Method and apparatus for recovering alkali metal ions and hydroxide ions

Abstract

The present invention relates to a method for recovering alkali metal ions and hydroxide ions from water being treated, the method including a nanofiltration step in which water being treated is separated using a nanofiltration membrane, the water being treated containing alkali metal ions and polyvalent ions, having a pH of 10 or higher, and having a hydroxide ion concentration (mol / L) lower than the sum of alkali metal ion concentrations (mol / L), the nanofiltration membrane being such that the difference between the glucose removal rate and the isopropyl alcohol removal rate is 40% or greater, the glucose removal rate being 70% or higher, and the magnesium sulfate removal rate being 95% or higher.

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for recovering alkali metal ions and hydroxide ions. [Background technology]

[0002] In recent years, the demand for mineral resources has expanded significantly in line with global industrial and economic development. Mineral resources are essential for a wide range of industries, including the semiconductor industry. Even if there are large reserves of mineral resources buried in the earth's crust, there are many resources that are technically difficult to extract as elements, and are not economically viable due to the high costs of mining and refining, or that are localized in specific regions.

[0003] On the other hand, environmental issues have also been receiving a lot of attention, and there is a desire to build a recycling-oriented society. In particular, the development of electric vehicles, as well as the motors and batteries used in them, has been accelerating due to the attention being paid to reducing carbon dioxide emissions. In particular, with regard to batteries, lithium-ion secondary batteries are expected to become the main battery for electric vehicles due to their energy density and light weight.

[0004] In particular, there is increasing demand for high-nickel (NMC811) cathode materials, which have higher energy density than the conventional NMC622 and NMC531, as cathode materials for lithium-ion secondary batteries.

[0005] The precursors used in producing cathode materials are nickel sulfate as the nickel source, cobalt sulfate as the cobalt source, and manganese sulfate as the manganese source. As for the lithium source, while conventional cathode materials (NMC622, NMC531, etc.) use lithium carbonate, high-nickel cathode materials require lithium hydroxide, which is why demand for lithium hydroxide is increasing.

[0006] Non-Patent Document 1 describes methods for producing lithium hydroxide, mainly refining from brine, refining from ore, and electrolysis of lithium sulfate.

[0007] One method of purifying lithium carbonate from brine is to add slaked lime to a slurry of lithium carbonate purified from brine and heat it to convert the lithium carbonate into lithium hydroxide, which is then precipitated and removed to purify the lithium carbonate.

[0008] One method of refining lithium ore is to calcinate the concentrate, roast it with sulfuric acid, and then leach it with water to remove impurities such as Si and Al, obtain a lithium sulfate solution, add slaked lime to remove impurities such as Fe, and then add more slaked lime and sodium hydroxide to crystallize and remove the sodium sulfate, after which the lithium hydroxide is crystallized and refined.

[0009] In the above method, some lithium is also removed at the same time as the impurities are precipitated and removed, posing a problem in terms of the lithium recovery rate.

[0010] Furthermore, lithium sulfate electrolysis poses problems such as reduced efficiency due to clogging of the ion exchange membrane and the burden on the equipment caused by the generated chlorine gas.

[0011] As a method for purifying lithium hydroxide without removing impurities by precipitation or electrolysis, membrane separation and purification of lithium hydroxide using ion exchange resins or chelating resins can be mentioned.

[0012] One possible method for using an ion exchange resin or a chelating resin is to purify lithium hydroxide by removing polyvalent anions such as sulfate ions and carbonate ions in the solution with a strongly basic ion exchange resin in the OH form, and then removing polyvalent cations such as aluminum ions with a chelating resin.

[0013] Furthermore, as a method using membrane separation, for example, Patent Document 1 discloses the use of a nanofiltration membrane to further purify a lithium hydroxide solution after electrolysis. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Japanese Patent Publication No. 2001-508925 [Non-patent literature]

[0015] [Non-Patent Document 1] Okubo, "Lithium Production Technology Overview - Current Status and Future Trends", Metal Resources Report ISSN 2432-3128, Japan Oil, Gas and Metals National Corporation, 19-03-vol.48 (2019) Summary of the Invention [Problem to be solved by the invention]

[0016] However, when purifying lithium hydroxide using a chelating resin, the typical use range for chelating resins is pH 3 to 10, and therefore they cannot adsorb polyvalent cations at pH levels above 10. To remove polyvalent cations, it is possible to use a strong acid cation exchange resin or a weak acid ion exchange resin instead of a chelating resin, but these resins have a lower selective adsorption capacity for polyvalent cations and lithium ions than chelating resins, resulting in a lower recovery rate of lithium ions.

[0017] Furthermore, Patent Document 1 discloses that lithium hydroxide can be selectively separated from polyvalent ions using a nanofiltration membrane from a lithium hydroxide solution obtained by electrolysis, but does not describe a method for recovering high-purity lithium hydroxide with a high recovery rate from a solution containing polyvalent ions and lithium using a nanofiltration membrane. In other words, there is a need for a method for recovering alkali metal ions and hydroxide ions with high purity and high efficiency using membrane separation from alkaline treatment water containing polyvalent ions and alkali metals.

[0018] Therefore, an object of the present invention is to provide a method for recovering alkali metal ions and hydroxide ions with high purity and efficiency using membrane separation from treated water having a pH of 10 or higher that contains alkali metal ions and polyvalent ions. [Means for solving the problem]

[0019] In order to achieve the above object, the present invention has the following configuration. [1] A nanofiltration process is included in which the treated water is separated using a nanofiltration membrane. The water to be treated contains alkali metal ions and polyvalent ions, has a pH of 10 or more, and has a hydroxide ion concentration (mol / L) lower than the sum of the alkali metal ion concentrations (mol / L); The nanofiltration membrane has a difference of 40% or more between the glucose removal rate when a 1000 mg / L glucose aqueous solution at pH 6.5 is passed through it at an operating pressure of 0.5 MPa, 25°C, and the isopropyl alcohol removal rate when a 1000 mg / L isopropyl alcohol aqueous solution at pH 6.5 is passed through it at an operating pressure of 0.5 MPa, 25°C, and the glucose removal rate is 70% or more, and a magnesium sulfate removal rate of 95% or more when a 2000 mg / L magnesium sulfate aqueous solution at pH 6.5 is passed through it at an operating pressure of 0.5 MPa, 25°C, and the A method for recovering alkali metal ions and hydroxide ions from water to be treated. [2] The recovery method described in [1] above, wherein the sum of the concentrations (mol / L) of alkali metal ions other than sodium ions and potassium ions in the treated water is at least one time the chloride ion concentration (mol / L), and the sum of the concentrations (mol / L) of alkali metal ions other than sodium ions and potassium ions is at least one time the sum of the sodium ion concentration (mol / L) and the potassium ion concentration (mol / L). [3] The recovery method according to [1] or [2] above, further comprising a circulation step of mixing the concentrated solution obtained in the nanofiltration step with the water to be treated, and a step of controlling the pH of the water to be treated to 10 or higher. [4] The method according to [3] above, wherein the step of controlling the pH of the water to be treated to 10 or higher comprises adding a hydroxide of a polyvalent cation or an organic base to the water to be treated. [5] The method for recovering a compound according to [4] above, wherein the hydroxide of the polyvalent cation is calcium hydroxide. [6] The recovery method according to [3] above, further comprising the step of adding dilution water to the water to be treated, wherein the dilution water is an aqueous solution having a pH of 10 or higher containing a hydroxide of a polyvalent cation or an organic base. [7] The recovery method according to any one of [3] to [6] above, further comprising a step of passing the concentrated solution through an ultrafiltration membrane. [8] The recovery method according to any one of [3] to [7] above, further comprising the step of contacting at least one of the water to be treated and the concentrate with an anion exchange resin and mixing it with the water to be treated. [9] The method according to any one of [1] to [8] above, wherein the difference between the magnesium sulfate rejection rate and the magnesium chloride rejection rate when a 2000 mg / L aqueous magnesium chloride solution at pH 6.5 is passed through the nanofiltration membrane at an operating pressure of 0.5 MPa, 25°C, and 20% or less, and the glucose rejection rate is 70% or more and 90% or less.

[10] The recovery method according to any one of the above [1] to [9], wherein the alkali metal ions include at least one selected from the group consisting of lithium ions, rubidium ions, cesium ions, and francium ions.

[11] An alkali metal hydroxide recovered from a solution containing alkali metal ions and hydroxide ions, which is recovered by the recovery method according to any one of [1] to

[10] above.

[12] A positive electrode material for a lithium ion battery, synthesized using the alkali metal hydroxide according to

[11] above, wherein the alkali metal hydroxide is lithium hydroxide.

[13] A nanofiltration means for separating the water to be treated by a nanofiltration membrane is provided. The water to be treated contains alkali metal ions and polyvalent ions, has a pH of 10 or more, and has a hydroxide ion concentration (mol / L) lower than the sum of the alkali metal ion concentrations (mol / L); The nanofiltration membrane has a difference of 40% or more between the glucose removal rate when a 1000 mg / L glucose aqueous solution at pH 6.5 is passed through it at an operating pressure of 0.5 MPa, 25°C, and the isopropyl alcohol removal rate when a 1000 mg / L isopropyl alcohol aqueous solution at pH 6.5 is passed through it at an operating pressure of 0.5 MPa, 25°C, and the glucose removal rate is 70% or more, and a magnesium sulfate removal rate of 95% or more when a 2000 mg / L magnesium sulfate aqueous solution at pH 6.5 is passed through it at an operating pressure of 0.5 MPa, 25°C, and the An apparatus for recovering alkali metal ions and hydroxide ions from treated water.

[14] The recovery device described in

[13] above, further comprising a circulation means for mixing the concentrated liquid obtained by the nanofiltration means with the water to be treated, and a means for permeating the concentrated liquid through an ultrafiltration membrane.

[15] The recovery device described in

[13] or

[14] above, further comprising a means for contacting at least one of the treated water and the concentrated liquid obtained by the nanofiltration means with an anion exchange resin and mixing it with the treated water. [Effects of the Invention]

[0020] According to the recovery method of the present invention, it is possible to recover alkali metal ions and hydroxide ions with high purity and high efficiency from water to be treated that contains alkali metal ions and polyvalent ions and has a pH of 10 or higher. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic flow diagram showing a recovery method according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic flow diagram showing a recovery method according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] The following describes in detail the embodiments of the present invention, but the present invention is not limited to the following description and can be modified and implemented as desired within the scope that does not deviate from the gist of the present invention.

[0023] (1) Method for recovering alkali metal ions and hydroxide ions The recovery method of the present invention is characterized by including a nanofiltration step in which treated water containing alkali metal ions and polyvalent ions, having a pH of 10 or higher, and having a hydroxide ion concentration (mol / L) lower than the sum of the alkali metal ion concentrations (mol / L) is separated using a nanofiltration membrane described below.

[0024] The water to be treated may contain at least alkali metal ions and one or more polyvalent ions. This allows the recovery method of the present invention to be suitably used as a method for recovering alkali metal ions and hydroxide ions from the water to be treated. Furthermore, since the permeate obtained by the recovery method of the present invention contains alkali metal ions and hydroxide ions, the method can also be suitably used as a method for recovering alkali metal hydroxides, such as lithium hydroxide, rubidium hydroxide, cesium hydroxide, and francium hydroxide.

[0025] Examples of alkali metal ions include lithium ions, sodium ions, potassium ions, rubidium ions, cesium ions, and francium ions. From the viewpoint of the value of the target to be recovered, the water to be treated preferably contains at least one ion selected from the group consisting of lithium ions, rubidium ions, cesium ions, and francium ions, and more preferably contains lithium ions.

[0026] "Polyvalent ions" refer to ions that have a valence of 2 or more in absolute value in a solution state, and are classified as, for example, negatively charged polyvalent anions and positively charged polyvalent cations. In the present invention, which aims to recover alkali metal ions and hydroxide ions with high purity, polyvalent ions are considered impurities.

[0027] Examples of polyvalent anions include sulfate ions, carbonate ions, and phosphate ions, and examples of polyvalent cations include cobalt ions, nickel ions, manganese ions, aluminum ions, manganese ions, iron ions, copper ions, and zinc ions.

[0028] In the recovery method of the present invention, the water to be treated preferably has a high hydroxide ion concentration (mol / L) from the perspective described below, and must have a pH of 10 or higher, but at the same time, the hydroxide ion concentration must be lower than the sum of the alkali metal ion concentrations (mol / L). As a result of extensive research, the inventors have found that, in the nanofiltration process, ions permeate the membrane while satisfying the electrically neutral condition, so that by making the hydroxide ion concentration lower than the alkali metal ion concentration, it is possible to allow hydroxide ions to permeate while suppressing the permeation of multivalent ions, which are impurities in the water to be treated.

[0029] The hydroxide ion concentration (mol / L) is preferably 1 / 2 or less, and more preferably 1 / 5 or less, of the total alkali metal ion concentration (mol / L).

[0030] When the water to be treated contains lithium ions as alkali metal ions, the lithium ion concentration in the water to be treated is preferably 0.5 mg / L or more and 10,000 mg / L or less. Having a lithium ion concentration in the water to be treated of 0.5 mg / L or more improves the efficiency of lithium ion recovery by membrane separation. Furthermore, having a lithium ion concentration in the water to be treated of 10,000 mg / L or less can suppress an increase in the osmotic pressure difference, improving the efficiency of membrane separation. The lithium ion concentration in the water to be treated is more preferably 10 mg / L or more and 8,000 mg / L or less, and even more preferably 100 mg / L or more and 6,000 mg / L or less.

[0031] When the water to be treated contains lithium ions as alkali metal ions, the lithium ion concentration in the water to be treated is 7.2 x 10 -5 The lithium ion concentration in the water to be treated is preferably 7.2 × 10 mol / L or more and 1.5 mol / L or less. -5mol / L or more, the efficiency of lithium ion recovery by membrane separation is improved. Also, by keeping the lithium ion concentration in the water to be treated at 1.5 mol / L or less, the increase in osmotic pressure difference can be suppressed, improving the efficiency of membrane separation. The lithium ion concentration in the water to be treated is 1.4 × 10 -3 The concentration is more preferably from 0.014 mol / L to 1.2 mol / L, and even more preferably from 0.014 mol / L to 0.86 mol / L.

[0032] The total concentration of alkali metal ions in the treated water is 2 x 10 -5 The total concentration of alkali metal ions in the water to be treated is preferably 2×10 mol / L or more and 3.0 mol / L or less. -5 By keeping the total alkali metal ion concentration in the water to be treated at 3.0 mol / L or more, the recovery efficiency of alkali metal ions by membrane separation is improved. Furthermore, by keeping the total alkali metal ion concentration in the water to be treated at 3.0 mol / L or less, the increase in osmotic pressure difference can be suppressed, and the efficiency of membrane separation is improved. The total is 1.4 × 10 -3 The concentration is more preferably from 0.014 mol / L to 2.4 mol / L, and even more preferably from 0.014 mol / L to 1.7 mol / L.

[0033] The hydroxide ion concentration in the treated water is 1.0 x 10 -4 The hydroxide ion concentration in the water to be treated is preferably 1.0×10 mol / L or more and 1.0 mol / L or less. -4 mol / L or more, the amount of alkali metal ions that can be recovered in the permeate in the nanofiltration process increases. Also, by keeping the hydroxide ion concentration in the treated water at 1.0 mol / L or less, deterioration of the nanofiltration membrane is suppressed, and the period during which filtration can be continued is extended. The hydroxide ion concentration in the treated water is 1.0 × 10 -3 mol / L or more 1.0×10 -1 mol / L or less is more preferable, and 1.0×10 -2 mol / L or more 1.0×10 -1 mol / L or less is more preferable.

[0034] In the recovery method of the present invention, the pH of the water to be treated is 10 or higher. A pH of 10 or higher sufficiently increases the concentration of hydroxide ions to be recovered in the water to be treated, thereby increasing the amount of alkali metal ions that can be recovered in the permeate in the nanofiltration step. From the above perspective, the pH of the water to be treated is preferably 11 or higher, and more preferably 12 or higher.

[0035] On the other hand, it is preferable that the pH of the water to be treated is 14 or less. When the pH of the water to be treated is 14 or less, deterioration of the nanofiltration membrane is suppressed, and the period during which filtration can be continued is extended. It is more preferable to maintain the pH of the water to be treated at 10 or more throughout the nanofiltration process, and even more preferable to maintain the pH at 10 or more and 14 or less.

[0036] When the alkali metal ions to be recovered are alkali metal ions other than sodium and potassium ions, the concentration of monovalent ions other than hydroxide ions, particularly chloride ions and / or sodium and potassium ions, is preferably lower than the concentration of the alkali metal ions other than sodium and potassium ions to be recovered. Specifically, the concentration (mol / L) of alkali metal ions other than sodium and potassium ions in the water to be treated is preferably at least 1 time, and more preferably at least 10 times, the chloride ion concentration (mol / L). Furthermore, the concentration (mol / L) of alkali metal ions other than sodium and potassium ions in the water to be treated is preferably at least 1 time, and more preferably at least 10 times, the sum of the sodium ion concentration (mol / L) and the potassium ion concentration (mol / L). By satisfying the above-described relationships among the concentrations of alkali metal ions other than sodium and potassium ions, chloride ion concentration, sodium ion concentration, and potassium ion concentration in the water to be recovered, the alkali metal ions other than sodium and potassium ions and hydroxide ions to be recovered can be efficiently passed through the nanofiltration process. Furthermore, it is particularly preferable that the concentration (mol / L) of alkali metal ions other than sodium ions and potassium ions in the treated water is at least 1 time greater than both the chloride ion concentration (mol / L) and the sum of the sodium ion concentration (mol / L) and potassium ion concentration (mol / L).

[0037] (2) Nanofiltration process In the present invention, the water to be treated is treated with a nanofiltration membrane in the nanofiltration step, and alkali metal ions and hydroxide ions are separated and recovered on the permeate side.

[0038] (2-1) Nanofiltration membrane The nanofiltration membranes used in the present invention have fractionation properties that fall between those of reverse osmosis and ultrafiltration membranes. Reverse osmosis membranes, commonly known as reverse osmosis membranes, are capable of removing most organics and ions, whereas ultrafiltration membranes typically do not remove most ionic species and only remove high molecular weight organics.

[0039] In the recovery method of the present invention, in order to selectively permeate alkali metal ions and remove polyvalent ions, the nanofiltration step is carried out using a nanofiltration membrane that satisfies the following conditions: the difference between the glucose removal rate when a 1000 mg / L glucose aqueous solution at 25°C and pH 6.5 is passed through at an operating pressure of 0.5 MPa and the isopropyl alcohol removal rate when a 1000 mg / L isopropyl alcohol aqueous solution at 25°C and pH 6.5 is passed through at an operating pressure of 0.5 MPa is 40% or more, the glucose removal rate is 70% or more, and the magnesium sulfate removal rate when a 2000 mg / L magnesium sulfate aqueous solution at 25°C and pH 6.5 is passed through at an operating pressure of 0.5 MPa is 95% or more. Hereinafter, in this application, when simply referring to "glucose removal rate," it means the glucose removal rate when a 1000 mg / L aqueous glucose solution at 25°C and pH 6.5 is allowed to permeate at an operating pressure of 0.5 MPa; when referring to "isopropyl alcohol removal rate," it means the isopropyl alcohol removal rate when a 1000 mg / L aqueous isopropyl alcohol solution at 25°C and pH 6.5 is allowed to permeate at an operating pressure of 0.5 MPa; and when referring to "magnesium sulfate removal rate," it means the magnesium sulfate removal rate when a 2000 mg / L aqueous magnesium sulfate solution at 25°C and pH 6.5 is allowed to permeate at an operating pressure of 0.5 MPa.

[0040] Nanofiltration membranes with a glucose removal rate of 70% or more can selectively separate and recover alkali metal ions and polyvalent ions with high efficiency and over a long period of time, making them a highly efficient process. The glucose removal rate of nanofiltration membranes is preferably 80% or more. On the other hand, the glucose removal rate is preferably 90% or less. A glucose removal rate of 90% or less can increase the permeability of alkali metal ions. The glucose removal rate is preferably, for example, 70% or more and 90% or less.

[0041] For example, in a nanofiltration membrane, when the polyamide constituting the separation functional layer described below contains the substituted piperazine described below, the pore size of the separation functional layer is uniformly enlarged by the substituent of the substituted piperazine, making it possible to maintain a high magnesium sulfate removal rate while keeping the glucose removal rate at 90% or less.

[0042] Furthermore, by making the difference between the glucose removal rate and the isopropyl alcohol removal rate 40% or more, the selective separation of polyvalent ions and alkali metal ions can be improved. The difference between the glucose removal rate and the isopropyl alcohol removal rate is preferably 45% or more, and more preferably 50% or more. The difference between the glucose removal rate and the isopropyl alcohol removal rate refers to the value of the formula expressed as {(glucose removal rate) - (isopropyl alcohol removal rate)}.

[0043] The isopropyl alcohol rejection rate of the nanofiltration membrane is preferably 5% or more and 60% or less. From the viewpoint of polyvalent ion removal, the isopropyl alcohol rejection rate is preferably 5% or more, more preferably 10% or more. From the viewpoint of alkali metal ion permeability, the isopropyl alcohol rejection rate is preferably 60% or less, more preferably 50% or less.

[0044] A nanofiltration membrane with a magnesium sulfate rejection rate of 95% or more can efficiently suppress the permeation of polyvalent ions. From the viewpoint of more efficiently suppressing the permeation of polyvalent ions, the magnesium sulfate rejection rate is preferably 99.0% or more, and more preferably 99.2% or more. On the other hand, from the viewpoint of efficiently permeating alkali metal ions, the magnesium sulfate rejection rate is preferably 99.99% or less, and more preferably 99.90% or less.

[0045] Furthermore, it is preferable that the difference between the magnesium sulfate rejection rate and the magnesium chloride rejection rate when a 2000 mg / L magnesium chloride aqueous solution at pH 6.5 is passed through the nanofiltration membrane at an operating pressure of 0.5 MPa, 25°C, and pH 6.5 is 20% or less. The difference between the magnesium sulfate rejection rate and the magnesium chloride rejection rate refers to the value of the formula expressed as {(magnesium sulfate rejection rate) - (magnesium chloride rejection rate)}. Normally, the membrane surface of the separation functional layer of a nanofiltration membrane is negatively charged. However, when the difference between the magnesium sulfate rejection rate and the magnesium chloride rejection rate is 20% or less, the membrane surface charge approaches neutrality, making it difficult for polyvalent cations to pass through. On the other hand, the charge-neutral condition for anion permeation is satisfied, which promotes the permeation of alkali metal ions, allowing for more efficient separation of polyvalent cations and alkali metal ions.

[0046] The magnesium chloride rejection rate of the nanofiltration membrane is preferably 70% or more and 95% or less. From the viewpoint of selective separation of polyvalent ions and alkali metal ions, the magnesium chloride rejection rate is preferably 70% or more, more preferably 80% or more. From the viewpoint of alkali metal ion permeability, the magnesium chloride rejection rate is preferably 95% or less, more preferably 85% or less.

[0047] To separate alkali metal ions from polyvalent ions, the nanofiltration membrane preferably has a charge on the membrane surface, enabling both separation by pores (size separation) and electrostatic separation by charge. When the nanofiltration membrane satisfies the above conditions, both separation by pores and electrostatic separation by charge are possible.

[0048] Examples of materials for nanofiltration membranes include polymers such as cellulose acetate polymers, polyamides, sulfonated polysulfones, polyacrylonitrile, polyesters, polyimides, and vinyl polymers. Nanofiltration membranes may be composed of only one type of material, or may be composed of multiple materials. Furthermore, the structure of the nanofiltration membrane may be an asymmetric membrane having a dense layer on at least one side of the membrane and gradually increasing micropores in size from the dense layer toward the interior of the membrane or toward the other side, or a composite semipermeable membrane having a very thin separation functional layer made of a different material on top of the dense layer of the asymmetric membrane.

[0049] The composite semipermeable membrane is preferably, for example, a membrane having a porous support membrane containing polysulfone and a separation functional layer containing polyamide provided on the porous support membrane. The composite semipermeable membrane may also have a substrate in addition to the porous support membrane and the separation functional layer, in which case the porous support membrane is provided on at least one side of the substrate. The polyamide is a thin film formed on the porous support membrane by a polycondensation reaction between a polyfunctional aliphatic amine and a polyfunctional aromatic acid halide.

[0050] The separating functional layer in the composite semipermeable membrane preferably contains 50% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, of a semi-aromatic crosslinked polyamide obtained by interfacial polycondensation of a divalent or higher polyfunctional aliphatic amine compound and a divalent or higher polyfunctional aromatic acid halide, and particularly preferably consists of only a semi-aromatic crosslinked polyamide. By containing 50% by mass or more of a semi-aromatic crosslinked polyamide, excessive densification due to π-π interactions derived from the aromatic rings in the semi-aromatic crosslinked polyamide is suppressed, and excellent alkali metal ion permeability is achieved.

[0051] The polyfunctional aliphatic amine is preferably an alicyclic diamine, more preferably a 4,4'-bipiperidine or piperazine derivative.

[0052] The molecular weight of the alicyclic diamine is preferably 90 or more and 160 or less. When the molecular weight of the alicyclic diamine is 90 or more, the diffusion coefficient of the amine decreases, and polyamide is gradually formed during interfacial polycondensation. This facilitates the formation of a separation functional layer with uniform pore size in the film thickness direction from the early to middle stages of polycondensation. Furthermore, typically, during the early and final stages of polycondensation, excessive oligomers are formed on the support surface in contact with the organic layer, blocking the pores on the support surface and causing uneven pore size distribution in the film thickness direction. When the molecular weight of the alicyclic diamine is 160 or less, the molecular weight of the oligomers formed can be reduced, reducing their interaction with the semi-aromatic crosslinked polyamide. This facilitates the oligomers' detachment from the separation functional layer after the polycondensation reaction, facilitating the formation of a separation functional layer with uniform pore size in the film thickness direction.

[0053] Examples of alicyclic diamines having a molecular weight of 90 or more and 160 or less include substituted piperazines in which the piperazine ring is substituted with an alkyl group having 1 to 3 carbon atoms (e.g., 2-methylpiperazine, 2-ethylpiperazine, 2-normal propylpiperazine, 2,2-dimethylpiperazine, 2,2-diethylpiperazine, 2,3-dimethylpiperazine, 2,3-diethylpiperazine, 2,5-dimethylpiperazine, 2,5-diethylpiperazine, 2,6-dimethylpiperazine, 2,6-diethylpiperazine, and 2,3,5,6-tetramethylpiperazine), and homopiperazine.

[0054] The term "polyfunctional aromatic acid halide" refers to an aromatic acid halide having two or more halocarbonyl groups per molecule, and is not particularly limited as long as it produces a semi-aromatic crosslinked polyamide upon reaction with a polyfunctional aliphatic amine. Examples of polyfunctional aromatic acid halides that can be used include halides of 1,3,5-benzenetricarboxylic acid, 1,2,4-benzenetricarboxylic acid, 1,3-benzenedicarboxylic acid, 1,4-benzenedicarboxylic acid, 1,3,5-benzenetrisulfonic acid, and 1,3,6-naphthalenetrisulfonic acid. Among polyfunctional aromatic acid halides, acid chlorides are preferred, and from the viewpoints of economy, availability, ease of handling, ease of reactivity, etc., trimesoyl chloride, which is an acid halide of 1,3,5-benzenetricarboxylic acid, isophthaloyl chloride, which is an acid halide of 1,3-benzenedicarboxylic acid, terephthaloyl chloride, which is an acid halide of 1,4-benzenedicarboxylic acid, 1,3,5-benzenetrisulfonic acid chloride, which is an acid halide of 1,3,5-benzenetrisulfonic acid, and 1,3,6-naphthalenetrisulfonic acid chloride, which is an acid halide of 1,3,6-naphthalenetrisulfonic acid, are particularly preferred. The polyfunctional aromatic acid halides may be used alone or in combination of two or more. Among these, it is preferable to mix the trifunctional trimesic acid chloride, 1,3,5-benzenetrisulfonic acid chloride, or 1,3,6-naphthalenetrisulfonic acid chloride with either the bifunctional isophthalic acid chloride or terephthalic acid chloride, because this expands the intermolecular gaps in the crosslinked polyamide structure, allowing for the production of membranes with a uniform pore size distribution over a wide range. The molar ratio of the trifunctional acid chloride to the bifunctional acid chloride is preferably 1:20 to 50:1, and more preferably 1:1 to 20:1.

[0055] The composite semipermeable membrane can be obtained, for example, by forming a porous support membrane on a substrate, and then polycondensing a polyfunctional aliphatic amine and a polyfunctional aromatic acid halide on the porous support membrane to form a separation functional layer containing a semi-aromatic crosslinked polyamide. Furthermore, by adjusting the charge ratio of the polyfunctional aliphatic amine compound to the polyfunctional aromatic acid halide during polycondensation, the difference between the magnesium sulfate removal rate and the magnesium chloride removal rate can be adjusted. For example, by reducing the charge ratio of the polyfunctional aromatic acid halide to the polyfunctional aliphatic amine compound, the difference between the magnesium sulfate removal rate and the magnesium chloride removal rate can be reduced.

[0056] (2-2) Separation by nanofiltration membrane The nanofiltration membrane is preferably used in a state where it is incorporated into an element such as a spiral type.

[0057] In the nanofiltration step, the water to be treated is preferably supplied to the nanofiltration membrane at an operating pressure in the range of 0.1 MPa to 8 MPa. An operating pressure of 0.1 MPa or higher improves the membrane permeation rate, while an operating pressure of 8 MPa or lower can prevent damage to the nanofiltration membrane. The operating pressure is more preferably 0.5 MPa to 6 MPa, and even more preferably 1 MPa to 4 MPa.

[0058] In the nanofiltration process, the water to be treated is supplied to a nanofiltration membrane, and then a permeate and a concentrate are obtained. The permeate has a higher purity of alkali metal ions and hydroxide ions than the water to be treated, while the concentrate has a lower purity of alkali metal ions and hydroxide ions than the water to be treated. However, since the concentrate also contains a significant amount of alkali metal ions, it is preferable to provide a circulation process in which the concentrate obtained in the nanofiltration process is mixed with the water to be treated. By providing a circulation process, the recovery rate of alkali metal ions is improved. In this specification, the liquid obtained by mixing the concentrate with the water to be treated is also referred to as water to be treated.

[0059] When a circulation step is provided, the osmotic pressure of the water to be treated increases as the nanofiltration step progresses due to the concentration of polyvalent ions in the water. In this case, the operating pressure increases in the case of constant flow rate filtration, while the permeate flow rate decreases in the case of constant pressure filtration. Therefore, it is preferable to provide a step of adding dilution water to at least one of the water to be treated and the concentrate in response to the increase in the salt concentration of polyvalent ions and other substances in the water to be treated. The dilution water is not particularly limited, but examples include RO water, ion-exchange water, and alkaline aqueous solutions, each of which has a lower salt concentration than the water to be treated.

[0060] Furthermore, when the circulation step is provided, hydroxide ions permeate to the permeation side, which lowers the pH of the water to be treated. Therefore, from the viewpoint of improving the recovery efficiency of alkali metal ions, it is preferable to include a step of controlling the pH of the water to be treated to 10 or higher.

[0061] When a circulation step is provided, a method for controlling the pH of the water to be treated to 10 or higher may be, for example, a method in which a hydroxide of a polyvalent cation or an organic base is added to at least one of the water to be treated and the concentrate.

[0062] Examples of hydroxides of polyvalent cations include calcium hydroxide (hereinafter also referred to as "Ca(OH)"), magnesium hydroxide, aluminum hydroxide, iron hydroxide, copper hydroxide, zinc hydroxide, cobalt hydroxide, nickel hydroxide, manganese hydroxide, etc. Among these, calcium hydroxide is preferred because of its high solubility.

[0063] Examples of organic bases include primary amines such as ethylamine, diglycolamine, and ethylenediamine; secondary amines such as diethylamine and diethanolamine; tertiary amines such as dimethylethanolamine; quaternary ammonium salts such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, ethyltrimethylammonium hydroxide, benzyltrimethylammonium hydroxide, dimethylbis(2-hydroxyethyl)ammonium hydroxide, and choline; and heterocyclic amines such as pyrrole, piperidine, and 1,8-diazabicyclo[5.4.0]-7-undecene.

[0064] Furthermore, when a step of adding dilution water is also provided, it is preferable to use an aqueous solution having a pH of 10 or higher as the dilution water. By using an aqueous solution having a pH of 10 or higher as the dilution water, when the circulation step is carried out while adding dilution water and the nanofiltration step is carried out, the hydroxide ions that have permeated to the permeate side are replenished in the treated water, thereby maintaining the permeability of alkali metal ions and improving the recovery rate of alkali metal ions. The pH of the dilution water is preferably 11 or higher, and more preferably 12 or higher. On the other hand, it is preferable that the pH of the dilution water is 14 or lower.

[0065] The dilution water is more preferably an aqueous solution of pH 10 or higher in which a hydroxide of a polyvalent cation or an organic base is dissolved. When the counter cation of the hydroxide ion dissolved in the dilution water is a polyvalent cation, only hydroxide ions can be added to the water to be treated as the component that permeates the nanofiltration membrane, allowing efficient permeation of alkali metal ions in the water to be treated. The hydroxide of a polyvalent cation and the organic base dissolved in the dilution water are as described above.

[0066] The ratio of the permeate flow rate (L / min) to the concentrate flow rate (L / min) during the nanofiltration step is preferably permeate flow rate (L / min): concentrate flow rate (L / min) = 0.5:9.5 to 2:8, more preferably 0.8:9.2 to 1.5:8.5.

[0067] The permeation flux during the nanofiltration process is 0.1 m 3 / m 2 / d or more is preferable, and 0.2m 3 / m 2 On the other hand, the permeation flux is preferably 2.0 m / d or more. 3 / m 2 / d or less is preferable, and 1.5m 3 / m 2 It is more preferable that the permeation flux is 0.1 m / d or less. 3 / m 2 / d or more, alkali metal ions and hydroxide ions can be efficiently transmitted. 3 / m 2 / d or less, the amount of dilution water used for high recovery of alkali metal ions and hydroxide ions can be reduced.

[0068] Furthermore, the permeation flux is 0.1m 3 / m 2 / d or more and the concentrate flow rate is larger than the permeate flow rate, i.e., the linear velocity of the concentrate on the membrane surface is increased, thereby efficiently suppressing fouling due to precipitates on the membrane surface, as described below.

[0069] Furthermore, in order to improve the purity of alkali metal ions and hydroxide ions, the nanofiltration step may be carried out again using the permeate obtained in the nanofiltration step as the water to be treated.

[0070] For example, when recovering lithium ions and hydroxide ions, calcium ions (hereinafter referred to as "Ca 2+ ") concentration relative to the lithium ion (hereinafter referred to as "Li + ") concentration ratio (Li + / Ca 2+ ) and sulfate ions (hereinafter referred to as "SO4 2- ") concentration or carbonate ion (hereinafter "CO3 2- ) concentration relative to hydroxide ion (hereinafter referred to as "OH - ") concentration ratio {OH - / (SO4 2- or CO3 2- )} are the Li of the treated water, respectively. + / Ca 2+ , {OH - / (SO4 2- or CO3 2- )}, since lithium hydroxide can be recovered with high purity from the permeate, it is preferable that the ratio is 5 times or more, more preferably 6 times or more, and even more preferably 7 times or more.

[0071] (3) Ultrafiltration of concentrated liquid When a nanofiltration step including a circulation step is carried out, it is preferable to include a step of permeating the concentrate obtained in the nanofiltration step through an ultrafiltration membrane.

[0072] When the nanofiltration process including the circulation process is carried out, the concentration of polyvalent cations in the treated water or the concentrated solution increases, and the polyvalent cations and polyvalent anions (SO4 2- and CO3 2- In some cases, salts (polyvalent salts) of alkali metal ions (such as cations) may precipitate. Polyvalent salts are particularly likely to precipitate when polyvalent cations or dilution water containing polyvalent cations is added to the water to be treated. Therefore, in the circulation step, it is preferable to pass the concentrate obtained in the nanofiltration step through an ultrafiltration membrane and then mix it with the water to be treated. By continuing the nanofiltration step while removing the polyvalent salts precipitated in the concentrate using the ultrafiltration membrane, fouling of the nanofiltration membrane can be suppressed and alkali metal ions and hydroxide ions can be efficiently recovered.

[0073] Furthermore, by treating the concentrate rather than the water to be treated with the ultrafiltration membrane, the residual pressure of the concentrate flow can be used as the operating pressure for ultrafiltration.

[0074] (4) Treatment with anion exchange resin From the viewpoint of suppressing the precipitation of polyvalent salts as described in the above "(3) Treatment of the concentrated solution with an ultrafiltration membrane," when a nanofiltration process including a circulation process is carried out, it is also preferable to include a step of contacting at least one of the water to be treated and the concentrated solution obtained in the nanofiltration process with an anion exchange resin and mixing it with the water to be treated.

[0075] By contacting the treated water or the concentrate obtained in the nanofiltration process with an anion exchange resin, polyvalent anions (SO4 2- and CO3 2- The anion exchange resin adsorbs these ions, reducing their concentration and suppressing the precipitation of polyvalent salts. This suppression of polyvalent salt precipitation allows the nanofiltration process to continue while suppressing fouling of the nanofiltration membrane, enabling efficient recovery of alkali metal ions and hydroxide ions.

[0076] Although there are no particular limitations on the type of anion exchange resin, it is preferable to use a strongly basic anion exchange resin from the viewpoint of removing polyvalent anions. Furthermore, the anion exchange resin is preferably of the OH type from the viewpoint of efficiently supplying hydroxide ions that permeate the nanofiltration membrane together with the alkali metal ions to be recovered.

[0077] Methods for contacting the water to be treated or the concentrate with an anion exchange resin include adding the anion exchange resin to the target solution and passing the target solution through a fixed bed of anion exchange resin. Among these, passing the target solution through a fixed bed of anion exchange resin is preferred from the viewpoint of ease of handling the anion exchange resin. In the method for passing the target solution through a fixed bed of anion exchange resin, it is preferable to operate the SV value (= supply flow rate / filled volume), which is the ratio of the supply flow rate of the target solution to the fixed bed to the packed volume of the anion exchange resin in the fixed bed, within the range specified in the specifications for the anion exchange resin.

[0078] This step is preferably carried out in parallel with the nanofiltration step. By contacting the water to be treated or the concentrate with an OH-type anion exchange resin while carrying out the nanofiltration step, hydroxide ions released as polyvalent anions adsorb to the anion exchange resin can be passed through the nanofiltration membrane together with the alkali metal ions to be recovered, thereby suppressing excessive pH increases in the water to be treated and preventing deterioration of the nanofiltration membrane. When a treatment step using an anion exchange resin is carried out in parallel with the nanofiltration step, it is preferable to set the flow rate and SV value of the water to be treated or the concentrate supplied to the anion exchange resin so that the pH of the water to be treated is maintained at 10 or higher.

[0079] Once the concentration of polyvalent anions in the treated water falls below the concentration corresponding to the solubility of polyvalent anions in polyvalent salts (hereinafter referred to as "polyvalent anion solubility"), there is no need to further contact the water with the anion exchange resin. However, it is preferable to continue treatment with the anion exchange resin until the concentration falls below the polyvalent anion solubility.

[0080] If the fixed bed of the anion exchange resin breaks through during the nanofiltration process, it is preferable to regenerate the fixed bed with an alkali. There are no particular restrictions on the alkali used for regeneration, but aqueous sodium hydroxide or aqueous calcium hydroxide can be used. In preparation for breakthrough of the fixed bed of the anion exchange resin, it is preferable to prepare an identical fixed bed and use one fixed bed while regenerating the other.

[0081] (5) Method for recovering alkali metal hydroxide The alkali metal hydroxide can be recovered from the permeate containing alkali metal ions and hydroxide ions obtained by the above recovery method by crystallization or the like.

[0082] When recovering alkali metal hydroxides, the concentration (mg / L) of the alkali metal ions to be recovered contained in the permeate of the nanofiltration membrane is preferably 1 mg / L or more, more preferably 10 mg / L or more, and even more preferably 100 mg / L or more. A concentration of 1 mg / L or more improves the efficiency of precipitating the alkali metal hydroxides by crystallization or the like.

[0083] When the concentration (mg / L) of the alkali metal ions to be recovered contained in the nanofiltration membrane permeate is less than 1 mg / L, a concentration step for concentrating the obtained nanofiltration membrane permeate may be provided. The method for concentrating the permeate is not particularly limited, but examples thereof include concentration by evaporation and concentration using a reverse osmosis membrane.

[0084] Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, and francium hydroxide. Among these, from the viewpoint of the value of the object to be recovered, the alkali metal hydroxide preferably contains at least one selected from the group consisting of lithium hydroxide, rubidium hydroxide, cesium hydroxide, and francium hydroxide, and more preferably contains lithium hydroxide.

[0085] (6) Cathode materials for lithium-ion batteries When the alkali metal hydroxide obtained in the above-mentioned "(5) Method for recovering alkali metal hydroxide" is lithium hydroxide, this lithium hydroxide can be used to synthesize a positive electrode material for a lithium ion battery.

[0086] Conventional methods can be used to synthesize cathode materials for lithium-ion batteries. Examples include solid-state reaction, sol-gel, co-precipitation, hydrothermal, and spray pyrolysis. Among these, the conventional co-precipitation method is preferred (Schmuch R, Wagner R, Hoerpel G, Placke T, Winter M. 2018. Performance and cost of materials for lithium-based rechargeable automotive batteries. Nat Energy. 3(4):270).

[0087] Positive electrode materials include LMO, NCA, LNMO, LFP, LMFP, NMC111, NMC532, NMC622, and NMC811. Among these, the high-nickel NMC811 uses Li hydroxide instead of Li carbonate as a raw material, and therefore NMC811 is preferred as the positive electrode material in the present invention.

[0088] NMC811 is synthesized, for example, by the coprecipitation method described in the aforementioned publication. First, an aqueous solution of cobalt sulfate, nickel sulfate, a base (NaOH or Na2CO3), and a surfactant (NH4OH) is pumped into a continuous stirred tank reactor (CSTR), where the metal hydroxide or carbonate precipitates. After repeated filtration and washing to remove impurities, the material is dried, sieved, and mixed with a stoichiometric amount of lithium hydroxide. It is then calcined at 650-950°C to form NMC811.

[0089] (7) Recovery device The recovery device of the present invention is equipped with a nanofiltration means for separating water to be treated, which contains alkali metal ions and polyvalent ions, has a pH of 10 or higher, and has a hydroxide ion concentration (mol / L) lower than the sum of the alkali metal ion concentrations (mol / L), using a nanofiltration membrane in which the difference between the glucose removal rate when a 1000 mg / L glucose aqueous solution at 25°C and pH 6.5 is passed through at an operating pressure of 0.5 MPa and the isopropyl alcohol removal rate when a 1000 mg / L isopropyl alcohol aqueous solution at 25°C and pH 6.5 is passed through at an operating pressure of 0.5 MPa and the glucose removal rate is 70% or higher, and the magnesium sulfate removal rate when a 2000 mg / L magnesium sulfate aqueous solution at 25°C and pH 6.5 is passed through at an operating pressure of 0.5 MPa and the magnesium sulfate removal rate is 95% or higher.

[0090] The recovery device of the present invention has the above-described configuration, making it possible to recover alkali metal ions and hydroxide ions with high purity and high efficiency from treated water having a pH of 10 or higher that contains alkali metal ions and multivalent ions.

[0091] The water to be treated and the nanofiltration membrane are as described above in "(1) Method for recovering alkali metal ions and hydroxide ions" and "(2) Nanofiltration step."

[0092] The nanofiltration membrane is preferably packed in a pressure vessel in the form of a spiral element.

[0093] The recovery apparatus of the present invention preferably includes a circulation means for mixing the concentrated solution obtained by the nanofiltration means with the water to be treated. By including the circulation means, the recovery rate of alkali metal ions is improved.

[0094] The recovery device of the present invention preferably includes a means for adding dilution water to the water to be treated. By including the means for adding dilution water, an increase in the osmotic pressure of the water to be treated can be suppressed.

[0095] The recovery device of the present invention preferably includes the circulation means and a means for permeating the concentrated solution through an ultrafiltration membrane. The permeation means is more preferably provided in the circulation means. By including the permeation means, fouling of the nanofiltration membrane can be suppressed and alkali metal ions and hydroxide ions can be efficiently recovered.

[0096] The recovery device of the present invention preferably includes a means for bringing at least one of the water to be treated and the concentrate obtained by the nanofiltration means into contact with an anion exchange resin and mixing the resulting solution with the water to be treated. By including the means, fouling of the nanofiltration membrane can be suppressed and alkali metal ions and hydroxide ions can be efficiently recovered.

[0097] In order to achieve each of the above means, the recovery device of the present invention can be configured by selecting and combining pumps, piping, valves, tanks, vessels, temperature control devices, and instruments (pH meters, conductivity meters, flow meters, pressure meters, etc.) that are resistant to pH levels of 10 or higher in the water to be treated. [Example]

[0098] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Measurements in the examples and comparative examples were carried out as follows.

[0099] <Nanofiltration membrane performance> (Glucose removal rate and isopropyl alcohol removal rate of nanofiltration membrane) The isopropyl alcohol removal rate was calculated from the isopropyl alcohol concentrations in the permeate and feed water when a 1000 mg / L aqueous isopropyl alcohol solution at 25°C and pH 6.5 was passed through the nanofiltration membrane at an operating pressure of 0.5 MPa using the following formula (1). The glucose removal rate was calculated from the glucose concentrations in the permeate and feed water when a 1000 mg / L aqueous glucose solution at 25°C and pH 6.5 was passed through the nanofiltration membrane at an operating pressure of 0.5 MPa using the following formula (2). Isopropyl alcohol removal rate (%) = 100 × {1 - (isopropyl alcohol concentration in permeate water / isopropyl alcohol concentration in feed water)} Equation (1) Glucose removal rate (%) = 100 × {1 - (glucose concentration in permeate water / glucose concentration in feed water)} Equation (2)

[0100] The isopropyl alcohol concentration was determined using a gas chromatograph (GC-18A manufactured by Shimadzu Corporation), and the glucose concentration was determined using a refractometer (RID-6A manufactured by Shimadzu Corporation).

[0101] (Magnesium sulfate removal rate and magnesium chloride removal rate of nanofiltration membrane) A 2000 mg / L magnesium sulfate (hereinafter "MgSO4") aqueous solution at 25°C and pH 6.5 was used as feed water and passed through the nanofiltration membrane at an operating pressure of 0.5 MPa. The MgSO4 removal rate was calculated from the MgSO4 concentrations in the permeate and feed water using the following formula (3). Also, a 2000 mg / L magnesium chloride (hereinafter "MgCl2") aqueous solution at 25°C and pH 6.5 was used as feed water and passed through the nanofiltration membrane at an operating pressure of 0.5 MPa. The magnesium chloride removal rate was calculated from the MgCl2 concentrations in the permeate and feed water using the following formula (4). MgSO4 removal rate (%) = 100 × {1 - (MgSO4 concentration in permeate water / MgSO4 concentration in feed water)} Equation (3) MgCl2 removal rate (%) = 100 × {1 - (MgCl2 concentration in permeate water / MgCl2 concentration in feed water)} Equation (4)

[0102] The MgSO4 and MgCl2 concentrations were determined from the practical salinity, i.e., MgSO4 and MgCl2 concentrations, of the feed water and permeated water, measured by an electrical conductivity meter manufactured by Toa Denpa Kogyo Co., Ltd.

[0103] <Untreated water> Water to be treated a to g shown in Table 1 were prepared as follows.

[0104] [Table 1]

[0105] (Treated water a) Ca 2+ Concentration is 13mmol / L, Li + It was prepared by dissolving lithium sulfate, calcium sulfate, and calcium hydroxide in water to a concentration of 100 mmol / L and a pH of 12.0.

[0106] (Untreated water b) The water was prepared in the same manner as water a to be treated, except that lithium sulfate, calcium sulfate, and calcium hydroxide were dissolved in the water to achieve a pH of 11.

[0107] (Untreated water c) The water was prepared in the same manner as water to be treated a, except that lithium sulfate, calcium sulfate, and calcium hydroxide were dissolved in the water to adjust the pH to 12.4.

[0108] (Untreated water d) Li + The water was prepared in the same manner as water to be treated c, except that lithium sulfate, calcium sulfate, and calcium hydroxide were dissolved in water to a concentration of 10 mmol / L.

[0109] (Untreated water e) The water was prepared in the same manner as water to be treated a, except that lithium sulfate, calcium sulfate, and calcium hydroxide were dissolved in the water to adjust the pH to 9.5.

[0110] (Untreated water f) Ca 2+ Concentration is 13mmol / L, Li + It was prepared by dissolving lithium carbonate and calcium hydroxide in water to a concentration of 100 mmol / L and a pH of 12.4.

[0111] (g of treated water) The treated water was prepared in the same manner as for the treated water c, except that sodium chloride (hereinafter referred to as "NaCl") was dissolved so that the concentration was 200 mmol / L.

[0112] <Dilution water> Dilution water I to VI shown in Table 2 were prepared as follows.

[0113] [Table 2]

[0114] (Dilution water I) Water obtained by passing through a reverse osmosis membrane was used as is.

[0115] (Diluted Water II) Ca 2+ It was prepared by dissolving calcium hydroxide in water to a concentration of 12.6 mmol / L and a pH of 12.4.

[0116] (Diluted water III) Sodium ions (hereinafter referred to as "Na + ") was prepared by dissolving sodium hydroxide in water to a concentration of 25.1 mmol / L and a pH of 12.4.

[0117] (Diluted water IV) Ca 2+ It was prepared by dissolving calcium hydroxide in water to a concentration of 0.50 mmol / L and a pH of 11.

[0118] (Dilution water V) Ca 2+ It was prepared by dissolving calcium hydroxide in water to a concentration of 5.00 mmol / L and a pH of 12.

[0119] (Diluted water VI) Ca 2+ It was prepared by dissolving calcium hydroxide in water to a concentration of 0.016 mmol / L and a pH of 9.5.

[0120] <Nanofiltration membrane> (Nanofiltration membrane A) Nonwoven fabric made of polyester fiber (breathability 1cc / cm 2A 18.0 mass % dimethylformamide (DMF) solution of polysulfone was cast onto a substrate (semiconductor substrate) at 25°C to a thickness of 180 μm, and the substrate was immediately immersed in pure water and left for 5 minutes to produce a porous support membrane (thickness 160 μm) made of fiber-reinforced polysulfone.

[0121] Next, air adjusted to 25 ° C was blown to remove excess water, while adjusting the membrane surface temperature of the porous support membrane to 25 ° C. A 30 ° C aqueous solution containing 2.0 mass% piperazine, 250 mass ppm sodium dodecyl diphenyl ether disulfonate, and 1.0 mass% trisodium phosphate was applied to the surface of the porous support membrane and left to stand for 15 seconds, after which nitrogen was blown from an air nozzle to remove excess aqueous solution, forming a coating layer of amine aqueous solution on the porous support membrane. Furthermore, a 38 ° C n-decane solution containing 0.2 mass% trimesic acid chloride (hereinafter "TMC") was uniformly applied to the entire surface of the porous support membrane, and then interfacial polycondensation was performed by leaving it to stand for 1 minute at a relative humidity of 70% and a temperature of 25 ° C. Two fluids (pure water and air) were sprayed onto the membrane surface to remove the surface solution. Then, it was washed with pure water at 80 ° C to obtain nanofiltration membrane A.

[0122] (Nanofiltration membrane B) Nanofiltration membrane B was prepared in the same manner as nanofiltration membrane A, except that the piperazine was changed to 2,5-dimethylpiperazine, and a 38°C n-decane solution containing 0.2% by mass of TMC was uniformly applied to the entire surface of the porous support membrane, and then the membrane was left to stand at a relative humidity of 80% and 25°C for 1 minute.

[0123] (Nanofiltration membrane C) Nanofiltration membrane C was SelRO (registered trademark) MPS-34 manufactured by KOCH.

[0124] (Nanofiltration membrane D) Nanofiltration membrane D was obtained by producing a nanofiltration membrane in the same manner as nanofiltration membrane A, except that the TMC concentration was set to 0.5 mass %.

[0125] The membrane performance of nanofiltration membrane A, nanofiltration membrane B, nanofiltration membrane C, and nanofiltration membrane D is shown in Table 3.

[0126] [Table 3]

[0127] (Nanofiltration membrane spiral element) Using the above nanofiltration membranes A to D, an effective membrane area of ​​0.5 m 2 A spiral element with a diameter of 6.4 cm and a length of 30 cm was prepared. 3 / m 2 / d) is the permeate flow rate (m 3 / d) was divided by the effective membrane area.

[0128] <Permeate> After the nanofiltration process, the ion concentrations in the collected permeate were measured using an ICP emission spectrometer for cations and ion chromatography for anions. The hydroxide ion concentration was calculated using the following formula (5) by measuring the pH (hereinafter referred to as "P") of the permeate using a pH meter. Hydroxide ion concentration (mol / L) = 10^(14-P) Equation (5) The molar ratios were calculated from the obtained concentrations of each ion.

[0129] (Li + Recovery rate) Li + The recovery rate was calculated using the following formula (6). Li + Recovery rate (%) = W2 / W1 × 100 Equation (6) Where W1: Li in the water to be treated + Amount (g), W2: Li in permeate + The amounts (g) were calculated using the following formulas (7) and (8), respectively. W1 = volume of water to be treated (L) × Li in the water to be treated + Concentration (mg / L) Formula (7) W2 = Volume of permeate (L) × Li in permeate + Concentration (mg / L) Formula (8)

[0130] [Example 1] Using the configuration shown in Figure 1, a membrane element using nanofiltration membrane B was operated using crossflow filtration with 10 L of water to be treated c at 25°C under conditions of a permeate flow rate: concentrate flow rate = 1:9 and a permeate flow rate of 0.17 L / min. The permeate and the liquid obtained by permeating the concentrate through the ultrafiltration membrane were returned to the raw water tank containing the water to be treated c, and the operation was continued for 30 minutes to stabilize. Toray Industries, Inc.'s HFUG was used as the ultrafiltration membrane. The permeate was then discharged into the permeate tank, and dilution water II was added to the raw water tank from the dilution water tank at a flow rate of 0.17 L / min. After 10 hours, the supply of permeate to the permeate tank was stopped, and the addition of dilution water II was also stopped. The analysis results of the composition of the permeate discharged to the permeate tank are shown in Table 4. The Li of the permeate + Recovery rate, Li + / Ca 2+ , O.H. - / SO4 2- The results showed that lithium ions and hydroxide ions were highly purified and recovered at high yields. + / Na + and OH - / Cl - In the table, "-" means "cannot be calculated." + and Cl - was virtually undetectable.

[0131] [Example 2] The same method as in Example 1 was used, except that the treated water c was replaced with treated water f. The analysis results of the composition of the permeate are shown in Table 4. In this example, the polyvalent anions in the treated water were SO4 2- from CO3 2- The permeate has changed to Li + Recovery rate, Li + / Ca 2+ , O.H. - / CO3 2- The values ​​were high, and lithium ions and hydroxide ions were obtained with high purity and high recovery rates.

[0132] [Example 3] The procedure was the same as in Example 1, except that the water to be treated c was replaced with water to be treated b and the dilution water II was replaced with dilution water IV. Table 4 shows the analysis results of the composition of the permeate.

[0133] [Example 4] The procedure was the same as in Example 1, except that the water to be treated c was replaced with the water to be treated a, and the dilution water II was replaced with the dilution water V. Table 4 shows the analysis results of the composition of the permeate.

[0134] Comparing Examples 1, 3 and 4, the higher the pH of the treated water, the greater the amount of Li + Recovery rate, Li + / Ca 2+ , O.H. - / SO4 2- It can be seen that the recovery rate of lithium ions and hydroxide ions can be increased and the purity of lithium ions and hydroxide ions can be increased.

[0135] [Example 5] The same method as in Example 1 was carried out, except that the treated water c was replaced with treated water g. The analysis results of the composition of the permeate are shown in Table 4. When the NaCl concentration of the treated water was high, the NaCl concentration in the permeate was high. + and Cl - Li + and OH - Since it penetrated together with Li + / Na + , O.H. - / Cl - It can be seen that both decrease, that is, the purity decreases.

[0136] [Example 6] The same procedure as in Example 1 was carried out, except that the ratio of the permeate flow rate to the concentrate flow rate was 5:5. The analysis results of the permeate composition are shown in Table 4. When the concentrate flow rate was lowered, concentration polarization occurred on the membrane surface, resulting in the Li + / Ca 2+ It can be seen that is lower.

[0137] [Example 7] The same method as in Example 1 was used except that dilution water II was replaced with dilution water I. The analysis results of the composition of the permeate are shown in Table 4. When the pH of the dilution water is low, the pH of the water to be treated decreases over time. + It can be seen that the permeability of the catalyst decreases, and the recovery rate and purity of lithium ions and hydroxide ions both decrease.

[0138] [Example 8] The same procedure as in Example 1 was carried out except that dilution water II was replaced with dilution water III. The analysis results of the composition of the permeate are shown in Table 5. When an aqueous NaOH solution was used as the dilution water, the permeate contained Li. + Along with Na + is transmitted, and Li + The permeability of Li decreases + / Ca 2+ , Li + / Na + It can be seen that both decrease, that is, the purity decreases.

[0139] [Example 9] The same procedure as in Example 1 was carried out, except that nanofiltration membrane A was used instead of nanofiltration membrane B. The analysis results of the composition of the permeate are shown in Table 5. When nanofiltration membrane A, which has a particularly high glucose removal rate of over 90%, was used, Li + The permeability of Li decreases + / Ca 2+ has decreased.

[0140] [Example 10] The same method as in Example 1 was used except that no ultrafiltration membrane was used. However, because the operating pressure increased due to fouling caused by scale components during filtration, the operation was switched to constant pressure operation when the pressure reached 1.5 times the initial operating pressure, and filtration was continued. The analysis results of the permeate composition are shown in Table 5. In this example, unlike Example 1, no ultrafiltration membrane was used, and therefore the nanofiltration membrane became fouled with scale components generated during operation, reducing the amount of permeate and causing Li + The recovery rate decreased.

[0141] [Example 11] The same method as in Example 1 was carried out using the configuration shown in Figure 2, except that an ultrafiltration membrane was not used, a portion of the concentrate from the nanofiltration step was brought into contact with an OH-type strongly basic anion exchange resin, and dilution water II was replaced with dilution water I. The OH-type strongly basic anion exchange resin was Diaion SA10AOH from Mitsubishi Chemical Corporation, packed in a column at 2 L. The flow rate of the concentrate fed to the column was adjusted so that the pH of the solution in the raw water tank was 12 to 14. The analysis results of the composition of the permeate are shown in Table 5. In this example, an ultrafiltration membrane was not used and the pH of the dilution water was low, but by bringing a portion of the concentrate into contact with an anion exchange resin and mixing it with the water to be treated, the Li content of the permeate was reduced. + Recovery rate, Li + / Ca 2+ , O.H. - / SO4 2- The values ​​were high, and lithium ions and hydroxide ions were obtained with high purity and high recovery rates.

[0142] [Example 12] The same procedure as in Example 9 was carried out, except that nanofiltration membrane D was used instead of nanofiltration membrane A. The analysis results of the composition of the permeate are shown in Table 5. Even when nanofiltration membrane D, which has a larger difference in the magnesium sulfate removal rate and magnesium chloride removal rate compared to nanofiltration membrane A, was used, Li was still able to be recovered, but Ca was not. 2+ High permeability of Li + The permeability of Li decreases + / Ca 2+ was lower than in Example 9.

[0143] [Comparative Example 1] The same procedure as in Example 1 was carried out except that the treated water c was replaced with treated water e and the dilution water II was replaced with dilution water VI. The analysis results of the composition of the permeate are shown in Table 5. When the pH of the treated water was less than 10, Li + is almost impermeable, and Li + The recovery rate dropped significantly.

[0144] Comparative Example 2 The same method as in Example 1 was carried out, except that the treated water c was replaced with treated water d. The analysis results of the composition of the permeate are shown in Table 5.+ OH than concentration - Because of its high concentration, Ca 2+ The permeability of Li in the permeate is high. + / Ca 2+ was significantly lower.

[0145] Comparative Example 3 The same procedure as in Example 1 was carried out except that nanofiltration membrane B was replaced with nanofiltration membrane C. The analysis results of the composition of the permeate are shown in Table 5. Nanofiltration membrane C had a low MgSO4 removal rate, so Ca 2+ The permeability of Li in the permeate is high. + / Ca 2+ was significantly lower.

[0146] [Table 4]

[0147] [Table 5]

[0148] From the above results, it can be seen that Examples 1 to 12, which are the methods for recovering alkali metal ions and hydroxide ions of the present invention, can recover alkali metal ions, namely lithium ions and hydroxide ions, with higher purity and higher recovery rates than Comparative Examples 1 to 3. [Industrial Applicability]

[0149] By using the recovery method and recovery device of the present invention, it is possible to obtain, with a high recovery rate of lithium ions, an aqueous solution containing highly pure lithium ions and hydroxide ions suitable for producing, for example, lithium hydroxide needed for a cathode precursor for high-nickel lithium-ion batteries, which have seen increasing demand in recent years.

[0150] Although the present invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on a Japanese patent application (Patent Application No. 2023-169364) filed on September 29, 2023, the entire contents of which are incorporated by reference. [Explanation of symbols]

[0151] 1. Untreated water 2 Raw Water Tank 3 Nanofiltration membrane element 4 Permeate tank 5. Ultrafiltration membrane 6 Dilution water 7. Pump 8 Anion Exchange Resin

Claims

1. a nanofiltration step of separating the water to be treated using a nanofiltration membrane; a circulation step of mixing the concentrated liquid obtained in the nanofiltration step with the water to be treated; The method includes controlling the pH of the water to be treated to 10 or more, the water to be treated contains alkali metal ions and polyvalent ions, has a pH of 10 or more, and has a hydroxide ion concentration (mol / L) lower than the sum of alkali metal ion concentrations (mol / L); The nanofiltration membrane has a difference of 40% or more between the glucose removal rate when a 1000 mg / L aqueous glucose solution at pH 6.5 is passed through it at an operating pressure of 0.5 MPa, 25°C, and 25°C, and the isopropyl alcohol removal rate when a 1000 mg / L aqueous isopropyl alcohol solution at pH 6.5 is passed through it at an operating pressure of 0.5 MPa, 25°C, and 25°C, and the glucose removal rate is 70% or more; and the magnesium sulfate removal rate when a 2000 mg / L aqueous magnesium sulfate solution at pH 6.5 is passed through it at an operating pressure of 0.5 MPa, 25°C, and 25°C, and the magnesium sulfate removal rate is 95% or more. A method for recovering alkali metal ions and hydroxide ions from water to be treated.

2. 2. The method according to claim 1, wherein the sum of the concentrations (mol / L) of alkali metal ions other than sodium ions and potassium ions in the treated water is equal to or greater than the chloride ion concentration (mol / L), and the sum of the concentrations (mol / L) of alkali metal ions other than sodium ions and potassium ions is equal to or greater than the sum of the sodium ion concentration (mol / L) and the potassium ion concentration (mol / L).

3. 3. The method according to claim 1, wherein the step of controlling the pH of the water to be treated to 10 or higher comprises adding a hydroxide of a polyvalent cation or an organic base to the water to be treated.

4. 4. The method of claim 3, wherein the hydroxide of the polyvalent cation is calcium hydroxide.

5. 3. The recovery method according to claim 1, further comprising the step of adding dilution water to the water to be treated, wherein the dilution water is an aqueous solution containing a hydroxide of a polyvalent cation or an organic base and having a pH of 10 or higher.

6. The method according to claim 1 or 2, further comprising a step of passing the concentrated solution through an ultrafiltration membrane.

7. The recovery method according to claim 1 or 2, further comprising the step of contacting at least one of the water to be treated and the concentrate with an anion exchange resin and mixing the resin with the water to be treated.

8. 3. The method according to claim 1, wherein the difference between the magnesium sulfate rejection rate and the magnesium chloride rejection rate when a 2000 mg / L aqueous magnesium chloride solution having a pH of 6.5 and a temperature of 25°C is passed through the nanofiltration membrane at an operating pressure of 0.5 MPa is 20% or less, and the glucose rejection rate is 70% or more and 90% or less.

9. 3. The method according to claim 1, wherein the alkali metal ions include at least one selected from the group consisting of lithium ions, rubidium ions, cesium ions, and francium ions.

10. A recovery device used in the recovery method according to claim 1 or 2, A nanofiltration means for separating the water to be treated using the nanofiltration membrane; and a circulation means for mixing the concentrated liquid obtained by the nanofiltration means with the water to be treated.

11. 11. The recovery device of claim 10, further comprising means for permeating the concentrate through an ultrafiltration membrane.

12. The recovery apparatus according to claim 10, further comprising means for bringing at least one of the water to be treated and the concentrated liquid obtained by the nanofiltration means into contact with an anion exchange resin and mixing the resulting liquid with the water to be treated.

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