Method for extracting lithium from lithium-containing clay

Abstract

The present disclosure relates to a method for recovering lithium from clay, the method comprising the steps of: (S1) heat-treating a mixture of lithium-containing clay and calcium sulfate (CaSO4) to prepare a sintered product; (S2) leaching the sintered product with water to prepare a water-leached product; and (S3) subjecting the water-leached product to solid-liquid separation into a lithium-containing solution and a residue.

Description

Method for extracting lithium from lithium-containing clay

[0001] The present disclosure relates to a method for extracting lithium from lithium-containing clay.

[0002] As the demand for small home appliances, IT devices, electric vehicles (EVs), and energy storage systems (ESS) increases rapidly, the demand for lithium-ion batteries, characterized by their lightweight nature, high energy density, and high capacity, is also rising sharply. Since the cathode materials and electrolytes of lithium-ion batteries contain large amounts of lithium, research is underway to extract lithium contained in minerals at high concentrations and purity to meet the high demand for lithium.

[0003] Among them, since the lithium contained in clay accounts for 7% of the total lithium reserves, it is essential to develop a method to recover the lithium contained in clay in order to secure lithium. Conventionally, an acid leaching method has been developed to recover lithium from clay by mixing an acid, such as sulfuric acid (H2SO4), with the clay to leach the lithium. However, during acid leaching, impurities such as calcium, magnesium, and iron are leached along with the lithium, making it impossible to recover high-purity lithium, and there is a problem that the process becomes complicated as an additional impurity removal process is required.

[0004] In addition, there is a disadvantage in that acid usage is very high in order to improve the low lithium leaching efficiency. Therefore, a beneficiation process is essential to recover concentrate with a high lithium concentration by removing gangue from the clay using wet sieving, wet cyclones, etc., before performing acid leaching. However, even if a beneficiation process is performed to remove impurities from the clay in advance, acid usage still accounts for more than 50% of the clay weight, and there are limitations in obtaining high-purity lithium.

[0005] Furthermore, due to the inherent characteristics of clay, the solid-liquid separation efficiency is very low, leading to a problem of reduced lithium recovery rates. Since the purity of lithium recovered through acid leaching is low and solid-liquid separation is difficult, the solvent must be evaporated to concentrate the lithium. However, not only is the evaporation process required to incur additional costs, but impurities leached out along with lithium during the process precipitate in a solid state. Consequently, scale—a solid impurity—accumulates in reactors and piping, causing blockages and poor flow. This leads to problems with process equipment and incurs additional process costs to resolve them, resulting in reduced economic viability.

[0006] Accordingly, there is a need for a method to obtain high-purity lithium with a high recovery rate by improving solid-liquid separation performance through the selective leaching of lithium contained in clay while simultaneously effectively removing impurities.

[0007] The purpose of the present disclosure is to solve the problems of the prior art described above by providing a method capable of recovering high-purity lithium with a high recovery rate by effectively removing impurities and selectively leaching lithium contained in clay.

[0008] Another objective of the present disclosure is to provide a method for recovering lithium at a low cost and simplifying the process by enabling the recovery of high-purity lithium without pre-treating the clay before recovery or without a separate impurity removal process when recovering lithium from the clay.

[0009] A lithium recovery method according to the present disclosure comprises: (S1) a step of preparing a calcined product by heat-treating a mixture of lithium-containing clay and calcium sulfate (CaSO4); (S2) a step of preparing a water-leached product by water-leaching the calcined product; and (S3) a step of separating the water-leached product into a lithium-containing solution and a residue.

[0010] In one example, the mixture may contain 1 to 50 parts by weight of calcium sulfate (CaSO4) based on 100 parts by weight of lithium-containing clay.

[0011] In one example, after step (S3) above, (S4) a step of recovering residual lithium contained in the residue may be further included.

[0012] In one example, the above step (S4) may be performed two or more times.

[0013] In one example, the above step (S4) can be performed by a countercurrent washing (CCW) method.

[0014] In one example, after step (S4), the method may further include step (S5) of mixing the residual lithium with the lithium-containing solution to recover a concentrated lithium-containing solution.

[0015] In one example, the lithium-containing clay may contain less than 5,000 mg / kg of lithium.

[0016] In one example, lithium may be selectively leached in step (S2).

[0017] In one example, the firing of step (S1) above may be performed under temperature conditions of 800 to 1200 ℃.

[0018] In one example, the step of crushing the calcined material after step (S1) and before step (S2) may be further included.

[0019] In one example, the leaching rate of impurities represented by Formula 1 below may be less than 5%.

[0020] [Equation 1]

[0021] Leaching rate (%) = (w s / w c ) X 100

[0022] (In Equation 1 above, w s represents the weight of impurities contained in the lithium-containing solution, and w c ) refers to the weight of impurities contained in the clay.

[0023] In one example, the above (S2) step may be performed under a temperature condition of 40 to 100 ℃.

[0024] In one example, the lithium recovery rate can be 98% or higher.

[0025] In one example, in step (S1), a water-soluble compound containing lithium and an insoluble compound containing calcium and magnesium may be produced.

[0026] In one example, the insoluble compound may include calcium magnesium silicate.

[0027] The lithium recovery method according to the present disclosure can recover high-purity lithium with a high recovery rate by effectively removing impurities contained in clay and selectively leaching lithium at the same time.

[0028] In addition, since no additional impurity removal process is required before pre-treating the clay or during or after lithium recovery, the process can be simplified and process costs can be reduced.

[0029] Furthermore, it has the advantage of effectively concentrating lithium without evaporating the solvent.

[0030] FIG. 1 is a flowchart illustrating a lithium recovery method according to one embodiment of the present disclosure.

[0031] Figures 2 to 4 are X-ray diffraction (XRD) spectra of the clay, calcined product, and water leaching product of Example 1, respectively.

[0032] The terms used in this specification have been selected to be as widely used as possible, taking into account the function of this disclosure; however, these terms may vary depending on the intent of those skilled in the relevant field, case law, the emergence of new technologies, etc. Unless otherwise defined, technical and scientific terms used may have the meaning commonly understood by those skilled in the art to which this invention pertains.

[0033] In this specification and the appended claims, terms such as “comprising” or “having” mean that the features or components described in the specification exist, and unless specifically limited, do not preclude the possibility that one or more other features or components may be added.

[0034] In this specification and the appended claims, terms such as "first," "second," etc. are used not in a limiting sense, but for the purpose of distinguishing one component from another.

[0035] Singular expressions used in this specification and the appended claims include plural expressions unless the context clearly indicates that they are singular. Additionally, plural expressions include singular expressions unless the context clearly indicates that they are plural.

[0036] Additionally, numerical ranges used herein include lower and upper limits and all values ​​within the range, increments logically derived from the form and width of the defined range, all of which are limited values, and all possible combinations of upper and lower limits of numerical ranges defined in different forms. Unless otherwise specifically defined in the specification of this disclosure, values ​​outside the numerical range that may occur due to experimental error or rounding of values ​​are also included in the defined numerical range.

[0037] Terms such as "approximately" used in this specification and the appended claims are used to encompass tolerances when tolerances exist.

[0038] The term “impurity” as used in this specification may include one or more selected from calcium, magnesium, iron, chromium, zinc, manganese, aluminum, titanium, and boron based on elemental composition, and as an example, in this specification, “impurity” may include one or more selected from calcium, magnesium, and iron based on elemental composition.

[0039] As used in this specification, the terms “lithium recovery rate” and “lithium leaching rate” may refer to the weight of lithium contained in a lithium-containing solution relative to the weight of lithium contained in clay.

[0040] Hereinafter, a method for recovering lithium from clay according to the present disclosure will be described in detail.

[0041] Referring to FIG. 1, the lithium recovery method according to the present disclosure comprises: (S1) a step of heat-treating a mixture of lithium-containing clay and calcium sulfate (CaSO4) to produce a calcined product; (S2) a step of leaching the calcined product with water to produce a water-leached product; and (S3) a step of separating the water-leached product into a lithium-containing solution and a residue.

[0042] By mixing lithium-containing clay with calcium sulfate and heat-treating it to produce a calcined product, followed by a series of steps involving water leaching, impurities such as Ca, Mg, and Fe contained in the clay can be removed, and lithium can be selectively leached. This resolves the problem of difficulty in solid-liquid separation due to the inherent characteristics of clay, thereby significantly improving the separation efficiency and consequently significantly enhancing the lithium recovery rate. Furthermore, by minimizing the leaching of impurities, selective recovery of lithium is possible, and the purity of the recovered lithium can be significantly improved.

[0043] In one example, in step (S1), lithium-containing clay and calcium sulfate may react to form a lithium-containing water-soluble compound and an insoluble compound.

[0044] The insoluble compounds include calcium magnesium silicate, such as Ca2MgSiO7, CaMgSi2O6, etc. As calcium (Ca) and magnesium (Mg), which are major impurities contained in lithium-containing clay, are converted into insoluble compounds in step (S1), calcium and magnesium are separated and easily removed without being leached together with lithium in the subsequent step (S2).

[0045] At the same time, as a water-soluble compound containing lithium is formed in step (S1), lithium can be selectively and easily leached into water during water leaching in step (S2). Therefore, since most of the lithium contained in the clay is leached out during the water leaching step, the lithium recovery rate can be significantly improved.

[0046] In one example, the lithium-containing clay may contain lithium in an amount of less than 5000 mg / kg, less than 4000 mg / kg, or less than 3000 mg / kg, and, without limitation, 10 mg / kg or more, 30 mg / kg or more, or 50 mg / kg or more.

[0047] Even though the lithium-containing clay contains predominantly impurities such as calcium and magnesium and relatively little lithium, as the impurities are selectively converted into insoluble compounds in step (S1), most of the impurities can be easily removed through subsequent processes, and lithium can be recovered with high selectivity to recover high-purity lithium.

[0048] In one example, the amount of calcium sulfate added in step (S1) above is not particularly limited as long as the purpose of the present disclosure is achieved, but, for example, based on 100 parts by weight of lithium-containing clay, calcium sulfate (CaSO4) may be contained in an amount of 1 part by weight or more, 3 parts by weight or more, 5 parts by weight or more, 6 parts by weight or more, 7 parts by weight or more, or 8 parts by weight or more, and as an upper limit, may be 50 parts by weight or less, 40 parts by weight or less, 30 parts by weight or less, 20 parts by weight or less, or 15 parts by weight or less, and may be a range between any two of the above values. There is an advantage that even if a small amount of calcium sulfate is added relative to the clay, it has an excellent effect of removing impurities.

[0049] In one example, the calcination of step (S1) may be at 800°C or higher, 850°C or higher, 900°C or higher, 950°C or higher, or 1000°C or higher, and the upper limit may be 1200°C or lower, 1150°C or lower, or 1100°C or lower, and may be a range between any two of the above values. Additionally, step (S1) may be performed for 0.2 to 2 hours, 0.5 to 1.6 hours, or 0.8 to 1.2 hours. Under the above conditions, impurities in the clay and calcium sulfate may effectively react to form an insoluble compound.

[0050] The method may further include a step of crushing the calcined material after step (S1) and before step (S2). Crushing the calcined material reduces the particle size and increases the surface area, thereby increasing the contact area between water and the calcined material in step (S2). Accordingly, when performing step (S2) described later, a larger amount of lithium can be leached out more quickly, thereby improving the lithium recovery rate.

[0051] The above step (S2) is a step of leaching water by introducing water into the pulverized calcined material, wherein the insoluble compounds formed in the above step (S1) are not leached, and lithium can be selectively leached. Since most impurities are removed by water leaching alone without the need for an additional separate impurity removal process, high-purity lithium can be recovered, and the lithium recovery process can be simplified.

[0052] In one example, the above step (S2) may be performed under temperature conditions of 0°C to 100°C, preferably under temperature conditions of 40°C or higher, 50°C or higher, or 60°C or higher, and upper limit may be performed at 100°C or lower, 90°C or lower, or 80°C or lower, and may be a range between any two of the above values. More preferably, it is preferred to perform leaching between 40°C and 80°C, and lithium leaching efficiency may be improved in the above temperature range. In addition, the above step (S2) may be performed for 0.2 to 2 hours, 0.5 to 1.6 hours, or 0.8 to 1.2 hours.

[0053] The above step (S3) is a step of recovering lithium by separating the above water leaching product into a lithium-containing solution and a residue. The lithium-containing solution, which is generated when lithium is dissolved in water during water leaching, and the residue, which contains insoluble compounds that are not dissolved in water, can be separated through solid-liquid separation.

[0054] As described above, due to the characteristics of clay, the solid-liquid separation efficiency is severely reduced in a slurry state mixed with water. However, when lithium contained in clay is recovered by the method according to the present disclosure, the calcium sulfate reacts with the clay to form an insoluble compound in advance, so lithium can be selectively dissolved in water even during water leaching, thereby significantly improving the solid-liquid separation efficiency.

[0055] Such solid-liquid separation can be achieved using any means applicable in the industry without limitation, such as centrifugation, centrifugal dehydration, pressure filtration, vacuum filtration, and suction filtration.

[0056] As a non-limiting example, the lithium-containing solution obtained in step (S3) above can be recovered in step (S2) and subjected to water leaching. By recovering the lithium-containing solution in step (S2) and repeating the water leaching multiple times, insoluble compounds remaining in the lithium-containing solution can be effectively removed.

[0057] When lithium contained in clay is recovered by the method according to the present disclosure, a high-concentration and high-purity lithium-containing solution with a high lithium concentration and significantly low impurity content can be recovered. The recovered lithium-containing solution can be used to produce a high-purity lithium compound, for example, high-purity lithium hydroxide (LiOH), through a lithium compound manufacturing process conventionally performed in the art.

[0058] After the above step (S3), the method may further include (S4) a step of recovering residual lithium contained in the residue; and (S5) a step of mixing the residual lithium with the lithium-containing solution to recover a concentrated lithium-containing solution.

[0059] By recovering the residual lithium remaining in the residue recovered in step (S3) and mixing it with the lithium-containing solution separated in step (S3), a concentrated lithium-containing solution with an improved lithium concentration can be recovered.

[0060] Specifically, the above step (S4) can be performed using a countercurrent washing (CCW) method. Through the countercurrent washing process, residual lithium contained in the residue can be recovered, allowing the lithium to be concentrated quickly and simply.

[0061] The above backflow cleaning can be performed by continuously supplying and discharging residue and water to a cleaning unit, and preferably, backflow cleaning can be performed using a plurality of cleaning units connected in series. For example, when n cleaning units are connected in series, residue can be continuously supplied to the first cleaning unit so as to pass sequentially through the first to nth cleaning units connected in series, and at the same time, water can be continuously supplied to the nth cleaning unit so as to flow in the opposite direction to the flow of residue, thereby recovering a solution containing residual lithium. The cleaning units may be connected in series in numbers of 1 to 30, 2 to 20, or 3 to 10, but the present disclosure is not limited by the number of cleaning units.

[0062] Accordingly, lithium can be concentrated using a small amount of water without an evaporation process, and the lithium recovery rate can be improved by recovering even the lithium remaining in the residue that was not leached out. In addition, this can resolve the problem of blockage or flow failure in reactors and piping caused by impurities remaining in the lithium-containing solution precipitating in a solid state during the conventional evaporation process for lithium concentration.

[0063] Through the above step (S4), more than 90%, more than 95%, or more than 99% of the residual lithium contained in the residue can be recovered, and advantageously, the residual lithium contained in the residue can be fully recovered.

[0064] The above step (S4) may be repeated at least 2 times, at least 3 times, at least 4 times, or at least 5 times, and at an upper limit may be repeated at least 10 times, at least 9 times, or at least 8 times, and may be a range between any two of the above values. The above range is preferred as it allows for the recovery of as much residual lithium as possible, but the present disclosure is not limited thereto.

[0065] When lithium is recovered from clay by the method described above, a significantly high lithium recovery rate can be provided. Specifically, the lithium recovery rate may be 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more, and advantageously, the lithium contained in the clay can be recovered intact without loss.

[0066] In addition, when lithium is recovered by the method according to the present disclosure, the leaching rate of impurities represented by Formula 1 below may be less than 5%, less than 4%, less than 3%, less than 2%, or less than 1%, and advantageously, no impurities may be leached.

[0067] [Equation 1]

[0068] Impurity leaching rate (%) = (w s / w c ) X 100

[0069] In the above Equation 1, w s represents the weight of impurities contained in the lithium-containing solution, and w c represents the weight of impurities contained in the clay.

[0070] In other words, by sequentially performing a series of processes including mixing lithium-containing clay with calcium sulfate, heat treating, leaching with water, and solid-liquid separation, calcium and magnesium contained in the lithium-containing clay are converted into insoluble compounds and removed, thereby enabling the production of high-purity lithium. Calcium and magnesium, which not only account for a larger content than lithium in the clay but also act as impurities that reduce lithium recovery efficiency and purity during the lithium recovery process, can be effectively removed.

[0071] The present invention will be explained in more detail below through examples.

[0072] (Example 1)

[0073] 100g of clay with an average particle size of 1 µm to 2 mm and 10g of calcium sulfate (CaSO4, Sigma Aldrich) were mixed and heat-treated at 1050°C for 1 hour. The heat-treated calcined material was placed into a mortar mill (Retsch, RM 200) and ground for 3 minutes. Subsequently, water was added to the ground calcined material to achieve a pulp density of 30%, and water leaching was performed at 70°C for 1 hour while stirring. The solid-liquid separation of the water leaching product into a lithium-containing solution and residue was performed by vacuum filtration, and the lithium-containing solution was recovered.

[0074] (Example 2)

[0075] The procedure was carried out in the same manner as in Example 1, but the solid-liquid separated residue was fed into a countercurrent washing (CCW) device and washed with water to recover the concentrated lithium-containing solution.

[0076] Specifically, the backflow cleaning device consists of eight cleaning units connected in series, and residue is supplied to the first cleaning unit so that the residue sequentially passes through the first to eighth cleaning units, while water is simultaneously supplied to the eighth cleaning unit to flow water in the opposite direction to the residue to perform backflow cleaning. After the water and residue pass through all cleaning units once, the residual lithium-containing solution recovered from the first cleaning unit is mixed with the lithium-containing solution recovered during solid-liquid separation to recover a concentrated lithium-containing solution.

[0077] (Comparative Example 1)

[0078] Clay was fed into a wet cyclone to perform a beneficiation process, and the concentrate from which gangue had been removed was recovered. 100 g of concentrate and 76 g of sulfuric acid (H2SO4) were added to water to achieve a pulp density of 25%, and acid leaching was performed at room temperature (25℃) for 1 hour. The acid leaching product was separated into a lithium-containing solution and a residue by vacuum filtration, and lithium was recovered.

[0079] (Comparative Example 2)

[0080] The procedure was carried out in the same manner as Example 1, except that magnesium sulfate (MgSO4) was added instead of calcium sulfate.

[0081] (Comparative Example 3)

[0082] The procedure was performed in the same manner as Example 1, except that calcium carbonate (CaCO3) was added instead of calcium sulfate.

[0083] (Comparative Example 4)

[0084] The procedure was carried out in the same manner as Example 1, except that sodium sulfate (Na2SO4) was added instead of calcium sulfate.

[0085] (Evaluation Example 1) Evaluation of X-ray diffraction analysis spectrum

[0086] X-ray diffraction (XRD) analysis of clay, calcined products, and water leaching products was performed using an X-ray diffraction analyzer (Rigaku, MiniFlex 600) and is shown in Figures 2 to 4 below.

[0087] Figures 2 to 4 are XRD spectra for the clay, calcined product, and water leaching product of Example 1, respectively. CaCO3, SiO2, BH2NaO7Si2, and CCa in the clay. 0.5 Mg 0.5 The detection of a peak originating from O3 indicates the presence of large amounts of impurities, such as Si, Ca, and Mg. In the case of calcined products and water leaching products obtained by mixing clay containing large amounts of impurities with calcium sulfate and heat-treating them, peaks corresponding to Ca2MgSi2O7 and CaMgSi2O6 were detected. This confirmed that during the heat treatment process, Mg, Si, and Ca reacted with calcium sulfate to form insoluble salts such as Ca2MgSi2O7 and CaMgSi2O6. These insoluble salts can be easily removed by solid-liquid separation of the water leaching products.

[0088] (Evaluation Example 2) Evaluation of the composition of a lithium-containing solution

[0089] Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) analysis was performed to analyze the composition of the clay and lithium-containing solution. The inductively coupled plasma optical emission spectrometry analysis was performed using Perkin Elmer's AUIO 550 max.

[0090] Specifically, the composition of clay and the lithium-containing solution recovered from the clay was calculated and shown in Table 1 below, and the leaching rate (recovery rate) of each component was calculated according to Formula 1 below and shown in Table 2 below.

[0091] [Equation 1]

[0092] Leaching rate (%) = (w s / w c ) X 100

[0093] (In Equation 1 above, w s represents the mass of any one component contained in the lithium-containing solution, and w c ) refers to the mass of any one component contained in the clay)

[0094] Classification NaCaMgFeCrZn Clay (mg / kg) 8,113 171,243 69,465 5,171 88 955 Example 1 (mg / kg) 2,240 551 N.D.NDNDND Example 2 (mg / kg) 22,255 30 N.D.NDNDND Classification KMnAlLiTiB Clay (mg / kg) 11,153 644 5982,355 5816 71 Example 1 (mg / kg) 1,842 NDND9 38 N.D.35 Example 2 (mg / kg) 28,266 NDND8,973 ND49

[0095] Classification Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Example 1 Example 2 Leaching Rate (%) Na 8 1.4 6 1.1 6.1 8 8.5 5 6.7 5 9.1 Ca 4.8 4.0 1.5 2.3 1.0 1.0 Mg 9 2.6 00000 Fe 5 2.5 00000 Cr 0 000000 Z n 0 000000 K 13.8 5 7.2 18.7 7 8.6 6 7.8 7 2.1 Mn 8 8.8 00000 Al 7 3.1 00000 Li 9 3.9 45.7 10.3 6 9.1 9 6.9 100 Ti 2 3.8 00000 B 6 9.9 16.1 1.0 3 3.3 9 9.0 9.3

[0096] Referring to Tables 1 and 2, it can be seen that the clay contains a small amount of lithium at 2,355 mg / kg, and contains magnesium and calcium at 69,465 mg / kg and 171,243 mg / kg, respectively, indicating that it contains predominantly impurities. When lithium is recovered by treating clay with this composition as in Example 1, Mg and Ca are converted into insoluble salts, allowing for the selective leaching of lithium. Consequently, the solid-liquid separation efficiency is improved, resulting in a high lithium recovery rate of 96.9%. Furthermore, the Ca concentration in the lithium-containing solution decreased to 551 mg / kg, and Mg was not detected, confirming that impurities were effectively removed and high-purity lithium was obtained from the clay using a small amount of calcium sulfate.

[0097] In the case of Example 2, by introducing the residue into a backwasher for washing, the residual lithium-containing solution remaining in the residue without solid-liquid separation was additionally recovered, thereby enabling the recovery of a concentrated lithium-containing solution with a lithium recovery rate of 100%. Consequently, the lithium concentration was significantly improved to 8,973 mg / kg compared to Example 1, and the Ca concentration was significantly reduced to 30 mg / kg compared to Example 1. Thus, it was confirmed that the impurity removal effect and the lithium concentration effect were excellently improved using a simple method.

[0098] When recovering lithium through acid leaching as in Comparative Example 1, a pretreatment process of refining clay to produce a concentrate is necessarily involved. Despite using a concentrate with improved lithium content through pretreatment, Comparative Example 1 showed a lithium recovery rate of only 93.9%, confirming that the lithium recovery performance was low. Furthermore, Comparative Example 1 showed leaching rates of Ca and Mg of 4.8% and 92.6%, respectively, indicating that lithium was not selectively leached during the leaching process, leaving Ca and Mg in the lithium-containing solution, and thus a low-purity lithium-containing solution was recovered.

[0099] Comparative Example 2, which used magnesium sulfate instead of calcium sulfate; Comparative Example 3, which used calcium carbonate instead of calcium sulfate; and Comparative Example 4, which used sodium sulfate instead of calcium sulfate, all showed significantly lower lithium recovery rates compared to Example 1. Comparative Examples 2 to 4 could not selectively leach lithium because the reactivity of converting into a water-soluble compound containing lithium and an insoluble compound containing impurities during the preparation of the calcined product was lower than that of Example 1.

[0100] Therefore, since recovering lithium from clay using compounds other than calcium sulfate results in a significantly low lithium recovery rate, it was confirmed that a high lithium recovery rate and high-purity lithium can be obtained only when calcium sulfate is mixed with clay, heat-treated, and then leached with water.

[0101] As described above, the present invention has been explained by specific details, limited embodiments, and drawings; however, this is provided merely to aid in a more comprehensive understanding of the invention and is not limited to the above embodiments. Those skilled in the art can make various modifications and variations from this description.

[0102] Accordingly, the scope of the present invention is not limited to the described embodiments, and all things equivalent to or having equivalent variations to the claims set forth below, as well as the claims set forth below, shall be considered to fall within the scope of the concept of the present invention.

Claims

1. (S1) A step of preparing a calcined product by heat-treating a mixture of lithium-containing clay and calcium sulfate (CaSO4); (S2) A step of preparing a water-leached product by water-leaching the above-mentioned calcined product; and (S3) A step of separating the above-mentioned water-leaching product into a lithium-containing solution and a residue; a method for recovering lithium.

2. In Paragraph 1, A method for recovering lithium, wherein the above mixture contains 1 to 50 parts by weight of calcium sulfate (CaSO4) based on 100 parts by weight of lithium-containing clay.

3. In Paragraph 1, A lithium recovery method comprising, after the above step (S3), a step (S4) of recovering residual lithium contained in the residue.

4. In Paragraph 3, A lithium recovery method in which the above (S4) step is performed two or more times.

5. In Paragraph 3, A lithium recovery method in which the above (S4) step is performed by a countercurrent washing (CCW) method.

6. In Paragraph 3, A lithium recovery method further comprising, after the above step (S4), (S5) mixing the residual lithium with the lithium-containing solution to recover a concentrated lithium-containing solution.

7. In Paragraph 1, A method for recovering lithium, wherein the above lithium-containing clay contains less than 5000 mg / kg of lithium.

8. In Paragraph 1, A lithium recovery method in which lithium is selectively leached in the above (S2) step.

9. In Paragraph 1, A lithium recovery method in which the calcination of the above (S1) step is performed under temperature conditions of 800 to 1200 ℃.

10. In Paragraph 1, A lithium recovery method further comprising the step of crushing the calcined material after the above step (S1) and before the above step (S2).

11. In Paragraph 1, A lithium recovery method in which the leaching rate of impurities represented by the following Formula 1 is less than 5%. [Equation 1] Leaching rate (%) = (w s / w c ) X 100 (In Equation 1 above, w s represents the weight of impurities contained in the lithium-containing solution, and w c ) refers to the weight of impurities contained in the clay.

12. In Paragraph 1, A lithium recovery method in which the above (S2) step is performed under temperature conditions of 40 to 100 ℃.

13. In Paragraph 1, A lithium recovery method having a lithium recovery rate of 98% or higher.

14. In Paragraph 1, A lithium recovery method in which, in step (S1) above, a water-soluble compound containing lithium and an insoluble compound containing impurities are produced.

15. In Paragraph 14, A method for recovering lithium, wherein the above-mentioned insoluble compound comprises calcium magnesium silicate.

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