Method and device 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 to be treated, the method comprising a nanofiltration step for separating the water to be treated by means of a nanofiltration membrane, the water to be treated containing alkali metal ions and multivalent ions, having a pH of 10 or more, and having a hydroxide ion concentration (mol / L) lower than the total alkali metal ion concentration (mol / L). The difference between the glucose removal rate and the isopropanol removal rate of the nanofiltration membrane is 40% or more, the glucose removal rate is 70% or more, and the magnesium sulfate removal rate is 95% or more.

Description

Technical Field

[0001] This invention relates to a method and apparatus for recovering alkali metal ions and hydroxide ions. Background Technology

[0002] In recent years, with the development of the global industrial economy, the demand for mineral resources has expanded significantly. Among the mineral resources indispensable to a wide range of industries, especially the semiconductor industry, even those with large reserves buried in the earth's crust are technically difficult to extract individually, and the costs of mining and refining are high. There are also a large number of resources that are economically incalculable and those that exist locally in specific regions.

[0003] On the other hand, environmental issues are receiving increasing attention, with a desire to build a circular society. In particular, the focus on reducing carbon dioxide emissions has accelerated the development of electric vehicles, as well as the motors and batteries used in them. Specifically, regarding batteries, lithium-ion rechargeable batteries are expected to be the primary battery for electric vehicles due to their energy density and lightweight design.

[0004] Among them, as the cathode material for lithium-ion secondary batteries, the demand for high-nickel (NMC811) cathode materials with high energy density has increased compared to the previous NMC622 and NMC531.

[0005] Regarding the precursors used in the production of cathode materials, nickel sulfate is used as the nickel source, cobalt sulfate as the cobalt source, and manganese sulfate as the manganese source. However, for the lithium source, the previous cathode materials (NMC622, NMC531, etc.) used lithium carbonate, while high-nickel cathode materials require lithium hydroxide, thus increasing the demand for lithium hydroxide.

[0006] Non-patent document 1 describes a method for producing lithium hydroxide, which mainly involves purification from alkaline water, purification from ore, and electrolysis of lithium sulfate.

[0007] One method for purifying lithium carbonate from alkaline water is to add quicklime to the slurry of lithium carbonate being purified from alkaline water and heat it, thereby converting lithium carbonate into lithium hydroxide and precipitating out calcium carbonate for purification.

[0008] One method for purifying ore is to calcine the concentrate, roast it with sulfuric acid, and leach it with water to remove impurities such as Si and Al. After obtaining a lithium sulfate solution, quicklime is added to remove impurities such as Fe. Then, quicklime and sodium hydroxide are added to crystallize and remove the sodium sulfate, thereby crystallizing and purifying the lithium hydroxide.

[0009] In the above method, while removing the precipitate of impurities, a portion of lithium is also removed, resulting in a problem with the lithium recovery rate.

[0010] In addition, in the electrolysis of lithium sulfate, the efficiency reduction caused by the blockage of the ion exchange membrane and the load on the equipment caused by the generated chlorine gas become problems.

[0011] Methods for purifying lithium hydroxide without removing impurities by precipitation or by electrolysis include membrane separation, purification of lithium hydroxide using ion exchange resins or chelating resins.

[0012] As a method using ion exchange resins or chelating resins, one could consider using OH-type strong basic ion exchange resins to remove polyvalent anions such as sulfate or carbonate ions from the solution, and using chelating resins to remove polyvalent cations such as aluminum ions, thus purifying lithium hydroxide.

[0013] In addition, as a method of using membrane separation, for example, Patent Document 1 discloses a method of using a nanofiltration membrane to further purify the electrolyzed lithium hydroxide solution.

[0014] Existing technical documents

[0015] Patent documents

[0016] Patent Document 1: Japanese Patent Application Publication No. 2001-508925

[0017] Non-patent literature

[0018] Non-patent literature 1: Okubo, “An overview of lithium production technology – current status and future trends –” Metals Resources Report ISSN 2432-3128, Oil, Gas and Metals National Corporation, 19-03-vol.48 (2019). Summary of the Invention

[0019] The problem that the invention aims to solve

[0020] However, when using chelating resins to purify lithium hydroxide, the general operating range of chelating resins is between pH 3 and 10, meaning they cannot adsorb polyvalent cations at pH levels above 10. To remove polyvalent cations, strongly acidic cation exchange resins or weakly acidic ion exchange resins can be considered instead of chelating resins. However, compared to chelating resins, these resins have lower selective adsorption of polyvalent cations and lithium ions, resulting in lower lithium ion recovery rates.

[0021] Furthermore, Patent Document 1 discloses a method for selectively separating lithium hydroxide from a lithium hydroxide solution obtained by electrolysis using a nanofiltration membrane relative to multivalent ions, but it does not describe a method for recovering high-purity lithium hydroxide from a solution containing multivalent ions and lithium using a nanofiltration membrane with a high recovery rate. That is, it is desirable to use a method for high-purity and high-efficiency recovery of alkali metal ions and hydroxide ions from alkaline treated water containing multivalent ions and alkali metals using membrane separation.

[0022] Therefore, the object of the present invention is to provide a method for high-purity and high-efficiency recovery of alkali metal ions and hydroxide ions from treated water containing alkali metal ions and polyvalent ions at pH 10 or above by membrane separation.

[0023] Problem-solving methods

[0024] To achieve the above objectives, the present invention adopts the following approach.

[0025] [1]. A recovery method for recovering alkali metal ions and hydroxide ions from treated water, comprising a nanofiltration step of separating the treated water by a nanofiltration membrane.

[0026] The water being treated contains alkali metal ions and polyvalent ions, has a pH above 10, and has a hydroxide ion concentration (mol / L) lower than the sum of the alkali metal ion concentrations (mol / L).

[0027] The difference between the glucose removal rate when the nanofiltration membrane permeates a 1000 mg / L glucose aqueous solution at 25°C and pH 6.5 under an operating pressure of 0.5 MPa and the isopropanol removal rate when it permeates a 1000 mg / L isopropanol aqueous solution at 25°C and pH 6.5 under an operating pressure of 0.5 MPa is greater than 40%, the glucose removal rate is greater than 70%, and the magnesium sulfate removal rate when it permeates a 2000 mg / L magnesium sulfate aqueous solution at 25°C and pH 6.5 under an operating pressure of 0.5 MPa is greater than 95%.

[0028] [2]. In the recovery method described above [1], the total concentration (mol / L) of alkali metal ions other than sodium ions and potassium ions in the treated water is more than 1 times the concentration (mol / L) of chloride ions, and the total concentration (mol / L) of alkali metal ions other than sodium ions and potassium ions is more than 1 times the total concentration (mol / L) of sodium ions and potassium ions.

[0029] [3]. The recovery method described in [1] or [2] above further includes a circulation step of mixing the concentrate obtained from the nanofiltration step with the water to be treated, and a step of controlling the water to be treated at a pH of 10 or above.

[0030] [4]. The recycling method described above [3] includes the step of controlling the treated water to a pH of 10 or higher by adding a hydroxide of a polyvalent cation or an organic base to the treated water.

[0031] [5]. The recovery method described above [4] is calcium hydroxide, wherein the hydroxide of the polyvalent cation is calcium hydroxide.

[0032] [6]. The recovery method described in [3] above further includes the step of adding dilution water to the water to be treated, wherein the dilution water is an aqueous solution containing a hydroxide or organic base with a pH of 10 or higher.

[0033] [7]. The recovery method described in any of [3] to [6] above further includes the step of permeating the concentrate through an ultrafiltration membrane.

[0034] [8]. The recycling method described in any of [3] to [6] above further includes the steps of contacting at least one of the treated water and the concentrate with anion exchange resin and mixing with the treated water.

[0035] [9]. The difference between the magnesium sulfate removal rate of the nanofiltration membrane and the magnesium chloride removal rate when a 2000 mg / L magnesium chloride aqueous solution at 25°C and pH 6.5 is permeated under an operating pressure of 0.5 MPa is less than 20%, and the glucose removal rate is more than 70% and less than 90%.

[0036]

[10] . The recovery method described in any of [1] to [9] above, wherein the alkali metal ion comprises at least one selected from lithium ions, rubidium ions, cesium ions and francium ions.

[0037]

[11] . An alkali metal hydroxide, which is recovered from a solution containing alkali metal ions and hydroxide ions obtained by any of the recovery methods described in any of [1] to

[10] above.

[0038]

[12] . A positive electrode material for a lithium-ion battery, which is synthesized using the alkali metal hydroxide described in

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

[0039]

[13] . A recovery device for recovering alkali metal ions and hydroxide ions from water to be treated, comprising a nanofiltration unit for separating the water to be treated by a nanofiltration membrane.

[0040] The water being treated contains alkali metal ions and polyvalent ions, has a pH above 10, and has a hydroxide ion concentration (mol / L) lower than the sum of the alkali metal ion concentrations (mol / L).

[0041] The difference between the glucose removal rate when the nanofiltration membrane permeates a 1000 mg / L glucose aqueous solution at 25°C and pH 6.5 under an operating pressure of 0.5 MPa and the isopropanol removal rate when it permeates a 1000 mg / L isopropanol aqueous solution at 25°C and pH 6.5 under an operating pressure of 0.5 MPa is greater than 40%, the glucose removal rate is greater than 70%, and the magnesium sulfate removal rate when it permeates a 2000 mg / L magnesium sulfate aqueous solution at 25°C and pH 6.5 under an operating pressure of 0.5 MPa is greater than 95%.

[0042]

[14] . The recovery apparatus as described in

[13] above further includes a circulation unit for mixing the concentrate obtained through the nanofiltration unit with the water to be treated, and a unit for permeating the concentrate through an ultrafiltration membrane.

[0043]

[15] . The recovery apparatus as described in

[13] or

[14] above further includes a unit for contacting at least one of the treated water and the concentrate obtained through the nanofiltration unit with anion exchange resin and mixing it with the treated water.

[0044] Invention Effects

[0045] According to the recovery method of the present invention, alkali metal ions and hydroxide ions can be recovered with high purity and high efficiency from treated water containing alkali metal ions and polyvalent ions at a pH of 10 or higher. Attached Figure Description

[0046] Figure 1 This is a schematic flowchart illustrating a recycling method according to one embodiment of the present invention.

[0047] Figure 2 This is a schematic flowchart illustrating a recycling method according to another embodiment of the present invention. Detailed Implementation

[0048] The embodiments of the present invention are described in detail below, but the present invention is not limited to the following description. It can be implemented in any way without departing from the spirit of the present invention.

[0049] (1) Methods for recovering alkali metal ions and hydroxide ions

[0050] The recovery method of the present invention is characterized by comprising the following steps: 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 alkali metal ion concentrations (mol / L), is separated by passing it through a nanofiltration membrane as described later.

[0051] The treated water must contain at least alkali metal ions and one or more polyvalent ions. Therefore, the recovery method of the present invention is suitable for use as a method for recovering alkali metal ions and hydroxide ions from treated water. Furthermore, since the permeate obtained by the recovery method of the present invention contains alkali metal ions and hydroxide ions, it is also suitable for use as a method for recovering alkali metal hydroxides, such as lithium hydroxide, rubidium hydroxide, cesium hydroxide, francium hydroxide, etc.

[0052] 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 recovered material, the treated water preferably contains at least one selected from lithium ions, rubidium ions, cesium ions, and francium ions, and more preferably contains lithium ions.

[0053] "Multivalent ions" refer to ions with a valence of 2 or higher in solution, such as negatively charged multivalent anions and positively charged multivalent cations. In this invention, which aims to recover alkali metal ions and hydroxide ions with high purity, multivalent ions are considered impurities.

[0054] Examples of polyvalent anions include sulfate ions, carbonate ions, and phosphate ions. Examples of polyvalent cations include cobalt ions, nickel ions, manganese ions, aluminum ions, iron ions, copper ions, and zinc ions.

[0055] In the recovery method of this invention, from a viewpoint described later, the treated water preferably has a high hydroxide ion concentration (mol / L) and must have a pH above 10. Simultaneously, this hydroxide ion concentration must be lower than the sum of the concentrations of alkali metal ions (mol / L). The inventors conducted in-depth research and discovered that in the nanofiltration process, ions permeate the membrane while satisfying the electroneutrality condition. Therefore, the hydroxide ion concentration is lower than the alkali metal ion concentration, thereby enabling the permeation of hydroxide ions while suppressing the permeation of impurities, i.e., polyvalent ions, in the treated water.

[0056] The total concentration of hydroxide ions (mol / L) relative to the total concentration of alkali metal ions (mol / L) is preferably less than 1 / 2, and more preferably less than 1 / 5.

[0057] When the water to be treated contains lithium ions as an alkali metal ion, the lithium ion concentration in the water is preferably 0.5 mg / L to 10,000 mg / L. A lithium ion concentration of 0.5 mg / L or higher improves the recovery efficiency of lithium ion recovery via membrane separation. Furthermore, a lithium ion concentration of 10,000 mg / L or lower helps to suppress the increase in osmotic pressure difference, thereby improving the efficiency of membrane separation. A more preferred lithium ion concentration is 10 mg / L to 8,000 mg / L, and even more preferably 100 mg / L to 6,000 mg / L.

[0058] When the water to be treated contains lithium ions as an alkali metal ion, the preferred lithium ion concentration in the water is 7.2 × 10⁻⁶. -5 The concentration of lithium ions in the treated water is between 7.2 × 10⁻⁶ mol / L and 1.5 mol / L. -5 A lithium ion concentration of 1.5 mol / L or higher improves the efficiency of lithium ion recovery via membrane separation. Furthermore, maintaining a lithium ion concentration of 1.5 mol / L or lower in the treated water helps suppress the increase in osmotic pressure differential, thereby improving membrane separation efficiency. A more preferred lithium ion concentration in the treated water is 1.4 × 10⁻⁶ mol / L. -3 The concentration is above 1.2 mol / L, and more preferably above 0.014 mol / L and below 0.86 mol / L.

[0059] The sum of the concentrations of alkali metal ions in the water to be treated is preferably 2 × 10⁻⁶. -5 The concentration of alkali metal ions in the treated water is between 2 × 10⁻⁶ mol / L and 3.0 mol / L. -5 A concentration of mol / L or higher improves the membrane separation efficiency for alkali metal ion recovery. Furthermore, by ensuring the total concentration of alkali metal ions in the treated water is below 3.0 mol / L, the increase in osmotic pressure differential can be suppressed, further improving membrane separation efficiency. A more preferable total concentration is 1.4 × 10⁻⁶ mol / L. -3 The concentration is above 0.014 mol / L and below 2.4 mol / L, and more preferably above 0.014 mol / L and below 1.7 mol / L.

[0060] The preferred hydroxide ion concentration in the treated water is 1.0 × 10⁻⁶. -4 The concentration of hydroxide ions in the treated water is between 1.0 × 10⁻⁶ mol / L and above. -4 With a hydroxide ion concentration of 1.0 mol / L or higher, the amount of alkali metal ions that can be recovered from the permeate through nanofiltration increases. Furthermore, since the hydroxide ion concentration in the treated water is below 1.0 mol / L, the degradation of the nanofiltration membrane is suppressed, increasing the period during which filtration can continue. A hydroxide ion concentration of 1.0 × 10⁻⁶ is more preferably preferred.-3 mol / L or higher 1.0×10⁻ 1 Below mol / L, more preferably 1.0 × 10⁻⁶ -2 mol / L or higher 1.0×10 -1 Below mol / L.

[0061] In the recovery method of the present invention, the pH of the water to be treated is 10 or higher. Because the pH is 10 or higher, the concentration of hydroxide ions, the target for recovery, in the water to be treated becomes sufficiently high, increasing the amount of alkali metal ions in the permeate that can be recovered through the nanofiltration process. From this viewpoint, the pH of the water to be treated is preferably 11 or higher, and more preferably 12 or higher.

[0062] On the other hand, the pH of the water being treated is preferably 14 or lower. When the pH of the water being treated is 14 or lower, the deterioration of the nanofiltration membrane is suppressed, and the period during which filtration can continue is increased. Furthermore, it is more preferable to maintain the pH of the water being treated at 10 or higher through the nanofiltration process, and even more preferable to maintain the pH at 10 or higher and 14 or lower.

[0063] When the alkali metal ions to be recovered in the treated water are alkali metal ions other than sodium and potassium ions, it is preferable that the concentration of monovalent ions other than hydroxide ions, particularly chloride ions and / or sodium and potassium ions, is lower than the concentration of 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 treated water is preferably more than 1 times the concentration (mol / L) of chloride ions, more preferably more than 10 times. Furthermore, the concentration (mol / L) of alkali metal ions other than sodium and potassium ions in the treated water is preferably more than 1 times the sum of the concentrations (mol / L) of sodium ions and potassium ions, more preferably more than 10 times. By satisfying the above relationships among the concentrations of alkali metal ions other than sodium and potassium ions, chloride ions, sodium ions, and potassium ions in the treated water, the alkali metal ions other than sodium and potassium ions to be recovered in the nanofiltration process and hydroxide ions can be effectively passed through. Furthermore, it is particularly preferred that the concentration (mol / L) of alkali metal ions other than sodium and potassium ions in the water to be treated is more than 1 times that of chloride ions (mol / L) and the sum of sodium ions (mol / L) and potassium ions (mol / L).

[0064] (2) Nanofiltration process

[0065] In this invention, the water to be treated is treated via a nanofiltration process through a nanofiltration membrane, and alkali metal ions and hydroxide ions are separated and recovered from the permeation side.

[0066] (2-1) Nanofiltration membrane

[0067] The nanofiltration membrane used in this invention has separation characteristics between reverse osmosis membranes and ultrafiltration membranes. Membranes commonly referred to as reverse osmosis membranes can remove most organic matter and ions. On the other hand, ultrafiltration membranes typically do not remove most types of ions, but are capable of removing high molecular weight organic matter.

[0068] In the recovery method of the present invention, in order to selectively allow alkali metal ions to pass through and remove multivalent ions, a nanofiltration process is performed using a nanofiltration membrane that meets the following conditions: the difference between the glucose removal rate when passing through a 1000 mg / L glucose aqueous solution at 25°C and pH 6.5 under an operating pressure of 0.5 MPa and the isopropanol removal rate when passing through a 1000 mg / L isopropanol aqueous solution at 25°C and pH 6.5 under 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 passing through a 2000 mg / L magnesium sulfate aqueous solution at 25°C and pH 6.5 under an operating pressure of 0.5 MPa is 95% or more. In the future, when referred to simply as "glucose removal rate" in this application, it refers to the glucose removal rate when a 1000 mg / L glucose aqueous solution at 25°C and pH 6.5 is passed through the solution under an operating pressure of 0.5 MPa. When referred to as "isopropanol removal rate", it refers to the isopropanol removal rate when a 1000 mg / L isopropanol aqueous solution at 25°C and pH 6.5 is passed through the solution under an operating pressure of 0.5 MPa. When referred to as "magnesium sulfate removal rate", it refers to the magnesium sulfate removal rate when a 2000 mg / L magnesium sulfate aqueous solution at 25°C and pH 6.5 is passed through the solution under an operating pressure of 0.5 MPa.

[0069] Nanofiltration membranes, with a glucose removal rate of over 70%, can efficiently and sustainably perform selective separation and recovery of alkali metal ions and multivalent ions, making it a highly efficient process. The glucose removal rate of the nanofiltration membrane is preferably 80% or higher. On the other hand, a glucose removal rate of 90% or lower is preferred. A glucose removal rate of 90% or lower improves the permeability of alkali metal ions. For example, a glucose removal rate of 70% or higher and 90% or lower is preferred.

[0070] For example, in nanofiltration membranes, by containing substituted piperazines (described later) in the polyamide constituting the separation functional layer, the pore size of the separation functional layer is uniformly enlarged by the substituents of the piperazine, enabling a high magnesium sulfate removal rate to be maintained while achieving a glucose removal rate of less than 90%.

[0071] Furthermore, by ensuring that the difference between the glucose removal rate and the isopropanol removal rate is 40% or more, the selective separation of multivalent ions and alkali metal ions can be improved. The difference between the glucose removal rate and the isopropanol removal rate is preferably 45% or more, more preferably 50% or more. The aforementioned difference between the glucose removal rate and the isopropanol removal rate refers to the value expressed by the formula {(glucose removal rate) - (isopropanol removal rate)}.

[0072] The isopropanol removal rate of the nanofiltration membrane is preferably 5% or more and 60% or less. From the viewpoint of removal of multivalent ions, the isopropanol removal rate is preferably 5% or more, more preferably 10% or more. From the viewpoint of permeability of alkali metal ions, the isopropanol removal rate is preferably 60% or less, more preferably 50% or less.

[0073] Nanofiltration membranes achieve a magnesium sulfate removal rate of 95% or higher, effectively suppressing the permeation of multivalent ions. From the viewpoint of more effectively suppressing the permeation of multivalent ions, the magnesium sulfate removal rate is preferably 99.0% or higher, more preferably 99.2% or higher. On the other hand, from the viewpoint of allowing alkali metal ions to permeate effectively, the magnesium sulfate removal rate is preferably 99.99% or lower, more preferably 99.90% or lower.

[0074] Furthermore, the nanofiltration membrane preferably exhibits a magnesium sulfate removal rate that is less than 20% different from the magnesium chloride removal rate when a 2000 mg / L magnesium chloride aqueous solution at 25°C and pH 6.5 is permeated under an operating pressure of 0.5 MPa. The difference between the magnesium sulfate and magnesium chloride removal rates is expressed as {(magnesium sulfate removal rate) - (magnesium chloride removal rate)}. Typically, the separation functional layer of a nanofiltration membrane carries a negative charge, but when the difference between the magnesium sulfate and magnesium chloride removal rates is less than 20%, the membrane surface charge is closer to neutral, making it difficult for polyvalent cations to permeate. On the other hand, to meet the charged neutral condition for anion permeation and promote the permeation of alkali metal ions, the separation of polyvalent cations and alkali metal ions can be performed more effectively.

[0075] The magnesium chloride removal 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 removal rate is preferably 70% or more, more preferably 80% or more. From the viewpoint of permeability of alkali metal ions, the magnesium chloride removal rate is preferably 95% or less, more preferably 85% or less.

[0076] To separate alkali metal ions and multivalent ions, nanofiltration membranes are preferably charged on their surface, enabling both pore-based separation (size separation) and charge-based electrostatic separation. If the nanofiltration membrane meets the above conditions, it can perform both separation through pores and electrostatic separation by charge.

[0077] Examples of materials used for nanofiltration membranes include cellulose acetate polymers, polyamides, sulfonated polysulfones, polyacrylonitrile, polyesters, polyimides, and vinyl polymers. A nanofiltration membrane can be composed of only one material or multiple materials. Furthermore, the structure of the nanofiltration membrane can be an asymmetric membrane with a dense layer on at least one side and micropores with gradually increasing pore size from the dense layer towards the membrane interior or on the other side; or it can be a composite semi-permeable membrane with a very thin separation functional layer formed of other materials on the dense layer of the asymmetric membrane.

[0078] As a composite semipermeable membrane, a preferred embodiment is a membrane having a porous support membrane containing polysulfone and a separation functional layer containing polyamide disposed on the porous support membrane. Alternatively, in addition to the porous support membrane and the separation functional layer, the composite semipermeable membrane may also include a substrate, in which case the porous support membrane is disposed on at least one side of the substrate. The polyamide is a thin film formed on the porous support membrane through a polycondensation reaction of a polyfunctional aliphatic amine with a polyfunctional aromatic acid acyl halide.

[0079] The separation functional layer of the composite semi-permeable membrane preferably contains 50% by mass or more of a semi-aromatic crosslinked polyamide obtained by interfacial condensation of a divalent or higher polyfunctional aliphatic amine compound and a divalent or higher polyfunctional aromatic acid acyl halide. More preferably, it contains 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably consists only of semi-aromatic crosslinked polyamide. By containing 50% by mass or more of semi-aromatic crosslinked polyamide, excessive densification caused by π-π interactions from the aromatic rings in the semi-aromatic crosslinked polyamide can be suppressed, resulting in excellent alkali metal ion permeability.

[0080] The multifunctional aliphatic amine is preferably an alicyclic diamine, more preferably a 4,4'-bipiperidine or piperazine derivative.

[0081] Furthermore, the molecular weight of the alicyclic diamine is preferably 90 to 160. When the molecular weight of the alicyclic diamine is 90 or higher, the diffusion coefficient of the amine decreases, and polyamide gradually forms during interfacial polycondensation. Therefore, from the initial to the middle stage of polycondensation, it is easy to form a separation functional layer with uniform pore size in the film thickness direction. In addition, usually in the initial and final stages of polycondensation, due to the excessive formation of oligomers on the surface of the support in contact with the organic layer, the pores on the support surface are closed, which is the main reason for the non-uniform pore size distribution in the film thickness direction. When the molecular weight of the alicyclic diamine is 160 or lower, the molecular weight of the generated oligomers can be reduced, and the interaction with the semi-aromatic crosslinked polyamide can be reduced. Therefore, after the separation functional layer is formed in the polycondensation reaction, the oligomers can easily detach from the separation functional layer, and a separation functional layer with uniform pore size can easily be formed in the film thickness direction.

[0082] As alicyclic diamines with a molecular weight of 90 to 160, examples 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-n-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, 2,3,5,6-tetramethylpiperazine, or mesoporazine).

[0083] "Multifunctional aromatic acyl halides" refer to aromatic acyl halides that have two or more halogenated carbonyl groups in one molecule. There are no special restrictions as long as they can be reacted with multifunctional aliphatic amines to obtain semi-aromatic crosslinked polyamides. Examples of multifunctional aromatic acyl halides that can be used include halides such as 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 acyl halides, acyl chlorides are preferred, especially from the viewpoints of economy, availability, ease of operation, and reactivity. Pyromellitic trimethylolpropionate chloride as an acyl halide of 1,3,5-benzenetricarboxylic acid, isophthalic acid acyl chloride as an acyl halide of 1,3-benzenedicarboxylic acid, terephthalic acid acyl chloride as an acyl halide of 1,4-benzenetricarboxylic acid, 1,3,5-benzenetricarboxylic acid acyl chloride as an acyl halide of 1,3,5-benzenetricarboxylic acid, and 1,3,6-naphthalenetricarboxylic acid acyl chloride as an acyl halide of 1,3,6-naphthalenetricarboxylic acid are preferred. Polyfunctional aromatic acid acyl halides can be used alone or in mixtures of two or more. In this method, by mixing any one of the difunctional isophthalic acid chloride and terephthalic acid chloride with the trifunctional pyromellitic acid chloride, 1,3,5-benzenetrisulfonic acid chloride, and 1,3,6-naphthalenetrisulfonic acid chloride, the intermolecular gaps in the polyamide crosslinking structure are expanded, allowing for wide-range control of membranes with uniform pore size distribution, and is therefore preferred. The preferred molar ratio of trifunctional acyl chloride to difunctional acyl chloride is 1:20 to 50:1, more preferably 1:1 to 20:1.

[0084] The aforementioned composite semi-permeable membrane is obtained, for example, by forming a porous support membrane on a substrate, and then performing condensation polymerization of a multifunctional aliphatic amine and a multifunctional aromatic acid acyl halide on the porous support membrane to form a separation functional layer containing a semi-aromatic crosslinked polyamide. Furthermore, by adjusting the ratio of the multifunctional aliphatic amine compound to the multifunctional aromatic acid acyl halide added during condensation, the difference between the magnesium sulfate removal rate and the magnesium chloride removal rate can be adjusted. For example, by decreasing the ratio of the multifunctional aromatic acid acyl halide to the multifunctional aliphatic amine compound, the difference between the magnesium sulfate removal rate and the magnesium chloride removal rate can be reduced.

[0085] (2-2) Separation by nanofiltration membrane

[0086] Nanofiltration membranes are preferably used when assembled in components such as spirals.

[0087] In the nanofiltration process, the water to be treated is preferably supplied to the nanofiltration membrane at an operating pressure of 0.1 MPa to 8 MPa. If the operating pressure is 0.1 MPa or higher, the membrane permeation rate increases; if it is 8 MPa or lower, damage to the nanofiltration membrane can be suppressed. More preferably, the operating pressure is 0.5 MPa to 6 MPa, and even more preferably, 1 MPa to 4 MPa.

[0088] In the nanofiltration process, after the water to be treated is supplied to the nanofiltration membrane, permeate and 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. On the other hand, since the concentrate also contains a significant amount of alkali metal ions, a recycling process is preferably provided to mix the concentrate obtained in the nanofiltration process with the water to be treated. By providing a recycling process, the recovery rate of alkali metal ions is improved. Furthermore, in this specification, the liquid formed by mixing the concentrate with the water to be treated is also referred to as the water to be treated.

[0089] When a circulation process is set up, as the nanofiltration process proceeds, multivalent ions in the treated water are concentrated, thus increasing the osmotic pressure of the treated water. At this point, under constant flow filtration, the operating pressure increases; under constant pressure filtration, the permeate flow rate decreases. Therefore, it is preferable to include a process of adding dilution water to at least one of the treated water and the concentrate, based on the increase in the salt concentration of multivalent ions in the treated water. There are no particular limitations on the dilution water; examples include RO water with a lower salt concentration than the treated water, ion-exchange water, and alkaline aqueous solutions.

[0090] Furthermore, in the case of a circulating process, the pH of the treated water decreases because hydroxide ions permeate to the permeation side. Therefore, from the viewpoint of improving the recovery efficiency of alkali metal ions, it is preferable to include a process that controls the pH of the treated water to be above 10.

[0091] As a method for controlling the pH of the water to be treated to be above 10 when a circulating process is set up, one example is adding a hydroxide or organic base of a polyvalent cation to at least one of the water to be treated and the concentrate.

[0092] Examples of hydroxides that are polyvalent cations include calcium hydroxide (hereinafter also referred to as "Ca(OH)2"), magnesium hydroxide, aluminum hydroxide, iron hydroxide, copper hydroxide, zinc hydroxide, cobalt hydroxide, nickel hydroxide, and manganese hydroxide. Among these, calcium hydroxide, which has high solubility, is preferred.

[0093] Examples of organic bases include primary amines such as ethylamine, diethylene glycolamine, and ethylenediamine; secondary amines such as diethylamine and diethanolamine; tertiary amines such as dimethylethanolamine; tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, ethyltrimethylammonium hydroxide, benzyltrimethylammonium hydroxide, dimethylbis(2-hydroxyethyl)ammonium hydroxide, choline, pyrrole, piperidine, and heterocyclic amines such as 1,8-diazabicyclo[5.4.0]-7-undecene.

[0094] Furthermore, if a dilution water addition step is included, it is preferable to use an aqueous solution with a pH of 10 or higher as the dilution water. By using an aqueous solution with a pH of 10 or higher as the dilution water, a circulation process is performed simultaneously with the addition of the dilution water. This ensures that the amount of hydroxide ions that permeate to the permeation side during the nanofiltration process is 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, more preferably 12 or higher. On the other hand, the pH of the dilution water is preferably 14 or lower.

[0095] The dilution water is more preferably a hydroxide of polyvalent cations or an aqueous solution with a pH of 10 or higher containing dissolved organic bases. Since the antication of hydroxide ions dissolved in the dilution water is a polyvalent cation, it can be added only to the water being treated as a component permeating the nanofiltration membrane, effectively allowing the permeation of alkali metal ions from the water to proceed. The hydroxide of polyvalent cations and the organic base dissolved in the dilution water are as described above.

[0096] The ratio of permeate flow rate (L / min) to concentrate flow rate (L / min) during the nanofiltration process is preferably 0.5:9.5 to 2:8, more preferably 0.8:9.2 to 1.5:8.5.

[0097] In addition, the preferred permeation flux during the nanofiltration process is 0.1 m. 3 / m 2 / d or more, preferably 0.2m 3 / m 2 / d or more. On the other hand, the preferred permeation flux is 2.0m. 3 / m 2 / d or less, preferably 1.5m3 / m 2 / d or less. By making the permeation flux 0.1m 3 / m 2 A flow rate of over / d effectively allows alkali metal ions and hydroxide ions to permeate. The permeability is 2.0m. 3 / m 2 With a volume of less than 1 / d, the amount of dilution water used for high recovery of alkali metal ions and hydroxide ions can be reduced.

[0098] Furthermore, by setting the permeation flux to 0.1m 3 / m 2 With a flow rate of more than / d and a concentration flow rate that is greater than the permeate flow rate, the linear velocity of the concentration on the membrane surface is increased, which can effectively suppress fouling caused by precipitates on the membrane surface as described later.

[0099] In addition, to improve the purity of alkali metal ions and hydroxide ions, the permeate obtained from the nanofiltration process can be used as the treated water and the nanofiltration process can be repeated.

[0100] For example, in the case of recovering lithium ions and hydroxide ions, if lithium ions (hereinafter referred to as "Li") in the permeate... + The concentration of calcium ions (hereinafter referred to as "Ca") relative to the concentration of calcium ions (hereinafter referred to as "Ca") 2+ The ratio of concentration (Li) + / Ca 2+ ), and hydroxide ions (hereinafter referred to as "OH-") - The concentration of ) relative to sulfate ions (hereinafter referred to as "SO4") 2- Concentration or carbonate ions (hereinafter referred to as "CO3") 2- The ratio of OH- to (SO4) concentrations 2- or CO3 2- The Li / Ca ratios of the water being treated are denoted as )}. 2+ 、{OH - / (SO4) 2- or CO3 2- If the concentration of lithium hydroxide is more than 5 times that of the permeate, lithium hydroxide can be recovered from the permeate with high purity. Therefore, it is preferable to have a concentration of more than 6 times, and more preferably more than 7 times.

[0101] (3) Ultrafiltration membrane treatment of concentrate

[0102] When implementing a nanofiltration process that includes a circulation process, it is preferable to include a process that allows the concentrate obtained in the nanofiltration process to pass through an ultrafiltration membrane.

[0103] In nanofiltration processes that include a recirculation step, the concentration of polyvalent cations in the treated water or concentrate increases, and sometimes the concentration of polyvalent cations and polyvalent anions (SO4) in the treated water also increases. 2- or CO3 2- Salts (polyvalent salts) from alkali metal ions (e.g., polyvalent cations) precipitate out. Polyvalent salts are particularly prone to precipitation when polyvalent cations are added to the water being treated, or when dilution water containing polyvalent cations is added. Therefore, in the circulation process, it is preferable to pass the concentrate obtained from the nanofiltration process through an ultrafiltration membrane and then mix it with the water being treated. By continuing the nanofiltration process while removing the polyvalent salts precipitated from the concentrate using an ultrafiltration membrane, scaling on the nanofiltration membrane can be suppressed, and alkali metal ions and hydroxide ions can be effectively recovered.

[0104] In addition, by treating the concentrate with an ultrafiltration membrane instead of the water being treated, the residual pressure of the concentrate stream can be used as the operating pressure of the ultrafiltration.

[0105] (4) Treatment using anion exchange resin

[0106] Based on the viewpoint of suppressing the precipitation of polyvalent salts described in “(3) Ultrafiltration membrane treatment of concentrate” above, when implementing a nanofiltration process that includes a circulation process, it is preferable to include a process in which at least one of the water to be treated and the concentrate obtained from the nanofiltration process is contacted with an anion exchange resin and mixed with the water to be treated.

[0107] By contacting the treated water or concentrate obtained from a nanofiltration process with an anion exchange resin, polyvalent anions (SO42-) are exchanged. 2- or CO3 2- (e.g., ions) are adsorbed by the anion exchange resin, reducing their concentration and thus inhibiting the precipitation of polyvalent salts. By inhibiting the precipitation of polyvalent salts, the nanofiltration process can continue while suppressing fouling on the nanofiltration membrane, effectively recovering alkali metal ions and hydroxide ions.

[0108] There are no particular restrictions on the type of anion exchange resin, but from the viewpoint of removing polyvalent anions, a strongly basic anion exchange resin is preferred. Furthermore, from the viewpoint of effectively supplying hydroxide ions that permeate through the nanofiltration membrane along with the target alkali metal ions, the anion exchange resin is preferably of the OH type.

[0109] Examples of methods for contacting the water or concentrate to be treated with anion exchange resin include adding the anion exchange resin to the target solution and passing the target solution through a fixed bed of the anion exchange resin. From the viewpoint of the treatability of the anion exchange resin, passing the target solution through a fixed bed of the anion exchange resin is preferred. In the method of passing the target solution through a fixed bed of the anion exchange resin, it is preferable to operate within the range specified in the anion exchange resin's product manual, using the ratio of the supply flow rate of the target solution to the fixed bed to the packing volume of the anion exchange resin in the fixed bed, i.e., the SV value (= supply flow rate / packing volume).

[0110] This process is preferably performed in parallel with the nanofiltration process. By contacting the treated water or concentrate with the OH-type anion exchange resin during the nanofiltration process, polyvalent anions can be adsorbed onto the anion exchange resin, while the released hydroxide ions and the target alkali metal ions can pass through the nanofiltration membrane together. This can suppress excessive pH rise in the treated water and inhibit nanofiltration membrane degradation. When performing the treatment process using anion exchange resin in parallel with the nanofiltration process, it is preferable to set the flow rate and SV value of the treated water or concentrate supplied to the anion exchange resin to maintain the pH of the treated water above 10.

[0111] If the concentration of polyvalent anions in the water being treated is below the concentration of polyvalent anions equivalent to the solubility of polyvalent salts (hereinafter referred to as "polyvalent anion solubility"), then it is not necessary to continue contacting the water with the anion exchange resin. However, it is preferable to continue treatment with the anion exchange resin until the polyvalent anion solubility falls below the required level.

[0112] When the fixed bed of the anion exchange resin is damaged during the nanofiltration process, it is preferable to regenerate the fixed bed using an alkali. There are no particular restrictions on the alkali used for regeneration; aqueous solutions of sodium hydroxide or calcium hydroxide, etc., can be used. In the event of a damaged fixed bed of the anion exchange resin, it is preferable to prepare an identical fixed bed in advance and use another fixed bed during the regeneration of one.

[0113] (5) Methods for recovering alkali metal hydroxides

[0114] Alkali metal hydroxides can be recovered from the permeate containing alkali metal ions and hydroxide ions obtained by the above-mentioned recovery methods through crystallization or other means.

[0115] When recovering alkali metal hydroxides, the concentration (mg / L) of the target alkali metal ions 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 can improve the efficiency of alkali metal hydroxides during precipitation processes such as crystallization.

[0116] When the concentration (mg / L) of the target alkali metal ions in the permeate of the nanofiltration membrane is less than 1 mg / L, a concentration step can be included to concentrate the obtained permeate. There are no particular limitations on the method for concentrating the permeate; examples include concentration by evaporation and concentration by reverse osmosis membranes.

[0117] Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, and francium hydroxide. From the viewpoint of the value of the recovered material, the alkali metal hydroxide preferably contains at least one selected from lithium hydroxide, rubidium hydroxide, cesium hydroxide, and francium hydroxide, and more preferably contains lithium hydroxide.

[0118] (6) Positive electrode material of lithium-ion battery

[0119] In the case where the alkali metal hydroxide obtained in the above-mentioned "(5) method for recovering alkali metal hydroxides" is lithium hydroxide, the lithium hydroxide can be used to synthesize the positive electrode material of lithium-ion batteries.

[0120] Methods for synthesizing cathode materials for lithium-ion batteries can be employed using previously known methods. Examples include solid-state reaction, sol-gel, co-precipitation, hydrothermal, and spray pyrolysis. Among these, the previously known co-precipitation method is preferred (Schmuch R, Wagner R, Hoerpel G, Plack T, Winter M. 2018. Performance and cost of materials for lithium-based rechargeable automotive batteries. Nat Energy. 3(4): 270).

[0121] Cathode materials include LMO, NCA, LNMO, LFP, LMP, NMC111, NMC532, NMC622, NMC811, etc. Among them, the raw material for high-nickel NMC811 is not Li carbonate but Li hydroxide, so NMC811 is preferred as the cathode material of the present invention.

[0122] NMC811 is synthesized, for example, by the coprecipitation method described in the aforementioned literature. First, an aqueous solution of cobalt sulfate, nickel sulfate, alkali (NaOH or Na₂CO₃), and surfactant (NH₄OH) is fed into a continuous stirred tank reactor (CSTR) to precipitate metal hydroxides or carbonates. To remove impurities, the material is repeatedly filtered and washed, dried, sieved, and then mixed with a stoichiometric amount of lithium hydroxide. Finally, NMC811 is formed by calcination at 650–950 °C.

[0123] (7) Recycling device

[0124] The recovery apparatus of the present invention includes a nanofiltration unit for separating treated water by a nanofiltration membrane. The treated water 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). The difference between the glucose removal rate when the nanofiltration membrane passes through a 1000 mg / L glucose aqueous solution at 25°C and pH 6.5 under an operating pressure of 0.5 MPa and the isopropanol removal rate when passing through a 1000 mg / L isopropanol aqueous solution at 25°C and pH 6.5 under an operating pressure of 0.5 MPa is 40% or higher, the glucose removal rate is 70% or higher, and the magnesium sulfate removal rate when passing through a 2000 mg / L magnesium sulfate aqueous solution at 25°C and pH 6.5 under an operating pressure of 0.5 MPa is 95% or higher.

[0125] The recovery device of the present invention, having the above-described structure, is capable of recovering alkali metal ions and hydroxide ions with high purity and high efficiency from treated water containing alkali metal ions and polyvalent ions at a pH of 10 or higher.

[0126] Regarding the water being treated and the nanofiltration membrane, see the descriptions in “(1) Method for recovering alkali metal ions and hydroxide ions” and “(2) Nanofiltration process” above.

[0127] Nanofiltration membranes are preferably filled into the pressure vessel in the form of spiral elements.

[0128] The recovery apparatus of the present invention preferably includes a circulation unit for mixing the concentrate obtained from the nanofiltration unit with the treated water. By including the circulation means, the recovery rate of alkali metal ions is improved.

[0129] The recovery apparatus of the present invention preferably includes a unit for adding dilution water to the water being treated. By including the means of adding dilution water, the increase in osmotic pressure of the water being treated can be suppressed.

[0130] The recovery apparatus of the present invention preferably includes the above-described circulation unit and a unit for permeating the above-described concentrate through an ultrafiltration membrane. More preferably, the unit for permeation is included in the circulation unit. By including the unit for permeation, fouling on the nanofiltration membrane can be suppressed, and alkali metal ions and hydroxide ions can be effectively recovered.

[0131] The recovery apparatus of the present invention preferably includes a means for contacting at least one of the treated water and the concentrate obtained through the nanofiltration unit with the anion exchange resin and mixing it with the treated water. By providing the above means, fouling on the nanofiltration membrane can be suppressed, and alkali metal ions and hydroxide ions can be effectively recovered.

[0132] In order to achieve the above-mentioned means, the recycling device of the present invention can select pumps, piping, valves, tanks, containers, temperature regulators, and instruments (pH meters, conductivity meters, flow meters, pressure gauges, etc.) that are resistant to pH 10 or higher of the water to be treated, and can be combined arbitrarily.

[0133] Example

[0134] The following examples illustrate the present invention, but the invention is not limited to these examples. The measurements in the examples and comparative examples were performed as follows.

[0135] <Performance of nanofiltration membranes>

[0136] (Glucose removal rate and isopropanol removal rate of nanofiltration membrane)

[0137] The isopropanol removal rate is calculated using equation (1) based on the isopropanol concentrations in the permeate and supply water when a 1000 mg / L isopropanol aqueous solution at 25°C and pH 6.5, used as supply water, is passed through a nanofiltration membrane at an operating pressure of 0.5 MPa. The glucose removal rate is calculated using equation (2) based on the glucose concentrations in the permeate and supply water when a 1000 mg / L glucose aqueous solution at 25°C and pH 6.5, used as supply water, is passed through a nanofiltration membrane at an operating pressure of 0.5 MPa.

[0138] Isopropanol removal rate (%) = 100 × {1 - (isopropanol concentration in permeate water / isopropanol concentration in supply water)} ... Equation (1)

[0139] Glucose removal rate (%) = 100 × {1 - (glucose concentration in permeate water / glucose concentration in supply water)}... Equation (2)

[0140] In addition, the concentration of isopropanol was determined using a gas chromatograph (GC-18A manufactured by Shimadzu Corporation), and the concentration of glucose was determined using a refractometer (RID-6A manufactured by Shimadzu Corporation).

[0141] (Magnesium sulfate removal rate and magnesium chloride removal rate of nanofiltration membrane)

[0142] The MgSO4 removal rate is calculated using equation (3) below, based on the MgSO4 concentrations of the permeate and the supply water when a 2000 mg / L magnesium sulfate (hereinafter referred to as "MgSO4") aqueous solution at 25°C and pH 6.5, used as supply water, is passed through a nanofiltration membrane at an operating pressure of 0.5 MPa. Furthermore, the magnesium chloride removal rate is calculated using equation (4) below, based on the MgCl2 concentrations of the permeate and the supply water when a 2000 mg / L magnesium chloride (hereinafter referred to as "MgCl2") aqueous solution at 25°C and pH 6.5, used as supply water, is passed through a nanofiltration membrane at an operating pressure of 0.5 MPa.

[0143] MgSO4 removal rate (%) = 100 × {1 - (MgSO4 concentration in permeate water / MgSO4 concentration in supply water)} • Equation (3)

[0144] MgCl2 removal rate (%) = 100 × {1 - (MgCl2 concentration in permeate water / MgCl2 concentration in supply water)} • Equation (4)

[0145] In addition, the concentrations of MgSO4 and MgCl2 were determined by measuring the conductivity of the supply water and the permeate water using a conductivity meter manufactured by Toa Denpa Kogyo Co., Ltd., and calculated based on their respective applicable salinity, i.e., the concentrations of MgSO4 and MgCl2.

[0146] <The treated water>

[0147] The water to be treated, a to g, as recorded in Table 1 is prepared as follows.

[0148]

[0149] (Water being treated, a)

[0150] To make Ca 2+ Concentration of 13 mmol / L, Li + It is prepared by dissolving lithium sulfate, calcium sulfate, and calcium hydroxide in water at a concentration of 100 mmol / L and a pH of 12.0.

[0151] (Water being treated b)

[0152] Except for dissolving lithium sulfate, calcium sulfate, and calcium hydroxide in water and setting the pH to 11, it is prepared using the same method as the water being treated (a).

[0153] (Water being treated c)

[0154] Except for dissolving lithium sulfate, calcium sulfate, and calcium hydroxide in water and setting the pH to 12.4, the same method as that used for the water being treated (a) is employed.

[0155] (The water being treated, d)

[0156] In addition to dissolving lithium sulfate, calcium sulfate, and calcium hydroxide in water, it also makes Li + For concentrations other than 10 mmol / L, the same method as that used for the water being treated is employed.

[0157] (Water being treated e)

[0158] Except for dissolving lithium sulfate, calcium sulfate, and calcium hydroxide in water and setting the pH to 9.5, it is prepared using the same method as the water being treated (a).

[0159] (Water being treated f)

[0160] To make Ca 2+ Concentration of 13 mmol / L, Li + It is prepared by dissolving lithium carbonate and calcium hydroxide in water at a concentration of 100 mmol / L and a pH of 12.4.

[0161] (g of water to be treated)

[0162] Except for dissolving NaCl to make the sodium chloride (hereinafter referred to as "NaCl") concentration 200 mmol / L, it is prepared using the same method as the water being treated.

[0163] <Dilution Water>

[0164] The dilution waters I to VI described in Table 2 are prepared as follows.

[0165]

[0166] (Dilution water I)

[0167] Use the water obtained directly through the reverse osmosis membrane.

[0168] (Dilution Water II)

[0169] To make Ca 2+ It is prepared by dissolving calcium hydroxide in water at a concentration of 12.6 mmol / L and a pH of 12.4.

[0170] (Dilution Water III)

[0171] Sodium ions (hereinafter referred to as "Na") + It is prepared by dissolving sodium hydroxide in water at a concentration of 25.1 mmol / L and a pH of 12.4.

[0172] (Dilution water IV)

[0173] To make Ca 2+ It is prepared by dissolving calcium hydroxide in water at a concentration of 0.50 mmol / L and pH 11.

[0174] (Dilution water V)

[0175] To make Ca 2+ It is prepared by dissolving calcium hydroxide in water at a concentration of 5.00 mmol / L and pH 12.

[0176] (Dilution water VI)

[0177] To make Ca 2+ It is prepared by dissolving calcium hydroxide in water at a concentration of 0.016 mmol / L and a pH of 9.5.

[0178] <Nanofiltration Membrane>

[0179] (Nanofiltration membrane A)

[0180] Nonwoven fabric made of polyester fibers (air permeability 1cc / cm) 2 A 18.0% by mass dimethylformamide (hereinafter referred to as "DMF") solution of polysulfone is cast to a thickness of 180 μm at 25°C and immediately immersed in pure water for 5 minutes, thereby forming a porous support membrane (160 μm thick) composed of fiber-reinforced polysulfone.

[0181] Next, while blowing air adjusted to 25°C to remove excess moisture, the surface temperature of the porous support membrane was adjusted to 25°C. An aqueous solution at 30°C containing 2.0% by mass of piperazine, 250 ppm by mass of sodium dodecyl diphenyl ether disulfonate, and 1.0% by mass of trisodium phosphate was coated onto the surface of the porous support membrane. After standing for 15 seconds, nitrogen gas was sprayed from an air nozzle to remove excess aqueous solution, thereby forming an amine aqueous solution coating layer on the porous support membrane. Furthermore, a 38°C n-decane solution containing 0.2% by mass of trimesoyl chloride (hereinafter referred to as "TMC") was uniformly coated onto the entire surface of the porous support membrane. After standing for 1 minute at 70% relative humidity and 25°C, interfacial condensation was performed. Two fluids (pure water and air) were sprayed onto the membrane surface to remove the surface solution. Then, the membrane was washed with pure water at 80°C to obtain nanofiltration membrane A.

[0182] (Nanofiltration membrane B)

[0183] As piperazine, 2,5-dimethylpiperazine was used. A decane solution containing 0.2% by mass of TMC at 38°C was uniformly coated onto the entire surface of the porous support membrane. The membrane was then allowed to stand for 1 minute at 80% relative humidity and 25°C. Otherwise, nanofiltration membrane B was prepared using the same method as nanofiltration membrane A.

[0184] (Nanofiltration membrane C)

[0185] KOCH's SelRO (registered trademark) MPS-34 was used as nanofiltration membrane C.

[0186] (Nanofiltration membrane D)

[0187] Except that the TMC concentration was set to 0.5% by mass, the nanofiltration membrane was prepared using the same method as nanofiltration membrane A to obtain nanofiltration membrane D.

[0188] The membrane properties of nanofiltration membranes A, B, C, and D are shown in Table 3.

[0189]

[0190] (Nanofiltration membrane spiral element)

[0191] Using the nanofiltration membranes A to D described above, an effective membrane area of ​​0.5 m² is prepared. 2 A spiral element with a diameter of 6.4 cm and a length of 30 cm. Additionally, the transmission flux (m... 3 / m 2 / d) is the permeate flow rate (m) 3 It is calculated by dividing / d) by the effective membrane area.

[0192] <Permeable Fluid>

[0193] After the nanofiltration process is completed, the concentrations of each ion in the collected permeate are determined by ICP emission spectroscopy for cations and by ion chromatography for anions. The concentration of hydroxide ions is determined by measuring the pH of the permeate (hereinafter referred to as "P") using a pH meter and calculated by the following formula (5).

[0194] Hydroxide ion concentration (mol / L) = 10^(14-P)...Equation (5)

[0195] Calculate the molar ratios based on the obtained ion concentrations.

[0196] (Li) + Recovery rate

[0197] Li + The recovery rate is calculated using the following formula (6).

[0198] Li + Recovery rate (%) = W2 / W1 × 100... Equation (6)

[0199] Here, W1: Li in the water being treated + Amount (g), W2: Li in the permeate + The amount (g) is calculated using the following formulas (7) and (8).

[0200] W1 = Volume of water treated (L) × Li in the water treated + Concentration (mg / L) ... Equation (7)

[0201] W2 = Permeate volume (L) × Li in permeate + Concentration (mg / L) ... Equation (8)

[0202] [Example 1]

[0203] use Figure 1The structure shown, relative to 10L of treated water c at 25°C, was operated in a cross-flow filtration mode using a nanofiltration membrane element B, with a permeate flow rate: concentrate flow rate = 1:9 and a permeate flow rate of 0.17 L / min. The permeate and the liquid after the concentrate has passed through the ultrafiltration membrane were returned to the raw water tank containing the treated water c, and the operation was continued for 30 minutes to stabilize it. The ultrafiltration membrane used was the HFUG manufactured by Toray Industries, Inc. Then, while the permeate was discharged into the permeate tank, 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 into the permeate tank are shown in Table 4. The Li of the permeate... + Recovery rate, Li + / Ca 2+ OH- / SO4 2- The high purity of both lithium ions and hydroxide ions allows for high recovery rates. Additionally, in Table 4, Li... + / Na + and OH - / Cl - In this text, "-" indicates "cannot be calculated". This is because Na was practically undetectable in the permeate. + and Cl - .

[0204] [Example 2]

[0205] Except for converting the treated water c to treated water f, the same method as in Example 1 was used. The analytical results of the permeate composition are shown in Table 4. In this example, compared to Example 1, the polyvalent anions in the treated water decreased from SO42-. 2- Turn into CO3 2- But through the liquid Li + Recovery rate, Li + / Ca 2+ OH - / CO3 2- Both are high, enabling lithium ions and hydroxide ions to be recovered with high purity and high efficiency.

[0206] [Example 3]

[0207] Except for changing the treated water c to treated water b and dilution water II to dilution water IV, the same method as in Example 1 was used. The analytical results of the composition of the permeate are shown in Table 4.

[0208] [Example 4]

[0209] Except for changing the treated water c to treated water a and dilution water II to dilution water V, the procedure was carried out in the same manner as in Example 1. The analytical results of the composition of the permeate are shown in Table 4.

[0210] Comparing Examples 1, 3, and 4, it can be seen that the higher the pH of the treated water, the better the Li + Recovery rate, Li + / Ca 2+ OH - SO4 2- The higher the purity, the higher the recovery rate of lithium ions and hydroxide ions.

[0211] [Example 5]

[0212] Except for changing the treated water c to treated water g, the same method as in Example 1 was used. The analytical results of the permeate composition are shown in Table 4. When the NaCl concentration of the treated water is high, due to Na... + and Cl - With Li + and OH - They permeate together into the permeate, so Li + / Na + OH - / Cl - All of them are reduced, that is, reduced in purity.

[0213] [Example 6]

[0214] Except that the permeate flow rate: concentrate flow rate = 5:5, the same method as in Example 1 was used. The analytical results of the permeate composition are shown in Table 4. If the concentrate flow rate is reduced, it can be seen that due to concentration polarization at the membrane surface, the Li in the permeate... + / Ca 2+ reduce.

[0215] [Example 7]

[0216] Except for changing dilution water II to dilution water I, the same method as in Example 1 was used. The analytical results of the permeate composition are shown in Table 4. When the pH of the dilution water is low, the pH of the treated water decreases over time, therefore Li... + The permeability decreases, resulting in a reduction in the recovery rate and purity of lithium ions and hydroxide ions.

[0217] [Example 8]

[0218] Except for changing dilution water II to dilution water III, the same method as in Example 1 was used. The analytical results of the permeate composition are shown in Table 5. When NaOH aqueous solution was used as the dilution water, Na… + With Li+ Together they permeate into the permeate, Li + The permeability of Li is reduced, therefore Li + / Ca 2+ Li + / Na + All of them are reduced, that is, reduced in purity.

[0219] [Example 9]

[0220] Except for replacing nanofiltration membrane B with nanofiltration membrane A, the same method as in Example 1 was used. The analytical results of the permeate composition are shown in Table 5. When using nanofiltration membrane A, which has a particularly high glucose removal rate exceeding 90%, due to Li... + Reduced permeability of Li + / Ca 2+ reduce.

[0221] [Example 10]

[0222] Except for the absence of an ultrafiltration membrane, the same method as in Example 1 was employed. However, because the scale buildup during filtration increased the operating pressure, constant pressure operation was switched on when the pressure reached 1.5 times the initial operating pressure, and filtration continued. The analysis results of the permeate composition are shown in Table 5. In this example, since an ultrafiltration membrane was not used compared to Example 1, the scale generated during operation formed deposits on the nanofiltration membrane, reducing the permeate volume and Li + The recovery rate has decreased.

[0223] [Example 11]

[0224] by Figure 2 The structure shown does not use an ultrafiltration membrane. Instead, a portion of the concentrate from the nanofiltration process is contacted with an OH-type strong-base anion exchange resin, and dilution water II is changed to dilution water I. Otherwise, the same method as in Example 1 is used. The OH-type strong-base anion exchange resin is used by packing 2L of Mitsubishi Chemical Corporation's DIAIONSA10AOH into the chromatographic column. The supply flow rate of the concentrate to the chromatographic column is adjusted to make the pH of the solution in the original water tank 12-14. The analytical results of the permeate composition are shown in Table 5. In this example, an ultrafiltration membrane is not used, and the pH of the dilution water is low. However, by contacting a portion of the concentrate with the anion exchange resin and mixing it with the treated water, the Li of the permeate is improved. + Recovery rate, Li + / Ca 2+ OH - SO4 - Both are high, enabling lithium ions and hydroxide ions to be recovered with high purity and high efficiency.

[0225] [Example 12]

[0226] Except for replacing nanofiltration membrane A with nanofiltration membrane D, the same method as in Example 9 was used. The analytical results of the permeate composition are shown in Table 5. Compared to nanofiltration membrane A, Li can be recovered even when using nanofiltration membrane D, which has a large difference in magnesium sulfate removal rate and magnesium chloride removal rate, but due to Ca... 2+ High permeability, Li + The permeability of Li is reduced, therefore Li + / Ca 2+ It is lower than that of Example 9.

[0227] [Comparative Example 1]

[0228] Except for changing the treated water c to treated water e and dilution water II to dilution water VI, the same method as in Example 1 was used. The analytical results of the permeate composition are shown in Table 5. When the pH value of the treated water is less than 10, Li... + Almost impermeable, Li + The recovery rate has decreased significantly.

[0229] [Comparative Example 2]

[0230] Except for converting the treated water c to treated water d, the same method as in Example 1 was used. The analysis results of the permeate composition are shown in Table 5. The OH content of the treated water... - Concentration ratio of Li + High concentration, therefore Ca 2+ It has high permeability, and the Li in the permeate is high. + / Ca 2+ Significantly reduced.

[0231] [Comparative Example 3]

[0232] Except for replacing nanofiltration membrane B with nanofiltration membrane C, the same method as in Example 1 was used. The analytical results of the permeate composition are shown in Table 5. Nanofiltration membrane C has a low MgSO4 removal rate and high Ca... 2+ It has high permeability, and the Li in the permeate is high. + / Ca 2+ Significantly reduced.

[0233]

[0234] As can be seen from the above results, compared with Comparative Examples 1 to 3, Examples 1 to 12, which are the methods for recovering alkali metal ions and hydroxide ions of the present invention, can recover lithium ions and hydroxide ions as alkali metal ions with high purity and high recovery rate.

[0235] Industry availability

[0236] By using the recycling method and recycling apparatus of the present invention, for example, an aqueous solution containing high purity of lithium ions and hydroxide ions can be obtained with a high lithium ion recovery rate, which is suitable for manufacturing lithium hydroxide required for the positive electrode precursor of high-nickel lithium-ion batteries, which have seen a surge in demand in recent years.

[0237] Although the invention has been described in detail with reference to specific aspects, it will be apparent to those skilled in the art that various changes and modifications can be made to the invention without departing from its spirit and scope.

[0238] Furthermore, this application is based on Japanese Patent Application No. 2023-169364, filed on September 29, 2023, which is incorporated herein by reference in its entirety.

[0239] Explanation of symbols in attached drawings

[0240] 1. Water to be treated

[0241] 2 original sinks

[0242] 3 nanofiltration membrane elements

[0243] 4. Through the liquid tank

[0244] 5. Ultrafiltration membrane

[0245] 6. Dilution water

[0246] 7 pumps

[0247] 8 Anion Exchange Resin

Claims

1. A method for recovering alkali metal ions and hydroxide ions from treated water, comprising a nanofiltration step of separating the treated water by a nanofiltration membrane. The water being treated contains alkali metal ions and polyvalent ions, has a pH above 10, and its hydroxide ion concentration is lower than the sum of the alkali metal ion concentrations. All ion concentrations are expressed in mol / L. The difference between the glucose removal rate when the nanofiltration membrane permeates a 1000 mg / L glucose aqueous solution at 25°C and pH 6.5 under an operating pressure of 0.5 MPa and the isopropanol removal rate when it permeates a 1000 mg / L isopropanol aqueous solution at 25°C and pH 6.5 under an operating pressure of 0.5 MPa is greater than 40%, the glucose removal rate is greater than 70%, and the magnesium sulfate removal rate when it permeates a 2000 mg / L magnesium sulfate aqueous solution at 25°C and pH 6.5 under an operating pressure of 0.5 MPa is greater than 95%.

2. The recovery method according to claim 1, wherein the total concentration of alkali metal ions other than sodium and potassium ions in the treated water is more than 1 times the concentration of chloride ions, and the total concentration of alkali metal ions other than sodium and potassium ions is more than 1 times the total concentration of sodium ions and potassium ions, wherein the unit of ion concentration is mol / L.

3. The recovery method as described in claim 1 or 2 further comprises a circulation step of mixing the concentrate obtained from the nanofiltration step with the water to be treated, and a step of controlling the water to be treated at a pH of 10 or higher.

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

5. The recovery method according to claim 4, wherein the hydroxide of the polyvalent cation is calcium hydroxide.

6. The recovery method of claim 3 further comprises 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 with a pH of 10 or higher.

7. The recovery method of claim 3 further includes the step of permeating the concentrate through an ultrafiltration membrane.

8. The recycling method of claim 3 further comprises the steps of contacting at least one of the treated water and the concentrate with anion exchange resin and mixing with the treated water.

9. The recovery method according to claim 1 or 2, wherein the difference between the magnesium sulfate removal rate of the nanofiltration membrane and the magnesium chloride removal rate when a 2000 mg / L magnesium chloride aqueous solution at 25°C and pH 6.5 is permeated under an operating pressure of 0.5 MPa is less than 20%, and the glucose removal rate is more than 70% and less than 90%.

10. The recovery method according to claim 1 or 2, wherein the alkali metal ion comprises at least one selected from lithium ions, rubidium ions, cesium ions and francium ions.

11. An alkali metal hydroxide, which is recovered from a solution containing alkali metal ions and hydroxide ions obtained by the recovery method according to claim 1 or 2.

12. A positive electrode material for a lithium-ion battery, which is synthesized using the alkali metal hydroxide of claim 11, wherein the alkali metal hydroxide is lithium hydroxide.

13. A recovery device for recovering alkali metal ions and hydroxide ions from treated water, comprising a nanofiltration unit for separating the treated water by a nanofiltration membrane. The water being treated contains alkali metal ions and polyvalent ions, has a pH above 10, and has a hydroxide ion concentration lower than the sum of the alkali metal ion concentrations. All ion concentrations are expressed in mol / L. The difference between the glucose removal rate when the nanofiltration membrane permeates a 1000 mg / L glucose aqueous solution at 25°C and pH 6.5 under an operating pressure of 0.5 MPa and the isopropanol removal rate when it permeates a 1000 mg / L isopropanol aqueous solution at 25°C and pH 6.5 under an operating pressure of 0.5 MPa is greater than 40%, the glucose removal rate is greater than 70%, and the magnesium sulfate removal rate when it permeates a 2000 mg / L magnesium sulfate aqueous solution at 25°C and pH 6.5 under an operating pressure of 0.5 MPa is greater than 95%.

14. The recovery apparatus of claim 13, further comprising a circulation unit for mixing the concentrate obtained through the nanofiltration unit with the water to be treated, and a unit for permeating the concentrate through an ultrafiltration membrane.

15. The recovery apparatus of claim 13 or 14, further comprising a unit for contacting at least one of the treated water and the concentrate obtained through the nanofiltration unit with anion exchange resin and mixing it with the treated water.

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