Lithium adsorbent

Abstract

The present invention relates to a lithium adsorbent, which is an aluminum hydroxide-based compound and has a grain size of 15 nm or more as determined by the Scherer equation.

Description

lithium adsorbent

[0001] It's about lithium adsorbents.

[0002] There are several methods for recovering lithium from brine, including evaporation and chemical methods, but most involve removing impurities from brine mixed with impurities in advance to obtain a high-concentration lithium solution to obtain useful lithium compounds.

[0003] Recently, there has been active research on recovering lithium using direct lithium extraction technology (DLE technology) from geothermal brine or oil well brine.

[0004] This is a method that utilizes a lithium adsorbent, which is a representative direct lithium extraction technology.

[0005] Lithium adsorbents can selectively recover lithium from brine mixed with impurities, making them advantageous for lithium recovery compared to time-consuming evaporation methods or chemical methods that consume significant amounts of raw materials and generate byproducts. However, data on long-term, repeated operation is still lacking, necessitating further research for commercialization.

[0006] We aim to provide a long-life lithium adsorbent for commercialization.

[0007] In one embodiment of the present invention, a lithium adsorbent is provided, which is an aluminum hydroxide-based compound and has a crystal grain size of 15 nm or more obtained by the Scherer equation.

[0008] The above crystal grain size may be in the range of 15 to 50 nm.

[0009] The above lithium adsorbent can maintain a crystal grain size of 15 nm or more after 1,000 adsorption and desorption cycles.

[0010] The above lithium adsorbent can maintain a crystal grain size of at least 60% of the initial crystal grain size after 1,000 adsorption and desorption cycles.

[0011] The above lithium adsorbent may have a strength change of 15% or less after 1,000 adsorption and desorption cycles.

[0012] The crystal grain size obtained by the above Scherer equation can be obtained by the following mathematical equation 1.

[0013] [Mathematical Formula 1]

[0014]

[0015] τ: grain size (average size, nm)

[0016] K: shape factor (dimensionless, determined by the actual shape of the crystal)

[0017] λ: X-ray wavelength (nm)

[0018]

[0019] β: Half width (FWHM) of the maximum intensity peak (unit: radians)

[0020] θ: X-ray incidence angle (˚)

[0021] The above aluminum hydroxide compound can be represented by the following chemical formula 1.

[0022]

[0023] [Chemical Formula 1]

[0024] LiA·xAl(OH)3·nH2O

[0025] (In the above chemical formula 1, A is at least one of the halogen elements, and 0 <x<5, 및 0<n<10이다.)

[0026] It can provide a long-life adsorbent for commercialization, thereby reducing operating costs of process equipment.

[0027] Figure 1 shows XRD data of an adsorbent manufactured according to an example and an adsorbent that has been adsorbed and desorbed about 1,000 times or more.

[0028] Figures 2 and 3 are XRD data of existing adsorbents.

[0029] Figure 4 shows SEM images of the initial adsorbent and the adsorbent after approximately 1,000 adsorption and desorption cycles.

[0030] Figure 5 shows the results of adsorption performance evaluation according to adsorption and desorption recovery.

[0031] Figure 6 shows the results of strength performance evaluation according to adsorption and desorption recovery.

[0032] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention. The present invention is defined solely by the scope of the claims set forth below.

[0033] LiCl·2Al(OH)3·nH2O, a lithium adsorbent, contains pores into which lithium can enter the Al(OH)3 double layer, and Cl ions or water exist between the layers.

[0034] As adsorption progresses, lithium ions are adsorbed into the pores, and Cl ions accumulate between the layers. As desorption progresses, lithium ions are desorbed together with the Cl ions between the layers, and are recovered as LiCl. Since other impurities are not adsorbed, more efficient lithium recovery is possible.

[0035] A lithium adsorbent according to one embodiment of the present invention may be an aluminum hydroxide-based compound and a lithium adsorbent having a crystal grain size of 15 nm or more obtained by the Scherer equation.

[0036] The above crystal grain size may range from 15 to 50 nm. The initial crystal grain size of the manufactured adsorbent may affect its longevity.

[0037] When adsorption and desorption are repeated, the size of the crystal grains may gradually decrease.

[0038] The above lithium adsorbent can maintain a crystal grain size of 15 nm or 20 nm or more after 1,000 adsorption and desorption cycles. This ensures a certain level of performance even after long-term use of the adsorbent.

[0039] Specifically, the lithium adsorbent can maintain a crystal grain size of at least 60% of the initial crystal grain size after 1,000 adsorption and desorption cycles.

[0040] Additionally, the lithium adsorbent may exhibit a strength change of less than 15% after 1,000 adsorption and desorption cycles. If the strength of the adsorbent changes, the pellet structure deforms, causing problems with process maintenance and affecting adsorption performance.

[0041] The crystal grain size obtained by the above Scherer equation can be obtained by the following mathematical equation 1.

[0042] [Mathematical Formula 1]

[0043]

[0044] τ: grain size (average size, nm)

[0045] K: shape factor (dimensionless, determined by the actual shape of the crystal)

[0046] λ: X-ray wavelength (nm)

[0047]

[0048] β: Half width (FWHM) of the maximum intensity peak (unit: radians)

[0049] θ: X-ray incidence angle (˚)

[0050] The above aluminum hydroxide compound can be represented by the following chemical formula 1.

[0051]

[0052] [Chemical Formula 1]

[0053] LiA·xAl(OH)3·nH2O

[0054] (In the above chemical formula 1, A is at least one of the halogen elements, and 0 <x<5, 및 0<n<10이다.)

[0055]

[0056] LiCl·2Al(OH)3·nH2O, an Al-based layered lithium adsorbent, can be obtained by quantitatively mixing AlCl3·nH2O and LiCl in distilled water and then adding NaOH.

[0057] More specifically, it can be manufactured through the following process.

[0058] A method for producing an aluminum-based lithium adsorbent according to one embodiment includes a step of adding an aqueous sodium hydroxide solution to a mixed solution of aluminum chloride and lithium chloride, and a step of producing a lithium adsorbent through a one-step reaction of the mixed solution and the aqueous sodium hydroxide solution.

[0059] First, prepare a mixed solution of aluminum chloride and lithium chloride.

[0060] The above mixed solution is prepared by dissolving aluminum chloride and lithium chloride in distilled water so that the molar ratio is 1:1 to 4:1, more specifically 2:1 to 3:1.

[0061] When the molar ratio of aluminum chloride and lithium chloride satisfies the above range, the pH range reaches 5 to 10, and the yield of the synthesized adsorbent is the highest at this time.

[0062] This coincides with the lowest solubility condition of aluminum hydroxide, the main compound in the adsorbent. Below this pH range, the adsorbent loses filterability and struggles to function as an adsorbent.

[0063] At this time, the mixed solution may be stirred. The stirring may be performed at a level where the solution can flow.

[0064] More specifically, it can be stirred at a speed of 100 rpm to 1,000 rpm.

[0065] Next, add sodium hydroxide aqueous solution to the above mixed solution.

[0066] Specifically, the addition of the sodium hydroxide aqueous solution can be performed by adding the entire required amount at once or by uniformly adding a predetermined amount over 30 to 90 minutes.

[0067] At this time, when a sodium hydroxide aqueous solution is injected in batches, the synthesis of an adsorbent having a size of several nanometers is possible. Furthermore, when a predetermined amount is uniformly injected over a period of 30 to 90 minutes, the synthesis of an adsorbent having a size of several hundred nanometers is possible.

[0068] Thus, the difference in the method of adding the sodium hydroxide aqueous solution results in a difference in the amount of binder particles added in the molding process described below. That is, for an adsorbent having a size of several nanometers, the binder input content increases compared to an adsorbent having a size of several hundred nanometers.

[0069] The process of injecting a fixed amount of sodium hydroxide aqueous solution at a fixed rate, i.e., the process of uniformly injecting a fixed amount over a period of 30 to 90 minutes, can be performed at, for example, 30 ml / min to 100 ml / min. When the sodium hydroxide aqueous solution is injected into the mixed solution under these conditions, there is an advantage in that the particle size distributed within the adsorbent can be controlled and a homogeneous lithium adsorbent with good crystallinity can be obtained.

[0070] Meanwhile, the above sodium hydroxide aqueous solution is prepared by dissolving sodium hydroxide in water to a concentration of 4 to 8 mol, more specifically, 5 to 8 mol. When the concentration of the sodium hydroxide aqueous solution satisfies the above range, a crystalline powder with good adsorption characteristics can be produced.

[0071] Next, a lithium adsorbent can be manufactured through a one-step reaction of the above mixed solution and an aqueous sodium hydroxide solution.

[0072] The above reaction can be carried out at a temperature ranging from 50°C to 150°C and a speed of 200 rpm to 1000 rpm. More specifically, it is preferable to carry out the reaction at a temperature ranging from 60°C to 100°C and a speed of 300 rpm to 700 rpm for 1 to 3 hours.

[0073] When these reaction conditions are satisfied, aluminum hydroxide and lithium chloride, which are produced by the addition of sodium hydroxide, react to form a slurry, and lithium ions combine with aluminum hydroxide to synthesize the adsorbent.

[0074] The above 1-step process includes a process of washing the lithium adsorbent slurry.

[0075] The process of washing the lithium adsorbent slurry can be performed using, for example, washing water 3 to 10 times the weight of the lithium adsorbent slurry.

[0076] For washing water, at least one of distilled water or regular tap water can be used.

[0077] In this embodiment, the above reaction and the process of washing the lithium adsorbent slurry can be performed simultaneously. Therefore, a separate washing process is not required, simplifying the process and thus improving the productivity of the aluminum-based lithium adsorbent.

[0078] The above washing process is, more specifically, washing the cake obtained after separating the lithium adsorbent slurry into solid and liquid through vacuum filtration or the like.

[0079] By conducting a washing process under these conditions, the sodium chloride (NaCl) contained within the cake can be washed away. Furthermore, this washing process can activate the adsorption sites of the lithium adsorbent.

[0080] Next, the washed cake is dried in a dryer for at least 8 hours, or more specifically, 8 to 48 hours. If the cake has a moisture content of around 60%, drying is possible in just 8 hours. However, if the moisture content is higher than 60%, drying time of 48 hours or more is required.

[0081] The drying process is preferably performed at a temperature ranging from 40°C to 60°C, more specifically, from 45°C to 50°C. When the temperature of the drying process satisfies the above range, the composition of the adsorbent remains unchanged, thereby producing a lithium adsorbent with excellent adsorption performance. This is because, when the temperature of the drying process exceeds 60°C, the properties of aluminum hydroxide change, making it impossible to maintain its properties as an adsorbent.

[0082] Meanwhile, the method for manufacturing an aluminum-based adsorbent according to the present embodiment may further include a molding process after the step of manufacturing the lithium adsorbent.

[0083] The forming process may be performed by forming the lithium adsorbent into a cylindrical pellet shape, for example. The cylindrical pellet-type lithium adsorbent may be manufactured, for example, by an extrusion process.

[0084] More specifically, the extrusion process involves filling a cylinder with a fluid raw material dough and extruding it through a mold of a predetermined shape, thereby continuously forming the material. At this time, a binder is added to the lithium adsorbent manufactured by the aforementioned method to form a dough with a predetermined viscosity, which can then be used as the raw material dough.

[0085] Next, the lithium adsorbent formed according to the shape of the mold can be implemented to have a constant cross-sectional shape such as rectangular, circular, or T-shaped.

[0086] Meanwhile, the extruder used for the extrusion may be, for example, a screw type or a piston type.

[0087] The screw type has the advantage of being able to push out high viscosity dough through the power of the screw, and the piston type has less power than the screw type, but is advantageous in extruding complex shapes such as honeycomb shapes.

[0088] The most important factor during extrusion is the condition of the raw material dough. If the viscosity is too low, there is a problem of weak strength of the molded lithium adsorbent, and if the viscosity is too high, there is a problem of reduced productivity.

[0089] Therefore, it is important to prepare the raw material dough with an appropriate viscosity.

[0090] That is, although molding can be performed using a lithium adsorbent manufactured by the method described above, the lithium adsorbent formed in this manner may be broken during the process of repeating continuous adsorption and desorption processes with a lithium-containing solution.

[0091] Accordingly, a lithium adsorbent formed by mixing an organic or inorganic binder into a lithium adsorbent manufactured by a method according to one embodiment can be manufactured to maintain a constant strength and shape.

[0092] As a binder that can be used in the molding process according to the present embodiment, a non-aqueous binder including at least one of polyvinyl chloride, vinyl chloride, polyethylene, and combinations thereof can be used. Alternatively, a solvent and binder used in non-aqueous ceramic molding can be mixed with the aforementioned lithium adsorbent and then extrusion molded.

[0093] Meanwhile, the currently commercialized aluminum-based adsorbent synthesizes a lithium adsorbent by adsorbing lithium chloride, lithium sulfate, lithium nitrate, etc. onto aluminum hydroxide, and then adsorbs lithium into a lithium-containing solution and extracts lithium by desorption using water.

[0094] In particular, the adsorbent combined with lithium chloride is synthesized by first synthesizing aluminum hydroxide, then washing away the reaction byproducts, sodium chloride or ammonium chloride, and then adsorbing lithium chloride thereon to synthesize the final lithium adsorbent.

[0095] Lithium adsorbents synthesized this way have low filterability, making it difficult to repeat the lithium adsorption / desorption process. To address this issue, a method has been proposed in which the adsorbent is molded into a specific shape or size and then brought into contact with a lithium adsorption solution. However, the low lithium adsorption capacity in the absence of solution flow makes it difficult to directly apply it to the lithium adsorption process.

[0096] In addition, to solve these problems, the process can be configured as a fluid solution immersion process, but even in this case, since the final adsorbent is obtained through an activation process that creates a space for lithium to be adsorbed before lithium is adsorbed, multiple processes are required, and there is a problem that the lithium adsorption performance decreases during this process.

[0097] However, in the present embodiment, the synthesis of the lithium adsorbent is carried out in a one-step process, and since the one-step process includes a washing process, activation of the adsorption sites in the lithium adsorbent is possible, so that a separate activation process is not required, thereby drastically simplifying the process. Moreover, the adsorption performance of the lithium adsorbent manufactured in this way is also significantly improved compared to conventional commercialized aluminum-based lithium adsorbents.

[0098]

[0099] Hereinafter, preferred embodiments and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0100]

[0101] Example

[0102] Lithium adsorbent can be manufactured in the form of LiCl·2Al(OH)3·nH2O by adding NaOH to a mixed solution of AlCl3·nH2O and LiCl using a one-step method.

[0103] Specifically, a 50% NaOH solution was injected at a rate of 35 mL / min. When the injection volume increased, the injection rate was approximately 0.8 to 1.5 wt% / min. This represents a 20 to 30 times slower rate than before.

[0104] The manufactured adsorbent was filtered and dried in an oven at 40 to 60°C. The dried adsorbent was then mixed with a binder in powder form to form a paste, and then manufactured into pellets using a molding machine. The manufactured adsorbent molded body was filled into a 100 mL column, and its performance was measured by repeating adsorption and desorption more than 1,000 times.

[0105] The brine used for adsorption and desorption was a simulated brine having the same composition as real brine containing 1 g / L of lithium.

[0106] Figure 5 is a graph showing the calculated adsorption capacity by measuring the lithium concentration of the filtrate during adsorption and desorption. Adsorption capacity is defined as the amount of lithium adsorbed per g of adsorbent weight. The experimental results show that the adsorbent maintains an adsorption capacity of 6 mg / g during repeated tests over 1,000 times, and as shown in Figure 5, the strength also maintains a level that has decreased by approximately 11% after about 300 adsorption and desorption cycles from the initial level even after repeated tests over 1,000 times.

[0107] However, in Fig. 4, it can be seen that the pores of the pellets have increased compared to the initial adsorbent pellets, which indicates that some damage to the adsorbent has occurred after more than 1,000 repetitions.

[0108] Looking at the XRD results in Figure 1, we can see that the peaks have increased in width overall. This means that the crystal grain size of the adsorbent has decreased, and consequently, we can see that the adsorbent surface is damaged during long-term operation.

[0109] The size of the crystal grains can be determined by the Scherer equation, which states that the FWHM (Full Width at Half Maximum) and the crystal grain size are inversely proportional.

[0110] [Mathematical Formula 1]

[0111]

[0112] Here, the meaning of each symbol is as follows.

[0113] τ: average grain size

[0114] K: Shape factor (dimensionless number), approximately 0.9, but varies depending on the actual shape of the crystal.

[0115] λ: X-ray wavelength

[0116] β: Half width (FWHM) of the maximum intensity peak (unit: radians)

[0117] θ: X-ray incidence angle

[0118] According to this equation, the representative peak of this adsorbent is 2θ = 11.5 o Calculating the crystal grain size reveals that the initial crystal grain size is approximately 32 nm, but after more than 1,000 adsorption / desorption cycles, the size decreases by approximately 34% to 21 nm. However, considering that other performance changes are not significant, it can be confirmed that the crystal grain size is maintained at a certain level.

[0119] The strength was measured using a compressive strength tester. The results are shown in Fig. 6.

[0120] The adsorbent pellet was placed on the measuring device and the pressure was gradually increased. The pressure at the moment the pellet broke was reduced, and the pressure value at this time was defined as the compressive strength.

[0121] Assuming that the height of the adsorbent column to be used in the actual process is 2 m, the pressure applied to the adsorbent pellet located at the bottom when full of solution and adsorbent was calculated to be approximately 1.3 MPa, and considering other additional pressure factors, it was estimated that there would be no problem in terms of the compressive strength of the adsorbent if it was 10 MPa or more.

[0122]

[0123] Comparative example

[0124] From the XRD results described in the two foreign patents, the grain size can be calculated through the representative peaks at the same positions for the lithium adsorbent.

[0125] Figure 2 shows the XRD results described in patent WO2015-097204. From this, it can be seen that the crystal grain size is approximately 7.5 nm.

[0126] Figure 3 shows the crystal grain size of a lithium adsorbent of another patent, CN 101829538. From this, it can be seen that the crystal grain size is approximately 14 nm.

[0127] As the crystal grain size decreases with repeated adsorption and desorption over a long period of time, if the initial crystal grain size is small, its lifespan may be short.

[0128]

[0129] The present invention is not limited to the above-described embodiments, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. It is an aluminum hydroxide compound, A lithium adsorbent having a crystal grain size of 15 nm or more obtained by the Scherer equation.

2. In paragraph 1, A lithium adsorbent having a crystal grain size in the range of 15 to 50 nm.

3. In paragraph 1, The above lithium adsorbent is a lithium adsorbent, wherein the crystal grain size is maintained at 15 nm or more after 1,000 adsorption and desorption cycles.

4. In paragraph 1, The above lithium adsorbent is a lithium adsorbent, wherein the crystal grain size after 1,000 adsorption and desorption cycles is maintained at 60% or more of the initial crystal grain size.

5. In paragraph 1, The above lithium adsorbent is a lithium adsorbent, wherein the strength change after 1,000 adsorption and desorption cycles is 15% or less.

6. In paragraph 1, A lithium adsorbent having a crystal grain size obtained by the Scherer equation above, which is obtained by the following mathematical equation 1. [Mathematical formula 1] τ: Grain size (average size, nm) K: Shape factor (dimensionless, determined by the actual shape of the crystal) λ: X-ray wavelength (nm) β: Half width (FWHM) of the maximum intensity peak (unit: radians) θ: X-ray incidence angle (˚) 7. In paragraph 1, The above aluminum hydroxide compound is a lithium adsorbent represented by the following chemical formula 1. [Chemical Formula 1] LiA·xAl(OH)3·nH2O (In the chemical formula 1 above, A is at least one of the halogen elements, and 0 <x<5, 및 0<n<10이다.)

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