leaching step of leaching a metal component including lithium by adding an aqueous solution of an inorganic acid to a cathode material powder; a precipitation step of precipitating a metal component excluding lithium by adding a sodium hydroxide solution to the leaching solution generated in the leaching step; and a step of generating lithium carbonate by adding a carbonate to the lithium leaching solution generated in the precipitation step. Effects of the invention

[0009] According to one embodiment of the present invention, lithium can be recovered by completely precipitating and removing valuable metals such as nickel, cobalt, and manganese as hydroxides from a leaching solution with adjusted lithium concentration, and then crystallizing the lithium directly from the high-concentration lithium filtrate through a carbonation reaction. This provides the advantage of effectively recovering lithium without the energy costs for lithium concentration or heat treatment. Brief explanation of the drawing

[0010] FIG. 1 is a flowchart of a lithium recovery method according to one embodiment of the present invention. Specific details for implementing the invention

[0011] The above objects, other objects, features, and advantages of the present invention will be easily understood through the following preferred embodiments associated with the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosed content is thorough and complete and to ensure that the spirit of the invention is sufficiently conveyed to those skilled in the art.

[0012] Where terms such as "first," "second," etc. are used in this specification to describe components, these components shall not be limited by such terms. These terms are used merely to distinguish one component from another. The embodiments described and illustrated herein also include complementary embodiments.

[0013] In this specification, the singular form includes the plural form unless specifically stated otherwise in the text. Expressions used in this specification such as “comprising,” “consisting of,” and “consisting of” do not exclude the presence or addition of one or more other components in addition to the mentioned components.

[0014] The present invention will be described in detail below with reference to the drawings. In describing the specific embodiments below, various specific details have been included to explain the invention more specifically and to aid in understanding. However, a reader with sufficient knowledge in the art to understand the invention will recognize that it can be used without these various specific details. In some cases, it is noted in advance that commonly known parts that are not significantly related to the invention have been omitted to prevent confusion in describing the invention.

[0015] The present invention does not use the conventional process of leaching waste cathode materials in an inorganic acid such as sulfuric acid to recover valuable metals such as nickel, cobalt, and manganese, and then concentrating a low-concentration lithium waste solution to recover lithium; instead, it uses a method in which valuable metals such as nickel, cobalt, and manganese are removed as hydroxides from a leaching solution in which the lithium concentration in the waste cathode material leaching solution has been adjusted, and lithium is directly crystallized from a high-concentration lithium filtrate through a carbonation reaction.

[0016] In this process of obtaining a high-concentration lithium filtrate, if other metals are completely leached and precipitated as hydroxides, there is a problem where work efficiency decreases due to poor filtration properties caused by increased viscosity from the hydroxides. Therefore, by adjusting the amount of inorganic acid acting as a leaching agent to leach out most of the lithium while leaching out other metals minimally, conditions are established to minimize the amount of metal hydroxide precipitates, thereby providing a method to effectively recover lithium without incurring energy costs for concentration or heat treatment.

[0017] FIG. 1 is a flowchart of a lithium recovery method according to an embodiment of the present invention. Referring to FIG. 1, the lithium recovery method according to an embodiment may include the steps of: introducing an aqueous solution of inorganic acid into the cathode material powder of a waste battery to leach out a metal component including lithium (S10); filtering the leachate to remove residue (S20); introducing sodium hydroxide into the leachate to precipitate a metal component excluding lithium as a hydroxide (S30); filtering the reaction product generated in the precipitation step to separate it into a lithium leachate and a nickel-cobalt-manganese (NCM) cake (S40); and introducing a carbonate into the lithium leachate to produce lithium carbonate (S50).

[0018] In addition, in one embodiment, a step (S60) of washing the residue separated in step (S20) and the NCM cake separated in step (S40) and a step (S70) of recovering nickel, cobalt, and manganese from the washing step (S60) may be additionally performed, and the washing solution from the washing step (S60) may be sent back to step (S10) to perform the lithium recovery process again.

[0019] We will explain each step in more detail.

[0020] In the first step (S10), the cathode material powder of the waste secondary battery is introduced into an aqueous solution of inorganic acid to leach out metal components including lithium. For example, at least one of sulfuric acid, hydrochloric acid, and nitric acid may be used as the inorganic acid. However, since sulfates are used as precursor raw materials for manufacturing cathode materials, it may be preferable to use sulfuric acid as the inorganic acid in this case.

[0021] The amount of inorganic acid added to the cathode material powder is sufficient to adequately leach lithium; however, if the amount is excessive, the leaching rate of non-lithium metallic components such as nickel, cobalt, and manganese increases, leading to the formation of a large amount of hydroxide cake during the subsequent neutralization reaction, which reduces filtration efficiency. Therefore, it is desirable to ensure that the weight ratio of the inorganic acid to the cathode material powder is between 0.5 and 2, that is, that the inorganic acid is approximately 0.5 to 2 times the weight ratio of the cathode active material powder, so that less than 50% of the total metallic components are leached. Additionally, hydrogen peroxide, which is generally used as a reducing agent for the complete leaching of the cathode active material, is not used.

[0022] The solid-liquid ratio during leaching is very important as it determines the lithium concentration in the leaching solution for recovering lithium without concentration. Although there is no limit on the lithium concentration in the leaching solution, it is desirable to adjust the solid-liquid ratio so that the lithium concentration is between 5,000 ppm and 15,000 ppm in order to recover lithium without an additional concentration process. If the lithium concentration in the lithium leaching solution is 5,000 ppm or less, a concentration process becomes necessary, and if it is 15,000 ppm or more, the viscosity increases during the subsequent neutralization reaction and filtration steps, making it difficult to separate the solid and liquid phases. Therefore, in one embodiment, to adjust the lithium concentration in the lithium leaching solution to be between 5,000 ppm and 15,000 ppm, it is desirable that the solid-liquid ratio of the cathode material powder and the aqueous inorganic acid solution (i.e., the weight ratio of the solid cathode material powder and the solution phase, such as sulfuric acid and water) be between 5.0 and 15.0.

[0023] In step (S10), the metal components are leached by reacting the cathode material powder with an aqueous solution of inorganic acid, and then in step (S20), the leached solution is filtered to remove residues, and then in step (S30), a sodium hydroxide (NaOH) solution is added to the leached solution to precipitate the metal components excluding lithium. In this step (S30), sodium hydroxide is added to neutralize the pH of the leached solution to 9 or higher, preferably between pH 10 and 12, and the solution is reacted for several hours to precipitate the valuable metal components excluding lithium as a hydroxide.

[0024] Subsequently, in step (S40), the reactant from step (S30) is filtered to recover valuable metals such as nickel-cobalt-manganese (NCM) in the form of a cake, and the lithium leaching solution containing lithium is separated as a filtrate.

[0025] The separated lithium leaching solution contains lithium concentrated to a high concentration of 5,000 ppm to 15,000 ppm, and lithium can be recovered by adding a carbonate to the lithium leaching solution in step (50) to produce lithium carbonate. Any carbonate that forms lithium carbonate can be added, but carbon dioxide or sodium carbonate is generally effective. When carbon dioxide is used, there is no additional sodium incorporation, so it is effective in lowering the sodium content of the final product, but sodium carbonate is more effective in terms of reactivity for forming lithium carbonate.

[0026] The amount of carbonate added is appropriate if it is at least 1:1 of the theoretical equivalent to form lithium carbonate, and for the optimal reaction, it is effective to add an excess of about 5% to 50% of carbonate, and anything more than that is not economically desirable.

[0027] The lithium carbonate produced in step (S50) can be washed with hot water to remove sodium and sulfur components remaining in the lithium carbonate crystals. Since the solubility of lithium carbonate decreases at high temperatures, it is desirable to use high-temperature washing water. If necessary, washing three or more times is possible, but since lithium is lost during washing, washing twice is appropriate.

[0028] The lithium content in the waste liquid and lithium carbonate wash water generated after lithium recovery in step (S50) is about 2,000 ppm, and it can be recovered as lithium carbonate through a carbonation reaction after the concentration process.

[0029] Meanwhile, the hydroxide cake separated in the filtration step (S40) can also be washed (step S60) and a subsequent process (step S70) for recovering valuable metals can be performed. That is, the hydroxide cake is washed so that the solid portion is recovered through a valuable metal recovery process, and the washing water containing lithium is supplied to step (S10) to be reused in the leaching process of the spent cathode material. At this time, the residue obtained in the filtration step (S20) and the hydroxide cake separated in the filtration step (S40) can be combined, washed (step S60), and a subsequent process (step S70) for recovering valuable metals can also be performed.

[0031] Experimental Example

[0032] Specific experimental examples according to the lithium recovery method of the present invention described above will be explained below.

[0033] Steps S10 and S20: 100g of 98% sulfuric acid and 235g of water were added to 67g of spent cathode material, and after leaching at 70°C for 4 hours, solid-liquid separation was performed to obtain 345g of leachate. The components of the spent cathode material and the leachate are as shown in Tables 1 and 2 below, respectively.

[0034] Results of component analysis of waste cathode material Li Ni Co Mn Waste cathode material (%) 7.03 35.24 11.10 10.92

[0035] Results of component analysis of the leachate Li Ni Co Mn Total leachate (%) 1.26 3.49 0.7 0

[0036] Steps S30 and S40: 50% sodium hydroxide was added to 345g of the leachate to adjust the pH to 10, and after reacting for 4 hours, the mixture was filtered to separate it into a lithium leachate and a cake of other metal hydroxides. The composition of the separated lithium leachate is shown in Table 3 below.

[0037] Component analysis results of the separated lithium leaching solution Li Ni Co Mn Lithium leaching solution (ppm) 11,000 <1 <1 <1

[0038] As can be seen in Table 3, the lithium content in the lithium leaching solution is 11,000 ppm, which is 5,000 ppm or higher, so a subsequent concentration process is not required.

[0039] Step S50: The separated lithium leachate was placed in a reaction vessel maintained at 80 degrees Celsius, and while stirring, a 25% diluted sodium carbonate solution was added to the lithium carbonate in an amount exceeding 30% of the theoretical equivalent. After reacting for 1 hour, the mixture was filtered to obtain lithium carbonate crystals. Subsequently, the recovered lithium carbonate was washed twice with hot water and dried to recover the lithium carbonate. The analysis results of the recovered lithium carbonate are shown in Table 4 below.

[0040] Analysis results of recovered lithium carbonate (Unit: ppm) Li Ni Co Mn Fe Al Cu Na Mg K 18,500 6.4 ND ND 2.6 ND ND 790 3.7 3.5

[0041] Although the present invention has been described above with reference to limited embodiments and drawings, the present invention is not limited to the above embodiments. Those skilled in the art will understand that various modifications and variations are possible from the description above. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the claims set forth below as well as equivalents thereof.

Claims

Claim 1 A method for recovering lithium from a waste battery cathode material, comprising: a leaching step (S10) in which an aqueous solution of an inorganic acid is introduced into cathode material powder to leach out metal components including lithium; a precipitation step (S30) in which a sodium hydroxide solution is introduced into the leachate produced in the leaching step to precipitate metal components excluding lithium; a step (S40) in which a reaction product produced in the precipitation step is filtered to separate it into a lithium leachate and a nickel-cobalt-manganese (NCM) cake; and a step (S50) in which a carbonate is introduced into the lithium leachate separated in the separation step (S40) to produce lithium carbonate; wherein, in the leaching step (S10), the lithium concentration in the lithium leachate separated in the separation step (S40) is between 5,000 ppm and 15,000 ppm, and the weight ratio of the inorganic acid to the cathode material powder is between 0.5 and 2, and the solid-liquid ratio of the cathode material powder to the aqueous solution of the inorganic acid is between 5 and 15. Claim 2 A lithium recovery method according to claim 1, further comprising the step of washing the hydroxide cake generated in the precipitation step (S30) and recovering valuable metals. Claim 3 A lithium recovery method according to claim 1, characterized in that the inorganic acid aqueous solution is an aqueous sulfuric acid solution. Claim 4 delete Claim 5 delete

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