JP7581064B2 - Lithium ion recovery system and lithium ion recovery method - Google Patents

Description

The present invention relates to a lithium ion recovery system and a lithium ion recovery method.

Producing lithium from the brine of a salt lake is one of the most common methods for mining natural lithium. It is also being considered to recover lithium from waste materials such as used lithium-ion batteries, and to produce lithium from seawater. When the raw material is the brine of a salt lake, it is concentrated by solar evaporation, and then impurities such as magnesium ions are removed from the brine using a precipitating reagent. Lithium is recovered in the form of lithium carbonate by adding a precipitating reagent such as sodium carbonate to the brine.

Alternatives to concentrating the brine by solar evaporation have also been proposed. US Pat. No. 5,399,433 proposes recovering lithium from aqueous solutions by a method called solvent extraction. US Pat. No. 5,499,433 proposes recovering lithium from aqueous solutions by a method called adsorption.

Patent No. 4581553 JP 2009-161794 A

The method of producing lithium from salt lake brine has several drawbacks. First, the process of concentrating the brine by solar evaporation takes a very long time, about two years. Large-scale salt fields are required, resulting in huge initial costs. If the brine contains a large amount of SO ₄ ^2- , it is difficult to highly concentrate the brine containing a large amount of SO ₄ 2-, because lithium sulfate precipitates during the concentration, reducing the lithium recovery rate. Large amounts of precipitating reagents are required to remove divalent ions. Divalent ions such as SO ₄ ^{2- and} Mg ²⁺ are mixed into the product as impurities, so additional purification is required.

The solvent extraction method described in Patent Document 1 requires heating and mixing operations to increase the contact area between the oil phase and the liquid phase and improve the exchange efficiency. This tends to result in a large facility footprint. In addition, the extraction process and back-extraction process are performed in two separate steps, which is time-inefficient. In other words, the solvent extraction method is not suitable for continuous lithium production. Furthermore, many extraction solvents have the property of corroding metals. For this reason, it is necessary to use expensive piping, such as corrosion-resistant lined piping or fluororesin piping, for the extraction solvent.

The adsorption method described in Patent Document 2 also requires two steps, an adsorption step and a desorption step, and is therefore unsuitable for continuous lithium production. When lithium-containing saltwater is brought into contact with an adsorbent to adsorb lithium ions onto the adsorbent, a pressure difference is likely to occur inside the column packed with the adsorbent, making it difficult for the saltwater to come into uniform contact with the adsorbent. Another disadvantage is that high pressure is required to introduce the saltwater into the column.

The purpose of the present invention is to provide a new technology that can be used to recover lithium.

The present invention relates to
A nanofiltration membrane module for treating a solution containing lithium ions;
a lithium ion permeable membrane module disposed downstream of the nanofiltration membrane module so that a permeate of the nanofiltration membrane module is supplied thereto, the lithium ion permeable membrane module having a lithium ion permeable membrane that selectively allows the lithium ions to pass therethrough;
The present invention provides a lithium ion recovery system comprising:

In another aspect, the present invention provides a method for producing a composition comprising:
a lithium ion permeable membrane module having a lithium ion permeable membrane that selectively permeates lithium ions contained in the first solution;
a reverse osmosis membrane module disposed downstream of the lithium ion permeable membrane module so as to supply a second solution containing the lithium ions that have permeated the lithium ion permeable membrane module;
The present invention provides a lithium ion recovery system comprising:

In yet another aspect, the present invention provides a method for producing a composition comprising:
treating a solution containing lithium ions through a nanofiltration membrane;
treating the nanofiltration membrane permeate with a lithium ion permeable membrane that selectively permeates the lithium ions;
The present invention provides a method for recovering lithium ions, comprising:

In yet another aspect, the present invention provides a method for producing a composition comprising:
treating the first solution containing lithium ions with a lithium ion permeable membrane that selectively allows lithium ions to pass therethrough;
treating the second solution containing the lithium ions that have permeated the lithium ion permeable membrane with a reverse osmosis membrane;
The present invention provides a method for recovering lithium ions, comprising:

The present invention can be used to recover lithium.

FIG. 1 is a configuration diagram of a lithium ion recovery system according to a first embodiment of the present invention. FIG. 2 is a diagram showing the function of the lithium ion permeable membrane. FIG. 3 is a diagram showing a manufacturing process of a lithium ion permeable membrane. FIG. 4 is a schematic cross-sectional view of a lithium ion permeable membrane module using a lithium ion permeable membrane. FIG. 5 is a configuration diagram of a lithium ion recovery system according to a second embodiment of the present invention. FIG. 6 is a configuration diagram of a lithium ion recovery system according to a third embodiment of the present invention.

Embodiments of the present invention will be described below with reference to the drawings. The present invention is not limited to the following embodiments.

First Embodiment
FIG. 1 is a configuration diagram of a lithium ion recovery system according to a first embodiment of the present invention. The lithium ion recovery system 100 includes a nanofiltration membrane module 30 and a lithium ion permeable membrane module 40. The lithium ion permeable membrane module 40 is a module having a lithium ion permeable membrane that selectively allows lithium ions to pass through. The lithium ion permeable membrane module 40 is disposed downstream of the nanofiltration membrane module 30 so that the permeate of the nanofiltration membrane module 30 is supplied to the lithium ion permeable membrane module 40. In this specification, the "nanofiltration membrane" is referred to as "NF membrane".

The NF membrane module 30 is a module using an NF membrane, which allows monovalent ions such as Li ⁺ , Na ⁺ , and K ⁺ to pass through, and blocks divalent ions such as Mg ²⁺ and SO ₄ ^2- . In the NF membrane module 30, monovalent ions and divalent ions are separated. The lithium ion permeable membrane module 40 allows Li ⁺ to pass through, and blocks monovalent ions other than Li ⁺ . In other words, the lithium ion recovery system 100 is configured to separate and recover lithium ions from a raw solution containing lithium ions and other metal ions. The lithium ion permeable membrane 10 used in the lithium ion permeable membrane module 40 may have a property that the permeation rate of lithium ions decreases due to the presence of Mg ²⁺ . By removing divalent ions in advance using the NF membrane module 30, the permeation rate of lithium ions in the lithium ion permeable membrane module 40 can be improved. As a result, the decrease in the recovery efficiency of lithium in the lithium ion permeable membrane module 40 is suppressed, and lithium can be recovered efficiently.

To efficiently remove Mg ²⁺ ions by precipitation with CaO, the raw solution must be concentrated.

The NF membrane module 30 and the lithium ion permeable membrane module 40 are connected in this order by the flow path 2b. The permeate outlet of the NF membrane module 30 and the first inlet (supply side inlet) of the lithium ion permeable membrane module 40 are connected by the flow path 2b. The raw water inlet of the NF membrane module 30 is connected to the flow path 2a. The concentrated water outlet of the NF membrane module 30 is connected to the flow path 2d. The first outlet (supply side outlet) of the lithium ion permeable membrane module 40 is connected to the flow path 2e. The second inlet (permeation side inlet) of the lithium ion permeable membrane module 40 is connected to the flow path 2f. The second outlet (permeation side outlet) of the lithium ion permeable membrane module 40 is connected to the flow path 2c. Each of the flow paths 2a, 2b, 2c, 2d, 2e, and 2f is composed of one or more pipes. If necessary, equipment such as pumps, valves, and sensors may be arranged in each of the flow paths 2a, 2b, 2c, 2d, 2e, and 2f. Flow paths 2a, 2b, 2c, 2d, 2e, and 2f may have buffer tanks.

The type of raw solution containing lithium ions and other metal ions is not particularly limited. The raw solution is typically an aqueous solution. Examples of raw solutions include seawater, lake water, brackish water, and industrial wastewater. Lake water is groundwater from salt lakes (such as Salar de Uyuni and Salar de Atacama) that contain high concentrations of lithium. Industrial wastewater is typically a solution produced in the process of recovering lithium from industrial waste such as used lithium-ion batteries.

The raw solution may be previously treated to remove solutes with large particle sizes, such as solids, bacteria, and colloids. In other words, a pretreatment device may be placed upstream of the NF membrane module 30. Examples of pretreatment devices include a settling device, a sand filter, a diatomaceous earth filter, a mesh filter, a MF (microfiltration) membrane module, and a UF (ultrafiltration) membrane module. One or a combination of two or more selected from these may be used as the pretreatment device.

The lithium ion permeable membrane 10 of the lithium ion permeable membrane module 40 does not have the ability to permeate water. Therefore, the liquid used to recover the lithium ions is supplied to the lithium ion permeable membrane module 40 through the flow path 2f. The liquid used to recover the lithium ions is, in detail, an acidic aqueous solution. Hydrochloric acid or carbonated water is preferably used as the acidic aqueous solution.

(NF membrane module)
The NF membrane module 30 treats (filters) the raw solution containing lithium ions. The NF membrane module 30 allows some of the monovalent ions to pass through while blocking divalent ions. The concentrated water from the NF membrane module 30 contains divalent ions such as Mg ²⁺ and SO ₄ ²⁻ . The permeated water from the NF membrane module 30 contains monovalent ions such as Li ⁺ , Na ⁺ , and K ⁺ .

In this specification, "NF membrane" refers to a separation membrane that has a sodium chloride rejection rate of 5% or more and less than 93% when an aqueous sodium chloride solution with a concentration of 2000 mg/liter is filtered under conditions of an operating pressure of 0.7 MPa, pH 6.5-8, recovery rate of 15%, and 25°C. "RO membrane" refers to a separation membrane that has a sodium chloride rejection rate of 93% or more when an aqueous sodium chloride solution with a concentration of 2000 mg/liter is filtered under conditions of an operating pressure of 1.5 MPa, pH 6.5-8, recovery rate of 15%, and 25°C.

The rejection rate of monovalent ions can be measured by the following method in accordance with JIS K 3805 (1990). An aqueous NaCl solution is permeated through a separation membrane of a predetermined size at an operating pressure of 0.7 MPa or 1.5 MPa. After completion of a 30-minute preparation stage, the conductivity of the permeated liquid and the feed liquid is measured using a conductivity measuring device, and the NaCl rejection rate as the rejection rate of monovalent ions can be calculated based on the results and the calibration curve (concentration-conductivity) according to the following formula. Instead of measuring the conductivity, the concentration may be measured by ion chromatography.
NaCl rejection rate (%) = (1 - (NaCl concentration of permeate / NaCl concentration of feed)) x 100

In order to confirm that monovalent ions and divalent ions can be separated using the NF membrane module 30, the following experiment was carried out. A commercially available NF membrane module was used as the NF membrane module 30. As simulated water containing lithium ions, an aqueous solution containing 30 wt% NaCl, Mg ²⁺ , SO ₄ ^2- and Li ⁺ at concentrations of 800 mg/L, 16000 mg/L and 600 mg/L, respectively, was prepared. The simulated water was filtered through the NF membrane module, and the concentration of each ion contained in the permeated water was measured by an inductively coupled plasma optical emission spectrometer for cations and by ion chromatography for anions. The measurement results were used to calculate the rejection rate according to the following formula. The results are shown in Table 1.
Rejection rate (%) = (1 - (ion concentration of permeate / ion concentration of feed solution)) x 100

As shown in Table 1, by filtering the simulated water with the NF membrane module, it was possible to separate the divalent ions magnesium ions and sulfate ions from the monovalent ions lithium ions. In other words, with the exception of Na ions and Cl ions, the concentrated water mainly contained magnesium ions and sulfate ions, and the permeate mainly contained lithium ions.

The structure of the NF membrane module 30 is not particularly limited. Examples of the structure of the NF membrane module 30 include a spiral type, a hollow fiber type, a tubular type, and a frame and plate type. The NF membrane module 30 may have only one membrane element, or may have multiple membrane elements.

(Lithium ion permeable membrane module)
The lithium ion permeable membrane module 40 has a lithium ion permeable membrane 10, a first flow path 401, and a second flow path 402. The lithium ion permeable membrane 10 includes a polymer substrate and a lithium extractant. The lithium extractant is held in the polymer substrate. The lithium extractant selectively captures and releases lithium ions. The lithium extractant acts to selectively allow the lithium ions to permeate the lithium ion permeable membrane 10. This makes it possible to selectively recover lithium ions from solutions containing various metal ions, such as seawater, lake water, and industrial wastewater.

The polymer substrate constitutes the matrix of the lithium ion permeable membrane 10 and plays a role in ensuring the strength of the lithium ion permeable membrane 10. The polymer substrate is not particularly limited, and examples thereof include cellulose acetate, cellulose triacetate, polyvinyl chloride, and polyvinylidene fluoride. As the polymer substrate, only one selected from these materials may be used, or a combination of two or more may be used. Among them, at least one selected from the group consisting of cellulose acetate and cellulose triacetate is preferably used. These are advantageous in ensuring the strength of the lithium ion permeable membrane 10, and are insoluble, so that the lithium ion permeable membrane 10 can be used for various purposes.

The content ratio of the polymer base material in the lithium ion permeable membrane 10 is, for example, in the range of 30 wt % to 90 wt %. By appropriately adjusting the content ratio of the polymer base material, the above-mentioned effects can be further enhanced.

The lithium extractant is a material that selectively captures and releases lithium ions. In particular, the lithium extractant can be a material that forms a complex with lithium ions. The complex is, for example, a chelate complex. As a material having such properties, the lithium extractant includes at least one selected from the group consisting of phosphorus compounds having a P=O bond and β-diketones. These materials have excellent properties of selectively capturing lithium ions, and are therefore suitable as lithium extractants.

(Phosphorus compounds)
The phosphorus compound has a P=O bond. The phosphorus compound may be an organic phosphorus compound. Examples of the phosphorus compound include phosphine oxide, phosphonic acid (phosphorus oxo acid), and phosphate (phosphate ester). The phosphorus compound is represented by, for example, the following formula (1).

In formula (1), X, Y and Z are each independently a single bond, an ether group, an oxygen atom or a group represented by N-R ^4. R ¹ , R ² , R ³ and R ⁴ are each independently a hydrogen atom, a C1-C20 hydrocarbon group or a C1-C20 aromatic substituent. At least a part of the hydrogen atoms in the hydrocarbon group may be substituted with fluorine atoms. The aromatic substituent may have a heteroatom. When the phosphorus compound is an organic phosphorus compound, at least one of R ¹ , R ² , R ³ , X, Y and Z has a carbon atom. As the phosphorus compound, only one selected from the above-mentioned compounds may be used, or a combination of two or more may be used.

(β-diketone compound)
The β-diketone compound means an organic compound having a β-diketone. A β-diketone is a diketone having a structure in which one carbon atom exists between two ketone groups. Specifically, the β-diketone compound is represented by the following formula (2).

In formula (2), ^R5 and ^R6 are each independently a hydrogen atom, a C1-C20 hydrocarbon group, or a C1-C20 aromatic substituent. At least a part of the hydrogen atoms in the hydrocarbon group may be substituted with fluorine atoms. The aromatic substituent may have a heteroatom. As the β-diketone compound, only one selected from the above-mentioned compounds may be used, or two or more may be used in combination.

The content ratio of the lithium extractant in the lithium ion permeable membrane 10 is, for example, in the range of 10 wt % to 70 wt %. When both a phosphorus compound and a β-diketone compound are used as the lithium extractant, the content ratio of the phosphorus compound in the lithium ion permeable membrane 10 is, for example, in the range of 5 wt % to 65 wt %. The content ratio of the β-diketone compound in the lithium ion permeable membrane 10 is, for example, in the range of 5 wt % to 65 wt %. By appropriately adjusting the content ratios of these materials, it is possible to increase the lithium recovery efficiency while also ensuring the durability of the lithium ion permeable membrane 10.

As another material, the lithium ion permeable membrane 10 may contain a plasticizer. When the raw material solution for the lithium ion permeable membrane 10 contains a plasticizer, it may be possible to produce a porous lithium ion permeable membrane 10. The lithium ion permeable membrane 10 may contain no other materials and may essentially consist of the polymer base material and the lithium extractant. "Consists essentially of..." means that, with the exception of unavoidable impurities such as residual solvents, no materials other than the polymer base material and the lithium extractant are actively used.

The thickness of the lithium ion permeable membrane 10 is not particularly limited, and is, for example, in the range of 1 μm to 100 μm. As the thickness increases, the durability of the lithium ion permeable membrane 10 increases. As the thickness decreases, the lithium ion recovery speed increases. There is a trade-off between durability and recovery speed. By appropriately adjusting the thickness of the lithium ion permeable membrane 10, it is possible to achieve a balance between the lithium ion recovery speed and the durability of the lithium ion permeable membrane 10.

2 is a diagram showing the function of the lithium ion permeable membrane 10. The lithium ion permeable membrane 10 has a first main surface 10p and a second main surface 10q. The lithium ion permeable membrane 10 divides the container 20 into two parts. One part of the container 20 contains a first solution 22 containing lithium ions. The other part of the container 20 contains a second solution 24. The first main surface 10p of the lithium ion permeable membrane 10 is in contact with the first solution 22. Each of the one part and the other part of the container 20 is provided with an agitator 23 so that the first solution 22 and the second solution 24 can be agitated. The second main surface 10q of the lithium ion permeable membrane 10 is in contact with the second solution 24. The "main surface" means the surface having the largest area.

Lithium ions are captured (i.e., extracted) by the lithium extractant on the first main surface 10p of the lithium ion permeable membrane 10. Lithium ions are released (i.e., back-extracted) from the lithium extractant on the second main surface 10q of the lithium ion permeable membrane 10. By utilizing this property, a flow process in which extraction and back-extraction are performed continuously can be realized.

The first solution 22 is a solution containing lithium ions and is a solution that supplies lithium ions. In particular, the first solution 22 is an alkaline aqueous solution containing lithium ions. The pH of the first solution 22 is adjusted to a range of pH=9.0 to 12.5, for example. In order to adjust the pH to an alkaline range, a pH adjuster that dissolves in water to generate hydroxide ions, such as NaOH, KOH, or _NH3 , may be added to the first solution 22.

The second solution 24 is a solution that receives lithium ions. The second solution 24 is an acidic aqueous solution. The pH of the second solution 24 is adjusted to, for example, a range of pH=1.0 to 4.0. In order to adjust the pH to an acidic state, a pH adjuster that dissolves in water to generate protons, such as HCl, H ₂ SO ₄ , HNO ₃ , or CO _2, may be added. When the final target is lithium carbonate, CO ₂ is suitable as a pH adjuster. When the pH of the second solution 24 needs to be adjusted, a gaseous pH adjuster may be bubbled into the second solution 24, or the pH adjuster may be directly mixed into the second solution 24.

As shown in FIG. 2, when the first solution 22 is brought into contact with the first main surface 10p and the second solution 24 is brought into contact with the second main surface 10q, the lithium ions react with the lithium extractant at the interface between the first main surface 10p and the first solution 22 to form a lithium complex 12 (chelate complex). When forming a complex with the lithium ions, the lithium extractant releases protons to the first solution 22. This reaction is represented by the following formula (3). In formula (3), trioctylphosphine oxide (TOPO), which is a phosphorus compound, and thenoyltrifluoroacetone (TTA), which is a β-diketone compound, are assumed as lithium extractants. Thenoyltrifluoroacetone is known as a chelating agent. "aq" indicates that the substance exists in an aqueous solution. "mem" indicates that the substance exists in a lithium ion-permeable membrane.

The reaction rate of the complexation represented by formula (3) is the factor that governs the selectivity of the lithium ion permeable membrane 10. The lithium extractant selectively forms a complex with the lithium ion. Sodium ions and potassium ions cannot form a complex with the lithium extractant. Therefore, even though sodium ions and potassium ions are both alkali metals, they cannot permeate the lithium ion permeable membrane 10. The lithium ion permeable membrane 10 allows lithium ions to permeate and blocks sodium ions and potassium ions.

Next, the lithium complex 12 diffuses from the first main surface 10p to the second main surface 10q inside the lithium ion permeable membrane 10 according to Fick's law. When it reaches the interface between the second main surface 10q and the second solution 24, the lithium complex 12 dissociates, and the lithium ions are quickly released from inside the lithium ion permeable membrane 10 to the second solution 24. Instead of releasing lithium ions, the lithium extractant receives protons and is regenerated. This reaction is represented by the reverse reaction of the above formula (3). The lithium extractant 14 that has received the protons diffuses inside the lithium ion permeable membrane 10 from the second main surface 10q to the first main surface 10p, and again functions as a carrier for capturing and releasing lithium ions.

The driving force of the above-mentioned transport phenomenon is presumed to result from the counter transport of protons. Therefore, the pH of the first solution 22 and the pH of the second solution 24 affect the recovery efficiency of lithium ions. Protons in the second solution 24 move to the first solution 22 and combine with hydroxide ions to generate water. Therefore, as the extraction of lithium ions progresses, the pH of the first solution 22 decreases and the pH of the second solution 24 increases. In order to suppress the decrease in the recovery efficiency of lithium ions, a treatment for adjusting the pH of the first solution 22 and the second solution 24 may be performed. Specifically, a necessary pH adjuster may be added to each of the first solution 22 and the second solution 24 as appropriate.

The lithium ion permeable membrane 10 of this embodiment blocks sodium ions and potassium ions and selectively allows lithium ions to pass through. In this sense, the lithium ion permeable membrane 10 can be a lithium separation membrane.

The technical meaning of "blocking sodium ions and potassium ions and selectively allowing lithium ions to pass" is as follows. That is, the amount of lithium ions passing from the alkaline aqueous solution to the acidic aqueous solution is at least twice the amount of sodium ions passing. Similarly, the amount of lithium ions passing from the alkaline aqueous solution to the acidic aqueous solution is at least twice the amount of potassium ions passing. When at least this level of selectivity can be achieved, it can be determined that sodium ions and potassium ions are blocked and lithium ions are selectively passing. The initial concentration of each ion in the alkaline aqueous solution is 500 mg/L. The initial pH of the alkaline aqueous solution is 11.5. The initial pH of the acidic aqueous solution is 1.5. The water temperatures are 25°C for each solution. The permeation time is 8 hours.

Figure 3 shows the manufacturing process for the lithium ion permeable membrane 10.

As shown in the mixing process in Figure 3, the polymer base material, lithium extractant, and solvent are mixed to prepare a raw material solution. The ratio of each component in the raw material solution is adjusted appropriately. A material that sufficiently dissolves the polymer base material is used as the solvent. For example, when cellulose is used as the polymer base material, a halogen solvent such as dichloromethane, N-methyl-2-pyrrolidone, N,N-dimethylformamide, 1,3-dioxolane, etc. can be used as the solvent.

Next, as shown in the molding process, the raw material solution is molded into a molded body of a predetermined shape. The molding method is not particularly limited, and an appropriate method is selected depending on the shape of the molded body to be obtained. For example, when a flat lithium ion permeable membrane 10 is required, a method of applying the raw material solution onto a support such as a glass plate to obtain a flat molded body (so-called casting method) can be used. When a hollow fiber-shaped lithium ion permeable membrane is required, a method of ejecting the raw material solution from a molding nozzle to obtain a hollow molded body can be used. The method of applying the raw material solution onto the support is also not particularly limited. Various application methods using a roll coater, inkjet, die coater, etc. can be used.

Next, as shown in the solidification process, the unsolidified molded body is brought into contact with the solvent extraction liquid. Typically, the molded body is immersed in the solvent extraction liquid. When producing a hollow fiber lithium ion permeable membrane, the hollow fiber molded body is directly fed from a molding nozzle toward the solvent extraction liquid. The solvent extraction liquid is a liquid in which the solvent contained in the raw material solution is soluble. The solvent extraction liquid is typically water. As the solvent is removed from the molded body, the molded body solidifies. Through the above processes, the lithium ion permeable membrane 10 is obtained.

The molding and solidification processes can be carried out continuously, for example, by a roll-to-roll membrane manufacturing method. Therefore, according to the method of this embodiment, it is possible to mass-produce large-area lithium ion permeable membranes 10.

The lithium ion permeable membrane 10 may be produced by a method utilizing phase separation of a polymer solution, such as thermally induced phase separation (TIPS) or non-solvent induced phase separation (NIPS). In addition, instead of the solidification process shown in FIG. 3, the solvent may be removed from the molded body by volatilizing the solvent in the air.

The lithium ion permeable membrane 10 is substantially non-porous. Therefore, the lithium extractant is less likely to dissolve into the solution. In other words, the lithium ion permeable membrane 10 has excellent durability.

Figure 4 is a schematic cross-sectional view of a lithium ion permeable membrane module 40. The lithium ion permeable membrane module 40 has a plurality of hollow fiber membranes 10k, a housing 43, a first inlet 43a, a first outlet 43c, a second inlet 43b, and a second outlet 43d. In this embodiment, the lithium ion permeable membrane module 40 is a hollow fiber membrane module. Each end of the plurality of hollow fiber membranes 10k is bundled by two casting parts 45. The plurality of hollow fiber membranes 10k are open at the end faces of the casting parts 45. The bundle of hollow fiber membranes 10k and the two casting parts 45 are housed in the housing 43.

In the lithium ion permeable membrane module 40, the first flow path 401 and the second flow path 402 are flow paths located inside the housing 43. The first flow path 401 is a flow path facing the first main surface of the lithium ion permeable membrane, i.e., the outer surface of the hollow fiber membrane 10k. The second flow path 402 is a flow path facing the second main surface of the lithium ion permeable membrane, i.e., the inner surface of the hollow fiber membrane 10k. In other words, a part of the second flow path 402 is formed by the tubular internal space of the hollow fiber membrane 10k. The first flow path 401 and the second flow path 402 are isolated from each other by the hollow fiber membrane 10k made of a lithium ion permeable membrane.

In the first flow path 401, for example, the first solution 22 described with reference to FIG. 2 flows. In the second flow path 402, for example, the second solution 24 described with reference to FIG. 2 flows. The first flow path 401 is connected to the first inlet 43a and the first outlet 43c. The second flow path 402 is connected to the second inlet 43b and the second outlet 43d. The first solution 22 flows into the first flow path 401 through the first inlet 43a and flows toward the first outlet 43c while contacting the outer surface of the hollow fiber membrane 10k. The second solution 24 flows into the second flow path 402 through the second inlet 43b and flows toward the second outlet 43d while contacting the inner surface of the hollow fiber membrane 10k. At this time, lithium ions move from the first solution 22 to the second solution 24, and protons move from the second solution 24 to the first solution 22.

The lithium ion permeable membrane module 40 of this embodiment can realize a flow process in which extraction and back-extraction are performed continuously and simultaneously. This makes it possible to recover lithium ions efficiently and quickly.

As can be understood by comparing FIG. 1 with FIG. 4, the first inlet 43a, the first outlet 43c, the second inlet 43b, and the second outlet 43d of the lithium ion permeable membrane module 40 are connected to the flow paths 2b, 2e, 2f, and 2c, respectively. In other words, the first solution 22 contains the permeate of the NF membrane module 30. The second solution 24 is a solution used to recover lithium ions. The first solution 22 may flow through the second flow path 402, and the second solution 24 may flow through the first flow path 401.

As protons move from the second solution 24 to the first solution 22, the pH of the first solution 22 gradually decreases and the pH of the second solution 24 gradually increases. Therefore, the permeation rate of lithium ions also gradually decreases, and the recovery efficiency of lithium ions decreases. To address this problem, for example, the pH of the first solution 22 and the pH of the second solution 24 may be monitored, and the flow rate of the first solution 22 in the first flow path 401 may be adjusted so that the pH of the first solution 22 and the pH of the second solution 24 are maintained within the desired range, and the flow rate of the second solution 24 in the second flow path 402 may be adjusted. By performing such flow rate control, it is possible to maintain the pH of the first solution 22 and the pH of the second solution 24 within the desired range. A flow type module such as a hollow fiber membrane module also has such an advantage.

The second solution 24 may be flowed through the first flow path 401, and the first solution 22 may be flowed through the second flow path 402. It is not necessary to continuously flow the first solution 22 and the second solution 24 through each flow path, and the first solution 22 and the second solution 24 may be intermittently supplied to the first flow path 401 and the second flow path 402, respectively, depending on the recovery speed of the lithium ions. In this case, the supply amount of the first solution 22 to the first flow path 401 may be adjusted, and the supply amount of the second solution 24 to the second flow path 402 may be adjusted so that the pH of the first solution 22 and the pH of the second solution 24 are maintained within the desired range.

The hollow fiber membrane 10k is obtained by pouring the formed body obtained by forming the raw material solution into a hollow shape directly into water and removing the solvent from the formed body.

The lithium ion permeable membrane module 40 is not limited to a hollow fiber membrane module. The lithium ion permeable membrane module 40 may be another type of membrane module, such as a spiral type, a pleated type (flat membrane type), or a tubular type. The lithium ion permeable membrane module 40 has the following advantages: (1) a flow process in which extraction and back-extraction are performed continuously and simultaneously can be realized, (2) a large membrane area can be secured even with a small installation area, and (3) expensive corrosion-resistant piping is not required. These advantages are not available in the solvent extraction method and adsorption method described above.

(System Operation)
As shown in FIG. 1, the raw solution is supplied to the NF membrane module 30 and filtered. The NF membrane module 30 separates monovalent ions and divalent ions. The concentrated solution of the NF membrane module 30 contains divalent ions such as Mg ²⁺ and SO ₄ ^2- . The permeated solution of the NF membrane module 30 contains monovalent ions such as Li ⁺ , Na ⁺ , and K ⁺ . Next, the permeated solution of the NF membrane module 30 is supplied to the first flow path 401 of the lithium ion permeable membrane module 40 through the flow path 2b. The lithium ions permeate the lithium ion permeable membrane 10 and move from the first solution flowing through the first flow path 401 to the second solution flowing through the second flow path 402. The sodium ions and potassium ions remain in the first solution. This allows only the lithium ions to be separated from the other ions and recovered.

The lithium ion recovery system 100 may include a pH adjuster 70. The pH adjuster 70 is connected to the flow path 2b through the flow path 2g. The pH adjuster 70 injects a pH adjuster into the permeate of the NF membrane module 30 so that the pH of the permeate of the NF membrane module 30 is alkaline. Examples of the pH adjuster include NaOH, KOH, and NH _3. This adjusts the pH to a level suitable for the lithium ion permeable membrane module 40. As a result, the recovery efficiency of lithium ions is improved. The pH adjuster may be a solid such as a powder, a gas, or a pre-prepared aqueous solution.

Second Embodiment
5 is a configuration diagram of a lithium ion recovery system according to a second embodiment of the present invention. The lithium ion recovery system 200 includes a lithium ion permeable membrane module 40 and a reverse osmosis membrane module 50. The lithium ion permeable membrane module 40 is a module having a lithium ion permeable membrane that selectively allows lithium ions to pass through a first solution. The reverse osmosis membrane module 50 is disposed downstream of the lithium ion permeable membrane module 40 so that a second solution containing lithium ions that have permeated the lithium ion permeable membrane module 40 is supplied to the reverse osmosis membrane module 50. In this specification, the "reverse osmosis membrane" is referred to as an "RO membrane".

The lithium ion permeable membrane module 40, the first solution, and the second solution are as described in the first embodiment with reference to Figures 2 to 4.

The RO membrane module 50 is a module that uses an RO membrane and blocks all types of solutes, including monovalent and divalent ions. In other words, the lithium ion recovery system 200 is also configured to separate and recover lithium ions from a raw solution that contains lithium ions and other metal ions. Considering that pressure must be applied to the supply solution to cause reverse osmosis, it is difficult to treat a solution with an excessively high ion concentration with the RO membrane module 50. According to this embodiment, the ion concentration is lowered in advance by the lithium ion permeable membrane module 40, so that the second solution containing lithium ions can be easily treated by the RO membrane module 50.

The original solution containing lithium ions and other metal ions is as described in the first embodiment.

The lithium ion permeable membrane module 40 and the RO membrane module 50 are connected in this order by the flow path 2c. The second outlet (permeation side outlet) of the lithium ion permeable membrane module 40 and the raw water inlet of the RO membrane module 50 are connected by the flow path 2c. The first inlet (supply side inlet) of the lithium ion permeable membrane module 40 is connected to the flow path 2b. The first outlet (supply side outlet) of the lithium ion permeable membrane module 40 is connected to the flow path 2e. The second inlet (permeation side inlet) of the lithium ion permeable membrane module 40 is connected to the flow path 2f. The concentrated water outlet of the RO membrane module 50 is connected to the flow path 2h. The permeated water outlet of the RO membrane module 50 is connected to the flow path 2f. The second outlet of the lithium ion permeable membrane module 40 is connected to the flow path 2c. Each of the flow paths 2b, 2c, 2e, 2f, and 2h is composed of one or more pipes. If necessary, pumps, valves, sensors, and other devices may be disposed in each of the flow paths 2b, 2c, 2e, 2f, and 2h. The flow paths 2b, 2c, 2e, 2f, and 2h may each have a buffer tank.

The flow path 2f connects the permeate outlet of the RO membrane module 50 and the second inlet of the lithium ion permeable membrane module 40. In other words, the flow path 2f is a circulation flow path that connects the permeate outlet of the reverse osmosis membrane module 50 and the second flow path 402 of the lithium ion permeable membrane module 40.

As described in the first embodiment with reference to FIG. 2, the first solution 22 in contact with the first main surface 10p of the lithium ion permeable membrane 10 is alkaline. The second solution 24 in contact with the second main surface 10q of the lithium ion permeable membrane 10 is acidic. Therefore, an acid and an alkali are required to operate the lithium ion recovery system 200. If the second solution 24 is highly acidic, it takes a long time to neutralize the lithium ions when they are precipitated in the form of lithium carbonate.

According to this embodiment, the permeate of the RO membrane module 50 is acidic. In other words, the RO membrane module 50 has the ability to concentrate the solution containing lithium ions while recovering acid in the permeate. This makes it possible to reduce the time required for the neutralization process and the cost of materials required for the neutralization process. The permeate of the RO membrane module 50 can be reused as a solution that can be used to recover lithium ions. By reusing the permeate, the actual amount of liquid (amount of the second solution) consumed in the operation of the lithium ion permeable membrane module 40 can be reduced.

(System Operation)
As shown in FIG. 5, the raw solution is supplied to the first flow path 401 of the lithium ion permeable membrane module 40. The lithium ions permeate the lithium ion permeable membrane 10 and move from the first solution flowing through the first flow path 401 to the second solution flowing through the second flow path 402. The other ions remain in the first solution. This allows only the lithium ions to be separated and recovered from the other ions. The second solution discharged from the second flow path 402 of the lithium ion permeable membrane module 40 is supplied to the RO membrane module 50 through the flow path 2c. The solution (second solution) containing lithium ions is concentrated by the RO membrane module 50. The concentrated solution containing lithium ions is sent to a predetermined post-treatment process through the flow path 2h. The permeate of the RO membrane module 50 is supplied to the second flow path 402 of the lithium ion permeable membrane module 40 as the second solution used to recover lithium ions.

The lithium ion recovery system 200 may further include a pH adjuster 72. The pH adjuster 72 serves to add a pH adjuster to the permeate of the RO membrane module 50 in order to increase the hydrogen ion concentration of the permeate. The pH adjuster 72 is connected to the flow path 2f through the flow path 2i. By injecting the pH adjuster into the permeate of the RO membrane module 50, the pH of the permeate is adjusted to a value suitable for the lithium ion permeable membrane module 40. As a result, the recovery efficiency of lithium ions is improved.

The pH adjuster includes at least one selected from the group consisting of _CO2 and HCl. The pH adjuster may be a solid such as a powder, a gas, or a pre-prepared aqueous solution. When _CO2 gas is used as the pH adjuster, the pH adjuster 72 may be a device for bubbling _CO2 gas into the permeate. For example, using _CO2 gas recovered from various exhaust gases can also contribute to the conservation of the global environment. Using _CO2 may prevent impurities from being mixed into the concentrated liquid.

The method of recovering lithium ions from the concentrated solution containing lithium ions is not particularly limited. For example, the concentrated solution may be heated to remove water, thereby causing precipitation or crystallization of lithium compounds such as lithium chloride and lithium carbonate. Lithium carbonate may be precipitated by bubbling _CO2 gas into the concentrated solution. Lithium hydrogen carbonate may be produced by bubbling _CO2 gas into the concentrated solution, and then the concentrated solution may be heated to cause precipitation of lithium carbonate.

Third Embodiment
6 is a configuration diagram of a lithium ion recovery system according to a third embodiment of the present invention. The lithium ion recovery system 300 is a combination of the lithium ion recovery system 100 of the first embodiment and the lithium ion recovery system 200 of the second embodiment. That is, the lithium ion recovery system 300 includes an NF membrane module 30, a lithium ion permeable membrane module 40, and an RO membrane module 50.

The lithium ion permeable membrane module 40 is disposed downstream of the NF membrane module 30 so that the permeate of the NF membrane module 30 is supplied to the NF membrane module 30. The RO membrane module 50 is disposed downstream of the lithium ion permeable membrane module 40 so that a solution (second solution) containing lithium ions that has permeated the lithium ion permeable membrane module 40 is supplied to the RO membrane module 50. The lithium ion recovery system 300 provides both the effects obtained in the lithium ion recovery system 100 of the first embodiment and the effects obtained in the lithium ion recovery system 200 of the second embodiment.

The lithium ion recovery system 300 further includes a liquid intake equipment 60. The liquid intake equipment 60 is equipment for supplying the raw solution to the lithium ion recovery system 300 from a solution source such as a storage tank, and includes elements such as a pump, piping, a valve, and a filter. The liquid intake equipment 60 may include the pretreatment device described above. The raw solution is supplied from the liquid intake equipment 60 to the NF membrane module 30 through the flow path 2a.

The lithium ion recovery system 300 further includes a precipitation tank 66. The concentrated solution from the RO membrane module 50 is supplied to the precipitation tank 66. The concentrated solution contains lithium ions at a high concentration. By adding a precipitating reagent to the concentrated solution, the lithium ions can be precipitated in the form of lithium _carbonate ( _Li2CO3 ). The precipitating reagent contains, for example, at least one of sodium carbonate and _CO2 . The precipitate of lithium carbonate is recovered through the recovery path 4a.

The lithium ion recovery system 300 further includes _CO2 separation membrane modules 62a and 62b. The _CO2 separation membrane module 62a processes the exhaust gas from the exhaust gas source 64 to extract _CO2 gas. The _CO2 gas is blown as a pH adjuster into the permeate of the RO membrane module 50 through the flow path 3a. That is, the _CO2 separation membrane module 62a also plays a role as a pH adjuster. The _CO2 separation membrane module 62b also processes the exhaust gas from the exhaust gas source 64 to extract _CO2 gas. The _CO2 gas is introduced into the precipitation tank 66 as a precipitation reagent through the flow path 3b.

The lithium ion recovery system 300 further includes a valuable material recovery device 68. The recovery device 68 is supplied with the concentrated solution of the NF membrane module 30 through the flow path 2d. The recovery device 68 is also supplied with the first solution discharged from the first flow path 401 of the lithium ion permeable membrane module 40 through the flow path 2e. The concentrated solution of the NF membrane module 30 contains ions such as Mg ²⁺ and SO ₄ ^2- . The first solution discharged from the first flow path 401 of the lithium ion permeable membrane module 40 contains ions such as Na ⁺ and K ⁺ . The recovery device 68 is a device for recovering valuable ions contained in these ions by methods such as precipitation, membrane separation, and centrifugation. The wastewater from the recovery device 68 is reinjected into the sea, a lake, underground, etc. through the flow path 2j.

(System Operation)
First, the raw solution is supplied to the NF membrane module 30 and filtered. The NF membrane module 30 separates monovalent ions and divalent ions. The concentrated solution of the NF membrane module 30 contains divalent ions such as Mg ²⁺ and SO ₄ ^2- . The permeated solution of the NF membrane module 30 contains monovalent ions such as Li ⁺ , Na ⁺ , and K ⁺ . Next, the permeated solution of the NF membrane module 30 is supplied to the first flow path 401 of the lithium ion permeable membrane module 40 through the flow path 2b. The lithium ions permeate the lithium ion permeable membrane 10 and move from the first solution flowing through the first flow path 401 to the second solution flowing through the second flow path 402. The sodium ions and potassium ions remain in the first solution.

The second solution discharged from the second flow path 402 of the lithium ion permeable membrane module 40 is supplied to the RO membrane module 50 through flow path 2c. The solution containing lithium ions (second solution) is concentrated by the RO membrane module 50. The concentrated lithium ion solution is sent to the settling tank 66 through flow path 2h. The permeate of the RO membrane module 50 is supplied to the second flow path 402 of the lithium ion permeable membrane module 40 as the second solution used to recover lithium ions.

The ion concentration of the raw solution at the inlet of the NF membrane module 30 is, for example, 40 wt%. The ion concentration of the permeate of the NF membrane module 30 is, for example, 35 wt%. The ion concentration of the solution discharged from the second flow path 402 of the lithium ion permeable membrane module 40 is, for example, less than 1 wt%. The ion concentration of the concentrated liquid of the RO membrane module 50 is, for example, 5%. The lithium ion recovery system 300 can efficiently recover lithium without relying on solar evaporation. Solar evaporation and the lithium ion recovery system 300 may be combined.

According to the lithium ion recovery systems 100, 200, and 300 of the embodiments described above, lithium ions can be recovered with high efficiency and with low environmental impact. Since large-scale salt fields are not required, the system requires a small area. The time required to recover lithium ions is also short. Most of the impurities can be removed by membrane separation, so the lithium ion concentrate contains few impurities. As a result, it is possible to produce lithium with high purity.

(Reference example)
A raw material solution containing 5 wt% cellulose triacetate (M300, manufactured by Eastman Co.), 4.7 wt% Cyanex923 (manufactured by Solvay, Cyanex is a registered trademark), 6.5 wt% 1,3-diphenyl-1,3-propanedione (manufactured by Tokyo Chemical Industry Co., Ltd.), and 83.8 wt% 1,3-dioxolane (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was prepared. Cyanex923 is a mixture containing multiple alkylphosphine oxides of C6 to C8. The raw material solution was applied onto a glass plate using a coating device. The thickness of the coating film was 150 μm. Then, the glass plate was immersed in water together with the coating film. This removed the solvent from the coating film, and the lithium ion permeable membrane of Example 1 was obtained. The dimensions of the lithium ion permeable membrane of Example 1 were 150 mm long x 150 mm wide x 0.01 mm thick. Using a film cutting tool, the obtained permeable membrane was processed into a circle with a diameter of 60 mm.

(Permeation experiment)
The lithium ion permeable membrane of the reference example was attached to the container described with reference to FIG. 2. An alkaline aqueous solution with a pH of 11.5 containing Li ⁺ and Na ⁺ at a concentration of 500 mg/L was placed in one part of the container. An acidic aqueous solution (hydrochloric acid) with a pH of 1.5 containing HCl at a concentration of 0.1 mol/L was placed in the other part of the container. The temperatures of the alkaline aqueous solution and the acidic aqueous solution were both 25° C., and the volumes of both were 150 mL. A circular area with a diameter of 35 mm of the permeable membrane was in contact with the alkaline aqueous solution and the acidic aqueous solution.

Samples were taken from the acidic aqueous solutions immediately after stirring each solution with a stirrer and after 8 hours had passed. The concentrations of Li ions and Na ions contained in the samples were measured by ion chromatography. The difference between the initial ion concentration and the ion concentration after 8 hours is shown in Table 2.

As shown in Table 2, the lithium ion concentration in the acidic aqueous solution increased over time. In other words, lithium ions moved from the alkaline aqueous solution to the acidic aqueous solution through the lithium ion permeable membrane. In contrast, the concentration of sodium ions hardly changed over time. In other words, sodium ions hardly permeated the lithium ion permeable membrane. The lithium ion permeable membrane of the reference example had the ability to separate lithium ions and sodium ions.

The present invention is useful for recovering lithium from solution.

2a, 2b, 2c, 2d, 2e, 2f, 2h, 2i, 2j, 3a, 3b Flow path 4a Recovery path 10 Lithium ion permeable membrane 10p First main surface 10q Second main surface 10k Hollow fiber membrane 12 Lithium complex (lithium extractant)
14 Lithium extractant 20 Container 22 First solution 23 Stirrer 24 Second solution 30 NF membrane module 40 Lithium ion permeable membrane module (hollow fiber membrane module)
43 Housing 43a First inlet 43b Second inlet 43c First outlet 43d Second outlet 45 Casting section 50 RO membrane module 60 Liquid intake equipment 62a, 62b CO ₂ separation membrane module 64 Exhaust gas source 66 Settling tank 68 Recovery device 70, 72 pH adjuster 100, 200, 300 Lithium ion recovery system 401 First flow path 402 Second flow path

Claims (16)

A nanofiltration membrane module for treating a solution containing lithium ions;
a lithium ion permeable membrane module disposed downstream of the nanofiltration membrane module so that a permeate of the nanofiltration membrane module is supplied thereto, the lithium ion permeable membrane module having a lithium ion permeable membrane that selectively allows the lithium ions to pass therethrough;
Equipped with
The lithium ion permeable membrane comprises a polymer substrate and a lithium extractant;
The lithium extractant contains at least one selected from the group consisting of phosphorus compounds having a P=O bond and β-diketones.
Lithium ion recovery system. the lithium ion permeable membrane module has a first flow path facing a first main surface of the lithium ion permeable membrane and a second flow path facing a second main surface of the lithium ion permeable membrane,
When the permeate of the nanofiltration membrane module is defined as a first solution, and the solution used for recovering the lithium ions is defined as a second solution,
The first solution flows through the first flow path;
The second solution flows through the second flow path.
The lithium ion recovery system according to claim 1 . The lithium ion permeable membrane module is further provided with a reverse osmosis membrane module arranged downstream of the lithium ion permeable membrane module so that the solution containing the lithium ions that has permeated the lithium ion permeable membrane module is supplied thereto.
The lithium ion recovery system according to claim 1 or 2. the lithium ion permeable membrane module has a first flow path facing a first main surface of the lithium ion permeable membrane and a second flow path facing a second main surface of the lithium ion permeable membrane,
The reverse osmosis membrane module further includes a circulation flow path connecting the permeate outlet of the reverse osmosis membrane module and the second flow path of the lithium ion permeable membrane module.
The lithium ion recovery system according to claim 3 . The reverse osmosis membrane module further includes a pH adjuster that adds a pH adjuster to the permeate to increase the hydrogen ion concentration of the permeate.
The lithium ion recovery system according to claim 4. The pH adjuster comprises at least one selected from the group consisting of _CO2 and HCl;
The lithium ion recovery system according to claim 5 . a lithium ion permeable membrane module having a lithium ion permeable membrane that selectively permeates lithium ions contained in the first solution;
a reverse osmosis membrane module disposed downstream of the lithium ion permeable membrane module so as to supply a second solution containing the lithium ions that have permeated the lithium ion permeable membrane module;
Equipped with
The lithium ion permeable membrane comprises a polymer substrate and a lithium extractant;
The lithium extractant contains at least one selected from the group consisting of phosphorus compounds having a P=O bond and β-diketones.
Lithium ion recovery system. the lithium ion permeable membrane module has a first flow path facing a first main surface of the lithium ion permeable membrane and a second flow path facing a second main surface of the lithium ion permeable membrane,
The first solution flows through the first flow path;
The second solution flows through the second flow path.
The lithium ion recovery system according to claim 7. The reverse osmosis membrane module further includes a circulation flow path connecting the permeate outlet of the reverse osmosis membrane module and the second flow path of the lithium ion permeable membrane module.
The lithium ion recovery system according to claim 8. The reverse osmosis membrane module further includes a pH adjuster that adds a pH adjuster to the permeate to increase the hydrogen ion concentration of the permeate.
The lithium ion recovery system according to claim 9. treating a solution containing lithium ions through a nanofiltration membrane;
treating the nanofiltration membrane permeate with a lithium ion permeable membrane that selectively permeates the lithium ions;
Including,
The lithium ion permeable membrane comprises a polymer substrate and a lithium extractant;
The lithium extractant contains at least one selected from the group consisting of phosphorus compounds having a P=O bond and β-diketones.
Lithium ion recovery methods. The lithium ion-containing solution that has permeated the lithium ion-permeable membrane is further treated with a reverse osmosis membrane.
The method for recovering lithium ions according to claim 11. The method further comprises supplying a permeate of the reverse osmosis membrane to the lithium ion permeable membrane as a solution used for recovering the lithium ions.
The method for recovering lithium ions according to claim 12. Further comprising adding a pH adjuster to the permeate of the reverse osmosis membrane to increase the hydrogen ion concentration of the permeate.
The method for recovering lithium ions according to claim 13. The pH adjuster comprises at least one selected from the group consisting of _CO2 and HCl;
The method for recovering lithium ions according to claim 14. treating the first solution containing lithium ions with a lithium ion permeable membrane that selectively allows lithium ions to pass therethrough;
treating the second solution containing the lithium ions that have permeated the lithium ion permeable membrane with a reverse osmosis membrane;
Including,
The lithium ion permeable membrane comprises a polymer substrate and a lithium extractant;
The lithium extractant contains at least one selected from the group consisting of phosphorus compounds having a P=O bond and β-diketones.
Lithium ion recovery methods.

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