Method for producing organic compound-containing polymer particles and method for separating and purifying rare earth elements

Abstract

To provide a method for producing organic compound-containing polymer particles capable of economically and efficiently manufacturing organic compound-containing polymer particles, and a rare earth element separation and purification method capable of efficiently extracting metal ions in an aqueous solution, especially heavy rare earth elements represented by dysprosium, and performing separation and purification thereof.SOLUTION: In a method for producing polymer particles containing an organic compound, aqueous suspension polymerization is carried out by using a vinyl monomer containing a polyvinyl monomer, in the presence of an organic compound capable of extracting metal ions, with a water-soluble polymer as a suspension stabilizer, and, in producing polymer particles containing the organic compound, the water-soluble polymer is crosslinked. Furthermore, the organic compound-containing polymer particles produced by the method are used for separation and purification of rare earth elements.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing organic compound-containing polymer particles and a method for separating and purifying rare earth elements. [Background technology]

[0002] Rare earth elements have a wide range of applications, including permanent magnets, laser materials, catalysts, and phosphors. Neodymium (Nd) among light rare earth elements and dysprosium (Dy) among heavy rare earth elements are particularly important for electric vehicle motors, where demand has increased significantly in recent years. However, their supply structure is unevenly distributed across production areas. Dysprosium, in particular, is mostly supplied from China, and its vulnerability has been pointed out. Furthermore, environmental destruction during the extraction and refining processes of these rare earth elements is also a problem, and there is a demand for production methods that take into consideration reduction of the environmental burden, including recycling.

[0003] Known methods for separating and purifying a target rare earth element from an aqueous solution of rare earth elements include a solvent extraction method using an extractant (Patent Document 1) and a precipitation method using alkali, oxalic acid, or the like (Patent Document 2). Separation and purification by adsorption methods using adsorbents are also being investigated. Adsorbents that have been investigated include those with functional groups that have specific adsorption properties for various rare earth elements (Patent Documents 3 and 4), adsorbents in which a hydrophobic substrate is impregnated with an extractant (Patent Document 5), and synthetic adsorbents that are impregnated with an extractant and then coated with polyvinyl alcohol (Non-Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-184503 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-249674 [Patent Document 3] Japanese Patent Application Publication No. 2019-77906 [Patent Document 4] International Publication No. 2020 / 225964 [Patent Document 5] Japanese Patent Application Publication No. 4-80336 [Non-patent literature]

[0005] [Non-Patent Document 1] Environmental Technology,Vol.34,p1307(2013). [Non-patent document 2] Separation and Purification Technology,Vol.192,p62(2018). Summary of the Invention [Problem to be solved by the invention]

[0006] Due to its physical properties, the extractant used in solvent extraction is distributed in water at a fixed ratio. This results in losses of the extractant distributed in the water and the rare earth elements extracted with it during each extraction process, and there are also problems with the long mixing and settling process. Furthermore, when an adsorbent impregnated with an extractant is used, a certain amount of extractant will leak from the adsorbent, although the long mixing and standing process required in solvent extraction is not required. To prevent this, coating the surface of the adsorbent impregnated with the extractant requires a step of coating the surface of the adsorbent in addition to the step of impregnating the substrate with the extractant. This increases the number of steps and complicates the process, resulting in problems in terms of productivity and manufacturing costs. On the other hand, in the case of adsorbents into which functional groups with specific adsorption properties for various rare earth elements have been introduced, although the functional groups do not distribute in water, the manufacturing cost of the functional groups with specific adsorption properties is high, the introduction rate of the functional groups into the substrate constituting the polymer particles is low, and the chemical durability of the introduced functional groups is unclear, making it difficult to say that they are sufficient from an economic standpoint.

[0007] The present invention has been made in view of the above problems, and an object of the present invention is to provide organic compound-containing polymer particles useful as adsorbents capable of efficiently separating and purifying heavy rare earth elements such as dysprosium, with fewer production steps and at low production costs. Another object of the present invention is to provide a method for efficiently extracting target substances using the organic compound-containing polymer particles, in particular a method for efficiently separating and purifying heavy rare earth elements such as dysprosium. [Means for solving the problem]

[0008] As a result of extensive research, the present inventors have discovered a method for producing organic compound-containing polymer particles, which comprises aqueous suspension polymerizing a vinyl monomer containing a polyvinyl monomer as a constituent component in the presence of an organic compound capable of extracting metal ions, and crosslinking a water-soluble polymer used as a suspension stabilizer when producing polymer particles containing the organic compound, and have also discovered that the organic compound-containing polymer particles obtained by this production method can efficiently separate and purify heavy rare earth elements, typified by dysprosium, and have thus completed the present invention.

[0009] That is, the gist of the present invention is as follows. [1] In the production of polymer particles containing a vinyl monomer including a polyvinyl monomer by aqueous suspension polymerization in the presence of an organic compound capable of extracting metal ions, using a water-soluble polymer as a suspension stabilizer, A method for producing organic compound-containing polymer particles, which comprises crosslinking the water-soluble polymer. [2] The method for producing organic compound-containing polymer particles according to [1], wherein the organic compound capable of extracting metal ions is mono-2-ethylhexyl (2-ethylhexyl)phosphonate. [3] The method for producing organic compound-containing polymer particles according to [1] or [2], wherein the water-soluble polymer is a cellulose-based water-soluble polymer. [4] The method for producing organic compound-containing polymer particles according to any one of [1] to [3], wherein the polyvinyl monomer contains an aromatic polyvinyl monomer. [5] The method for producing organic compound-containing polymer particles according to any one of [1] to [4], wherein the vinyl monomer includes an aromatic vinyl monomer. [6] A method for producing organic compound-containing polymer particles according to any one of [1] to [5], comprising forming at least one of an imino group and an acetal group using an aldehyde as a method for crosslinking the water-soluble polymer. [7] A method for separating and purifying rare earth elements, which uses organic compound-containing polymer particles obtained by the production method according to any one of [1] to [6]. [Effects of the Invention]

[0010] According to the production method of the present invention, organic compound-containing polymer particles can be produced economically and efficiently. Furthermore, the method for separating and purifying rare earth elements of the present invention can efficiently extract, separate, and purify metal ions, particularly heavy rare earth elements such as dysprosium, from an aqueous solution. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 10 is a graph showing the amount of dysprosium adsorption determined after various shaking times when 20 mg of the polymer particles obtained in Example 1 was added to 10 mL of a 1 mmol / L aqueous dysprosium solution adjusted to pH 3.5 in Example 2. [Figure 2] FIG. 1 shows the amount of dysprosium adsorption determined after various shaking times when 20 mg of the metal extractant-impregnated polymer particles obtained in Comparative Example 1 was added to 10 mL of a 1 mmol / L dysprosium aqueous solution adjusted to pH 3.5 in Comparative Example 2. [Figure 3] In Example 3, 10 mL of an aqueous solution having a dysprosium concentration and a neodymium concentration of 1 mmol / L was added to 10 mL of a pH adjusting solution consisting of an HNO3 or NaOH aqueous solution and 20 mg of the polymer particles obtained in Example 1, and the mixture was shaken for a predetermined period of time, and the adsorption amounts of dysprosium and neodymium at each pH were determined. [Figure 4]This figure shows the adsorption amounts of dysprosium and neodymium at each pH level determined in Comparative Example 3 after adding 10 mL of a pH-adjusting solution made of an HNO3 or NaOH aqueous solution and 20 mg of the metal extractant-impregnated polymer particles obtained in Comparative Example 1 to 10 mL of an aqueous solution with a dysprosium concentration and a neodymium concentration of 1 mmol / L each, and shaking for a predetermined period of time. [Figure 5] In Example 4, 1.95 mL of the polymer particles obtained in Example 1 was placed in a glass column having an inner diameter of 10 mm and a length of 10 cm, and an aqueous solution having a dysprosium concentration of approximately 1 mmol / L and a neodymium concentration of approximately 5 mmol / L each and a pH of approximately 1.45 was passed through the column in an upward flow manner at a flow rate of 0.24 mL / min (adsorption step (a)).The aqueous solution was then switched to deionized water to push out the dysprosium / neodymium mixed system inside the column, and then a 2 mol / L aqueous HCl solution was passed through the column (desorption step (b)).This shows the dysprosium and neodymium concentrations in the adsorption step (a) and desorption step (b). [Figure 6] In Example 5, 1.95 mL of the polymer particles obtained in Example 1 was placed in a glass column having an inner diameter of 10 mm and a length of 10 cm, and an aqueous solution having a dysprosium concentration of approximately 1 mmol / L and a neodymium concentration of approximately 5 mmol / L each and a pH of approximately 1.45 was passed through the column in an upward flow at a flow rate of 0.24 mL / min in an amount of 88.6 times the volume of the polymer particles. Subsequently, an aqueous solution having a dysprosium concentration of approximately 0.055 mmol / L and a pH of approximately 1.45 was passed through the column in an amount of 73.8 times the volume of the polymer particles (adsorption / scrubbing step (a)). Subsequently, the aqueous dysprosium solution in the column was pushed out by switching to deionized water, and then a 2 mol / L aqueous HCl solution was passed through the column (desorption step (b)). This shows the dysprosium and neodymium concentrations in the adsorption / scrubbing step (a) and the desorption step (b). DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be practiced with various modifications within the scope of the gist. In this specification, when the expression "to" is used, it is intended to include the numerical values ​​or physical property values ​​before and after it. In this specification, "(meth)acrylic" refers to "acrylic," "methacrylic," or both, and "(meth)acrylate" refers to "acrylate," "methacrylate," or both. "Polyvinyl monomer" refers to a monomer having multiple vinyl groups in one molecule, and "monovinyl monomer" refers to a monomer having only one vinyl group in one molecule.

[0013] [Method of manufacturing organic compound-containing polymer particles] The method for producing organic compound-containing polymer particles of the present invention is a method in which a vinyl monomer including a polyvinyl monomer is subjected to aqueous suspension polymerization using a water-soluble polymer as a suspension stabilizer in the presence of an organic compound capable of extracting metal ions, and the water-soluble polymer is crosslinked when producing the organic compound-containing polymer particles. The organic compound-containing polymer particles produced by the production method of the present invention are polymer particles that contain, in their porous structure, an organic compound capable of extracting metal ions.

[0014] [Organic compounds] The organic compound capable of extracting metal ions in the present invention is an organic compound that is not freely miscible with water in a liquid state, in order to enable aqueous suspension polymerization, and examples thereof include organic compounds classified as water-insoluble liquids in Class 4 of the Fire Service Act.

[0015] Examples of organic compounds capable of extracting metal ions include amines such as tri-n-octylamine, Aliquat 336 (trioctylmethylammonium chloride), and Adogen 464 (methyltrialkyl(C8-C10)ammonium chloride); amides such as 2,2'-(methylimino)bis(N,N-di-n-octylacetamide) and N,N-dioctylbutanamide; and phosphate compounds such as dibutyl N,N-diethylcarbamoylmethylphosphonate, dihexyl N,N-diethylcarbamoylmethylphosphonate, tributyl phosphate, trioctyl phosphate, dioctyl phosphate, and PC-88A (mono-2-ethylhexyl (2-ethylhexyl)phosphonate). Among these, PC-88A: mono-2-ethylhexyl (2-ethylhexyl)phosphonate is preferred because it can efficiently extract, separate and purify heavy rare earth elements such as dysprosium.

[0016] [Polymer particles] The polymer constituting the polymer particles produced in the present invention is a polymer having structural units derived from vinyl monomers, including polyvinyl monomers. The vinyl monomers used for the polymer particles may include monovinyl monomers in addition to polyvinyl monomers. Examples of polymers constituting the polymer particles produced in the present invention include acrylic resins, styrene resins, triallyl isocyanurate resins, and vinyl ether resins. Among these, acrylic resins and styrene resins are preferred because of their excellent mechanical strength. Furthermore, when extracting, separating, and purifying heavy rare earth elements such as dysprosium, the pH of the aqueous solution must be low, so styrene resins, which have excellent hydrolysis resistance, are more preferred.

[0017] In this specification, "acrylic resin" refers to a resin in which (meth)acrylate-derived structural units account for 50% by mass or more of 100% by mass of all vinyl monomer-derived structural units constituting the acrylic resin, and this proportion is preferably 80% by mass or more. The acrylic resin may also contain structural units derived from vinyl monomers other than (meth)acrylate.

[0018] Examples of (meth)acrylates as monovinyl monomers include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, stearyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate; hydroxyl group-containing (meth)acrylates such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and glycerin mono(meth)acrylate; epoxy group-containing (meth)acrylates such as glycidyl (meth)acrylate, 4,5-epoxybutyl (meth)acrylate, and 9,10-epoxystearyl (meth)acrylate; (meth)acrylamides such as (meth)acrylamide, dimethyl (meth)acrylamide, and hydroxyethyl (meth)acrylamide; and (meth)acrylonitrile. These may be used alone or in combination of two or more.

[0019] Examples of (meth)acrylates as polyvinyl monomers include alkylene di(meth)acrylates such as ethylene glycol di(meth)acrylate; polyalkylene glycol di(meth)acrylates such as polyethylene glycol di(meth)acrylate; glycerol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and N,N'-alkylenebis(meth)acrylamide. These may be used alone or in combination of two or more.

[0020] The content of the structural unit derived from the polyvinyl monomer in the acrylic resin is preferably 5 to 100% by mass, and more preferably 10 to 100% by mass, based on 100% by mass of the acrylic resin, from the viewpoint of mechanical strength. That is, when producing polymer particles of the acrylic resin, the content of the polyvinyl monomer in the vinyl monomer used is preferably 5 to 100% by mass, and more preferably 10 to 100% by mass, based on 100% by mass of the vinyl monomer, from the viewpoint of mechanical strength.

[0021] In this specification, "styrene-based resin" refers to a resin in which structural units derived from aromatic vinyl monomers account for 50% by mass or more of 100% by mass of all structural units derived from vinyl monomers constituting the styrene-based resin, and this proportion is preferably 80% by mass or more. The styrene-based resin may contain structural units derived from vinyl monomers other than aromatic vinyl monomers. In the present invention, the vinyl monomer preferably contains an aromatic vinyl monomer, and more preferably contains an aromatic polyvinyl monomer, that is, an aromatic vinyl monomer as a polyvinyl monomer.

[0022] Examples of aromatic vinyl monomers as monovinyl monomers include styrene, methylstyrene, ethylstyrene, α-methylstyrene, chlorostyrene, chloromethylstyrene, and bromobutylstyrene. These may be used alone or in combination of two or more. As the aromatic vinyl monomer as the monovinyl monomer, styrene is preferred from the viewpoint of industrial availability.

[0023] Examples of aromatic vinyl monomers as polyvinyl monomers include divinylbenzene, bis(vinylphenyl)ethane, divinylnaphthalene, and 2,4,6-trivinylethylbenzene. These may be used alone or in combination of two or more. As the aromatic vinyl monomer for the polyvinyl monomer, divinylbenzene is preferred from the viewpoint of industrial availability.

[0024] The content of the structural unit derived from the polyvinyl monomer in the styrene-based resin is preferably 2 to 100% by mass, and more preferably 4 to 100% by mass, based on 100% by mass of the styrene-based resin, from the viewpoint of mechanical strength. That is, when producing polymer particles of the styrene-based resin, the content of the polyvinyl monomer in the vinyl monomer used is preferably 2 to 100% by mass, and more preferably 4 to 100% by mass, based on 100% by mass of the vinyl monomer, from the viewpoint of mechanical strength.

[0025] In this specification, the term "triallyl isocyanurate resin" refers to a resin synthesized using triallyl isocyanurate as a crosslinking agent, and refers to a resin in which triallyl isocyanurate-derived structural units account for 10% by mass or more of 100% by mass of all vinyl monomer-derived structural units constituting the triallyl isocyanurate resin, and this proportion is preferably 20% by mass or more. The triallyl isocyanurate resin may contain structural units derived from vinyl monomers other than triallyl isocyanurate.

[0026] In this specification, "vinyl ether resin" refers to a resin in which, out of 100% by mass of all vinyl monomer-derived structural units constituting the vinyl ether resin, vinyl ether-derived structural units account for 50% by mass or more, and this proportion is preferably 80% by mass or more. The vinyl ether resin may also contain structural units of vinyl monomers other than vinyl ether.

[0027] Examples of vinyl ethers as monovinyl monomers include methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether, hydroxyethyl vinyl ether, and chloroethyl vinyl ether. These may be used alone or in combination of two or more.

[0028] Examples of vinyl ethers as polyvinyl monomers include ethylene glycol divinyl ether, diethylene glycol divinyl ether, and triethylene glycol divinyl ether. These may be used alone or in combination of two or more.

[0029] The content of the structural unit derived from the polyvinyl monomer in the vinyl ether resin is preferably 5 to 100% by mass, and more preferably 10 to 100% by mass, based on 100% by mass of the vinyl ether resin, from the viewpoint of mechanical strength. That is, when producing polymer particles of the vinyl ether resin, the content of the polyvinyl monomer in the vinyl monomer used is preferably 5 to 100% by mass, and more preferably 10 to 100% by mass, based on 100% by mass of the vinyl monomer, from the viewpoint of mechanical strength.

[0030] [Aqueous suspension polymerization] In the present invention, vinyl monomers including polyvinyl monomers are subjected to aqueous suspension polymerization in the presence of an organic compound capable of extracting metal ions, using a water-soluble polymer as a suspension stabilizer.

[0031] Aqueous suspension polymerization is a method in which an organic phase containing a vinyl monomer, a polymerization initiator, a porosifying agent, etc. is dispersed in an aqueous phase containing a suspension stabilizer, etc., and a polymerization reaction is carried out by heating, etc. When carrying out this aqueous suspension polymerization, an organic compound capable of extracting metal ions is used as a porosifying agent, thereby forming a state in which the porous structure of the produced polymer particles is impregnated with the organic compound capable of extracting metal ions.

[0032] [Polymerization initiator] Examples of the polymerization initiator include peroxide-based polymerization initiators such as di-t-hexyl peroxide, dicumyl peroxide, di-t-butyl peroxide, t-hexyl perbenzoate, t-hexylperoxyisopropyl carbonate, t-butylcumyl peroxide, diisopropylbenzene hydroperoxide, benzoyl peroxide, di-(3-methylbenzoyl) peroxide, benzoyl(3-methylbenzoyl) peroxide, di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate, di-2-ethoxyethyl peroxydicarbonate, di-sec-butyl peroxydicarbonate, t-hexyl peroxypivalate, t-butyl peroxybenzoate, hydrogen peroxide, and persulfates; and azo-based polymerization initiators such as azobisisobutyronitrile and 2,2'-azobis(2,4-dimethylvaleronitrile). These may be used alone or in combination of two or more. Among these, peroxide-based polymerization initiators are preferred because of their ease of handling and economic efficiency, and benzoyl peroxide, di-(3-methylbenzoyl) peroxide, benzoyl(3-methylbenzoyl) peroxide, and t-butyl peroxybenzoate are more preferred.

[0033] The amount of the polymerization initiator used may be appropriately determined depending on the type of vinyl monomer and polymerization initiator used, but is preferably 0.05 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, relative to 100 parts by mass of the total amount of vinyl monomers. When the amount of the polymerization initiator used is equal to or greater than the above lower limit, polymerization easily proceeds.

[0034] [Suspension stabilizer] Examples of water-soluble polymers used as suspension stabilizers include gelatin, starch, polyvinyl alcohol, partial hydrolyzed polyvinyl acetate, polyacrylamide, poly(dimethyldiallyl)ammonium chloride, carboxymethyl-methylcellulose, ethyl cellulose, methyl cellulose, hydroxypropyl methylcellulose, hydroxyethyl methylcellulose, and magnesium silicate. These may be used alone or in combination of two or more.

[0035] In the production method of the present invention, when a vinyl monomer containing a polyvinyl monomer as a constituent component is subjected to aqueous suspension polymerization in the presence of an organic compound capable of extracting metal ions, a water-soluble polymer used as a suspension stabilizer is crosslinked. Therefore, the suspension stabilizer needs to be a water-soluble polymer having functional groups capable of introducing a crosslinked structure. From this viewpoint, preferred water-soluble polymers used as suspension stabilizers are gelatin having amino groups; polyvinyl alcohol having hydroxyl groups, partial hydrolyzed polyvinyl acetate; and water-soluble cellulose polymers such as carboxymethyl-methylcellulose, ethyl cellulose, methyl cellulose, hydroxypropyl methylcellulose, and hydroxyethyl methylcellulose. Among these, cellulose-based water-soluble polymers are more preferred because they have excellent hydrolysis resistance and have the property of adhering to the surface of organic compound-containing polymer particles due to a decrease in water solubility near the polymerization reaction temperature, and methylcellulose, hydroxypropylmethylcellulose, and hydroxyethylmethylcellulose are even more preferred.

[0036] The content of the suspension stabilizer in the aqueous phase may be appropriately set depending on the type of aqueous phase components and the desired particle size, but is preferably 0.01 to 5 mass% and more preferably 0.05 to 3 mass% relative to the total amount of the aqueous phase (100 mass%). When the content of the suspension stabilizer is equal to or greater than the lower limit, coalescence and breakage of droplets in the organic phase are suppressed, resulting in excellent particle size uniformity of the droplets in the organic phase. Furthermore, when the content of the suspension stabilizer is equal to or less than the upper limit, it is preferable from the viewpoint of production costs.

[0037] In aqueous suspension polymerization, an organic phase and an aqueous phase are fed into a reactor, and the monomers are polymerized while the organic phase and the aqueous phase are kept in a suspended state by stirring or other means. The bath ratio of the organic phase to the aqueous phase, in terms of the volume of the organic phase:the volume of the aqueous phase, is preferably 1:0.5-15, and more preferably 1:1.5-10, in order to achieve excellent production reproducibility.

[0038] The polymerization temperature is preferably 20 to 250° C., more preferably 40 to 150° C. If the polymerization temperature is equal to or higher than the lower limit, the polymerization proceeds easily. On the other hand, if the polymerization temperature is equal to or lower than the upper limit, depolymerization can be suppressed.

[0039] The polymerization time is preferably 1 to 24 hours, more preferably 2 to 12 hours. When the polymerization time is equal to or more than the above lower limit, the polymerization easily proceeds. On the other hand, when the polymerization time is equal to or less than the above upper limit, the productivity of the resin is excellent.

[0040] The polymerization atmosphere may be air or an inert gas, but an inert gas is preferred because it is superior in safety and reproducibility of production. Examples of inert gases include nitrogen, carbon dioxide, and argon.

[0041] [Crosslinking agent and crosslinking method] In the present invention, in order to crosslink the water-soluble polymer used as a suspension stabilizer, it is preferable to use an aldehyde such as formaldehyde as a crosslinking agent. By using aldehydes as crosslinking agents, reactions with amino groups and hydroxyl groups present in the water-soluble polymer used as a suspension stabilizer proceed, resulting in imino or acetalization, thereby forming a crosslinked structure of at least one of imino groups and acetal groups. Specific examples of such crosslinking methods are described in Non-Patent Documents 1 and 2.

[0042] The shape of the organic compound-containing polymer particles of the present invention may be spherical or amorphous, but spherical is preferred because it can suppress pressure loss when the organic compound-containing polymer particles are packed into a column and passed through, increase the liquid passing rate, and provide excellent productivity in separating and purifying rare earth elements.

[0043] [Physical properties of polymer particles containing organic compounds] The volume average particle diameter of the organic compound-containing polymer particles produced by the production method of the present invention is preferably 1 to 1000 μm, more preferably 4 to 700 μm, and even more preferably 10 to 500 μm. When the volume average particle diameter of the organic compound-containing polymer particles is equal to or greater than the above lower limit, pressure loss when the organic compound-containing polymer particles are packed into a column and passed through can be suppressed, the liquid passage rate can be increased, and productivity during rare earth element separation and purification can be excellent. Furthermore, when the volume average particle diameter of the organic compound-containing polymer particles is equal to or less than the above upper limit, column efficiency, adsorption capacity, and separation performance can be excellent. In this specification, the volume average particle size of the organic compound-containing polymer particles is determined by measuring the particle sizes of 100 randomly selected polymer particles using an optical microscope, and calculating the volume median size from the distribution of the particle sizes.

[0044] The volume average particle diameter of the organic compound-containing polymer particles produced by the production method of the present invention can be adjusted by setting the polymerization conditions of the aqueous suspension polymerization, specifically, the type and amount of the vinyl monomer, the type and amount of the suspension stabilizer, the stirring rotation speed, etc. After the polymerization is completed, the polymer particles may be classified by a method such as a sieve, a water sieve, or an air sieve to make the volume average particle diameter of the polymer particles uniform.

[0045] The uniformity coefficient of the organic compound-containing polymer particles produced by the production method of the present invention is preferably 2.0 or less, more preferably 1.0 to 2.0, and even more preferably 1.0 to 1.6, because this can suppress pressure loss when the polymer particles are packed into a column and a liquid is passed through it. In this specification, the uniformity coefficient of organic compound-containing polymer particles is an index of the particle size distribution width, and is defined as the value obtained by dividing the particle size of the largest 40% of the particle sizes in the volume distribution of the polymer particles by the particle size of the largest 90% of the particle sizes.

[0046] The organic compound-containing polymer particles of the present invention are porous because they are prepared by aqueous suspension polymerization of vinyl monomers, including polyvinyl monomers, in the presence of an organic compound capable of extracting metal ions.

[0047] The specific surface area of ​​the organic compound-containing polymer particles produced by the production method of the present invention is 1 to 1000 m 2 / g is preferred, and 10 to 800m 2 / g is more preferable. When the specific surface area of ​​the organic compound-containing polymer particles is equal to or greater than the above lower limit, the content of the organic compound capable of extracting metal ions in the polymer particles is excellent. On the other hand, when the specific surface area of ​​the organic compound-containing polymer particles is equal to or less than the above upper limit, the diffusion and penetration of the rare earth element into the pores of the polymer particles is less likely to be hindered, resulting in excellent adsorption properties. In this specification, the specific surface area of ​​organic compound-containing polymer particles is measured by nitrogen gas adsorption (BET) method after removing the organic compound capable of extracting metal ions by solvent extraction and drying under reduced pressure. Specifically, the monolayer adsorption amount is calculated by the BET equation from the pressure change before and after nitrogen gas adsorption, and the specific surface area of ​​the polymer particles is calculated from the cross-sectional area of ​​one nitrogen gas molecule, according to ISO 9277. The specific surface area of ​​the organic compound-containing polymer particles can be adjusted by setting the polymerization conditions for aqueous suspension polymerization.

[0048] The pore diameter of the organic compound-containing polymer particles produced by the production method of the present invention is preferably 1 to 1000 nm, more preferably 2 to 500 nm, and even more preferably 3 to 200 nm. When the pore diameter of the organic compound-containing polymer particles is equal to or greater than the above lower limit, the contact frequency of the rare earth element with the polymer particle surface is excellent. When the pore diameter of the organic compound-containing polymer particles is equal to or less than the above upper limit, the polymer particles have excellent mechanical strength. In this specification, the pore diameter of organic compound-containing polymer particles is the most frequent diameter measured by mercury intrusion porosimetry if the most frequent diameter is 100 nm or greater after solvent extraction to remove organic compounds capable of extracting metal ions, followed by drying under reduced pressure. Alternatively, the most frequent diameter is measured by nitrogen gas adsorption if the most frequent diameter is less than 100 nm. Specifically, in the case of mercury intrusion porosimetry, pressure is applied to the polymer particles to cause mercury to penetrate the pores. Using the pressure value and the corresponding volume of invaded mercury, assuming the pores are cylindrical, the pore diameter is calculated using the Washburn equation, and ISO 15901-1 is applied mutatis mutandis. In the case of nitrogen gas adsorption, ISO 15901-2 is applied mutatis mutandis. The pore diameter of the organic compound-containing polymer particles can be adjusted by setting the polymerization conditions for aqueous suspension polymerization.

[0049] The pore volume of the organic compound-containing polymer particles produced by the production method of the present invention is preferably 0.01 to 3.0 mL / g, more preferably 0.1 to 2.5 mL / g, and even more preferably 0.2 to 2.0 mL / g. When the pore volume of the organic compound-containing polymer particles is equal to or greater than the above lower limit, the adsorption ability of rare earth elements is excellent. When the pore volume of the organic compound-containing polymer particles is equal to or less than the above upper limit, the mechanical strength of the polymer particles is excellent. In this specification, the pore volume of organic compound-containing polymer particles is the most frequent volume measured by mercury intrusion porosimetry if the most frequent diameter is 100 nm or more, or by nitrogen gas adsorption if the most frequent diameter is less than 100 nm, after removing organic compounds capable of extracting metal ions by solvent extraction and drying under reduced pressure. The pore volume of the organic compound-containing polymer particles can be adjusted by setting the polymerization conditions for aqueous suspension polymerization.

[0050] [Rare earth element separation and purification method] The method for separating and purifying rare earth elements of the present invention is a method for extracting, separating, and purifying rare earth elements present in an aqueous solution using organic compound-containing polymer particles produced by the production method of the present invention.

[0051] Examples of the method for separating and purifying rare earth elements of the present invention include a batch processing method in which an aqueous solution containing rare earth elements and organic compound-containing polymer particles are mixed and contacted in a container, and a column processing method in which an aqueous solution containing rare earth elements is passed through a column packed with organic compound-containing polymer particles. Among these methods for separating and purifying rare earth elements, the column treatment method is preferred because it allows rare earth elements to be efficiently extracted into the polymer particles and then separated and purified. In addition, in order to increase the purity of the target rare earth element adsorbed on the polymer particles during the column treatment, it is also preferable to add a scrubbing step in which an aqueous solution of the target rare earth element is passed through the polymer particles to push out untarget rare earth elements from the polymer particles.

[0052] [Application] The organic compound-containing polymer particles produced by the production method of the present invention are highly valuable in practical applications in the industrial field because they can efficiently separate and purify rare earth elements, particularly heavy rare earth elements such as dysprosium, from aqueous solutions. [Example]

[0053] The present invention will be explained in more detail below using examples, but the present invention is not limited to the description of the following examples as long as it does not deviate from the gist of the invention.

[0054] (1) Volume average particle size The volume average particle diameter of the obtained polymer particles was calculated by measuring the particle diameters of 100 randomly selected polymer particles using an optical microscope (model name "SMZ1500", manufactured by Nikon Corporation) and calculating the volume median diameter from the distribution.

[0055] (2) Uniformity coefficient The uniformity coefficient of the obtained polymer particles was calculated by measuring the particle diameters of 100 randomly selected polymer particles using an optical microscope (model name "SMZ1500", manufactured by Nikon Corporation), and dividing the particle diameter that is 40% of the largest particle diameters on a volume basis by the particle diameter that is 90% of the largest particle diameters.

[0056] (3) Specific surface area Organic compounds capable of extracting metal ions were removed from the obtained polymer particles by solvent extraction, and the particles were dried. After that, they were weighed and their specific surface area was measured by the nitrogen gas adsorption method (BET method) using a specific surface area measuring device (model name "Flowsorb", manufactured by Micromeritics).

[0057] (4) Pore diameter and pore volume Organic compounds capable of extracting metal ions were removed from the obtained polymer particles by solvent extraction, and the particles were dried under reduced pressure. Thereafter, the pore diameter and pore volume were measured by the mercury intrusion method using an automatic porosimeter (model name "Autopore 9520", manufactured by Micromeritics) or the nitrogen gas adsorption method using a pore distribution analyzer (model name "ASAP2400", manufactured by Micromeritics).

[0058] [Reference example 1] <Production of polymer particles containing uncrosslinked water-soluble polymers used as suspension stabilizers> A mixture consisting of 30 parts by weight of industrial divinylbenzene (Nippon Steel Chemical & Material Co., Ltd., DVB-570, divinylbenzene purity: approximately 57%), 42 parts by weight of PC-88A (2-ethylhexyl) mono-2-ethylhexyl phosphonate, and 0.40 parts by weight of benzoyl peroxide (purity: approximately 75%, remainder: water) was added to an aqueous solution consisting of 0.36 parts by weight of partially saponified polyvinyl alcohol and 210 parts by weight of deionized water, and the mixture was stirred to form a suspension. The suspension was heated to 80°C under a nitrogen atmosphere and polymerized for 6 hours. After cooling, the resulting particles were washed with water to obtain polymer particles. Mono-2-ethylhexyl (2-ethylhexyl)phosphonate was extracted with acetone and dried under reduced pressure to give polymer particles with a specific surface area of ​​401 m 2The physical properties were: pore diameter 56.6 nm, pore volume 0.82 mL / g.

[0059] [Example 1] <Production of polymer particles> A mixture consisting of 30 parts by weight of industrial divinylbenzene (DVB-570, divinylbenzene purity: approximately 57%, manufactured by Nippon Steel Chemical & Material Co., Ltd.), 30 parts by weight of PC-88A (2-ethylhexyl) mono-2-ethylhexyl phosphonate, and 0.40 parts by weight of benzoyl peroxide (purity: approximately 75%, remainder: water) was added to an aqueous solution consisting of 0.30 parts by weight of hydroxypropyl methylcellulose (Metolose 65SH-50, manufactured by Shin-Etsu Chemical Co., Ltd.) and 181 parts by weight of deionized water, and stirred to form a suspension. The suspension was heated to 80°C under a nitrogen atmosphere and polymerized for 6 hours. Two hours after the temperature was raised to 80°C, an aqueous solution consisting of 2.91 parts by weight of 98% sulfuric acid, 10.9 parts by weight of 25% aqueous glutaraldehyde solution, and 40 parts by weight of deionized water was added to crosslink the hydroxypropyl methylcellulose attached to the surface of the suspended polymer particles. After the polymerization reaction was completed, the mixture was cooled and the resulting particles were washed with water to obtain polymer particles. The obtained polymer particles had a volume average particle size of 371 μm and a uniformity coefficient of 1.3. The content of PC-88A in the obtained polymer particles was 1.86 mmol / g.

[0060] [Comparative Example 1] <Production of polymer particles impregnated with metal extractant> According to Non-Patent Documents 1 and 2, polymer particles HP2MG (manufactured by Mitsubishi Chemical Corporation) were impregnated with the metal extractant PC-88A: mono-2-ethylhexyl (2-ethylhexyl)phosphonate, and then coated with polyvinyl alcohol and crosslinked with glutaraldehyde to obtain metal extractant-impregnated polymer particles. The content of PC-88A in the resulting metal extractant-impregnated polymer particles was 2.06 mmol / g.

[0061] [Example 2] <Dysprosium adsorption measurement> DyCl3·6H2O was dissolved in deionized water, and 20 mg of the polymer particles obtained in Example 1 was added to 10 mL of a 1 mmol / L dysprosium aqueous solution adjusted to pH 3.5 with an aqueous HCl or NaOH solution. The mixture was stirred by orbital shaking at a temperature of 25°C and a rotation speed of 100 rpm. After a predetermined time (t (h)), the dysprosium concentration was quantified by ICP-AES using an ICPE-9000 (Shimadzu Corporation). The adsorption amount: q t The amount of dysprosium adsorbed at each shaking time is shown in Figure 1. When a 1 mmol / L dysprosium aqueous solution with a pH of approximately 1 was used, the leakage rate of PC-88A (mono-2-ethylhexyl (2-ethylhexyl)phosphonate) into the aqueous solution was 0.3%.

[0062] Comparative Example 2 <Dysprosium adsorption measurement> DyCl3·6H2O was dissolved in deionized water, and 20 mg of the metal extractant-impregnated polymer particles obtained in Comparative Example 1 was added to 10 mL of a 1 mmol / L dysprosium aqueous solution adjusted to pH 3.5 with an HCl or NaOH aqueous solution. The mixture was stirred by orbital shaking at a temperature of 25°C and a rotation speed of 100 rpm. After a predetermined time (t (h)), the dysprosium concentration was quantified by ICP-AES using an ICPE-9000 (Shimadzu Corporation). The adsorption amount: q t The amount of dysprosium adsorbed at each shaking time is shown in Figure 2. The equilibrium adsorption amount was about 0.3 mmol / g, as in Example 1, but the speed at which the equilibrium adsorption amount was reached was somewhat slow. When a 1 mmol / L dysprosium aqueous solution with a pH of approximately 1 was used, the leakage rate of PC-88A (mono-2-ethylhexyl (2-ethylhexyl)phosphonate) into the aqueous solution was 1.8%.

[0063] [Example 3] <Measurement of pH dependence of adsorption amount in dysprosium / neodymium mixed system> To 10 mL of an aqueous solution containing dysprosium and neodymium at 1 mmol / L each, 10 mL of a pH-adjusting solution consisting of an HNO3 or NaOH aqueous solution was added, and 20 mg of the polymer particles obtained in Example 1 was added. After stirring by orbital shaking at a temperature of 25°C and a rotation speed of 150 rpm for 24 hours or more, the dysprosium concentration was quantified by ICP-AES using an ICPE-9000 (Shimadzu Corporation), and the adsorption amounts q of dysprosium and neodymium at various pH values ​​were determined. The adsorption amounts of dysprosium and neodymium at each pH value are shown in Figure 3. As can be seen from FIG. 3, differences in the adsorption amounts of dysprosium and neodymium are observed in the pH range of 1 to 3, demonstrating the selectivity of the polymer particles obtained in Example 1 for dysprosium.

[0064] Comparative Example 3 <Measurement of pH dependence of adsorption amount in dysprosium / neodymium mixed system> To 10 mL of aqueous solutions with dysprosium and neodymium concentrations of 1 mmol / L each, 10 mL of a pH-adjusting solution consisting of HNO3 or NaOH solution was added, and 20 mg of chelating resin CR11 (Mitsubishi Chemical Corporation) with iminodiacetic acid functional groups was added. After orbital shaking at 25°C and 150 rpm for at least 24 hours, the dysprosium concentration was quantified by ICP-AES using a Shimadzu ICPE-9000, and the adsorption amounts (q) of dysprosium and neodymium at various pH levels were calculated. The adsorption amounts of dysprosium and neodymium at each pH level are shown in Figure 4. As shown in Figure 4, the adsorption behavior of dysprosium and neodymium is almost identical in the measured pH range, indicating that the chelating resin with iminodiacetic acid functional groups has no selectivity.

[0065] [Example 4] <Column adsorption / desorption measurement of dysprosium / neodymium mixed system> 1.95 mL of the polymer particles obtained in Example 1 was placed in a glass column with an inner diameter of 10 mm and a length of 10 cm, and an aqueous solution with a dysprosium concentration of approximately 1 mmol / L, a neodymium concentration of approximately 5 mmol / L each, and a pH of approximately 1.45 was passed through it in an upward flow at a flow rate of 0.24 mL / min using a Flom KP-21 pump. The dysprosium and neodymium concentrations at the column outlet were measured, and after saturated adsorption was confirmed, the water was switched to deionized water to push out the dysprosium / neodymium mixed aqueous solution from the column. Next, the dysprosium and neodymium adsorbed on the polymer particles were desorbed by passing a 2 mol / L aqueous HCl solution through the solution. Figure 5 shows the dysprosium and neodymium concentrations in the adsorption step (a) and desorption step (b). It is clear that dysprosium is selectively adsorbed onto the polymer particles, and that high-purity purification is possible in the desorption step using a 2 mol / L aqueous HCl solution. The purity of dysprosium in the desorbed solution was 97.1%.

[0066] [Example 5] <Column adsorption / desorption measurement of dysprosium / neodymium mixed system> 1.95 mL of the polymer particles obtained in Example 1 was placed in a glass column with an inner diameter of 10 mm and a length of 10 cm, and an aqueous solution with a dysprosium concentration of approximately 1 mmol / L, a neodymium concentration of approximately 5 mmol / L each, and a pH of approximately 1.45 was passed through it in an upward flow at a flow rate of 0.24 mL / min using a Flom KP-21 pump. After passing a dysprosium / neodymium mixed aqueous solution in an amount 88.6 times the volume of the polymer particles, a scrubbing step was carried out in which an aqueous solution with a dysprosium concentration of approximately 0.055 mmol / L and a pH of approximately 1.45 was passed in an amount 73.8 times the volume of the polymer particles, and then the solution was switched to deionized water to push out the dysprosium aqueous solution from the column. The dysprosium and neodymium adsorbed on the polymer particles were then desorbed by passing a 2 mol / L aqueous HCl solution through the solution. Figure 6 shows the dysprosium and neodymium concentrations in the adsorption and scrubbing process (a) and the desorption process (b). It is clear that dysprosium is selectively adsorbed onto the polymer particles, and that high-purity purification is possible in the desorption process using a 2 mol / L aqueous HCl solution. The purity of dysprosium in the desorbed solution was 99.4%.

[0067] As is clear from the above results, the method for producing organic compound-containing polymer particles of the present invention is capable of adsorbing heavy rare earth elements, typified by dysprosium, to an extent equal to or greater than that of metal extractant-impregnated polymer particles produced by existing technologies, and can produce organic compound-containing polymer particles with fewer production steps that exhibit lower leakage of the organic compound, which is the metal extractant and can extract metal ions, into an aqueous solution than that of metal extractant-impregnated polymer particles produced by existing technologies. Furthermore, the organic compound-containing polymer particles produced by the present invention have the ability to separate heavy rare earth elements such as dysprosium from light rare earth elements such as neodymium. [Industrial Applicability]

[0068] The method for producing organic compound-containing polymer particles of the present invention makes it possible to produce organic compound-containing polymer particles at low cost with a small number of steps. Furthermore, the organic compound-containing polymer particles of the present invention can be used to efficiently extract target substances. In particular, heavy rare earth elements such as dysprosium can be efficiently separated and purified on an industrial scale, making the particles extremely valuable in practical applications in the industrial field.

Claims

1. In the production of polymer particles containing a vinyl monomer including a polyvinyl monomer, the polymer is subjected to aqueous suspension polymerization in the presence of an organic compound capable of extracting metal ions, using a water-soluble polymer as a suspension stabilizer, A method for producing organic compound-containing polymer particles, which comprises crosslinking the water-soluble polymer.

2. 2. The method for producing organic compound-containing polymer particles according to claim 1, wherein the organic compound capable of extracting metal ions is mono-2-ethylhexyl (2-ethylhexyl)phosphonate.

3. 3. The method for producing organic compound-containing polymer particles according to claim 1, wherein the water-soluble polymer is a cellulose-based water-soluble polymer.

4. The method for producing organic compound-containing polymer particles according to claim 1 or 2, wherein the polyvinyl monomer comprises an aromatic polyvinyl monomer.

5. The method for producing organic compound-containing polymer particles according to claim 1 or 2, wherein the vinyl monomer comprises an aromatic vinyl monomer.

6. The method for producing organic compound-containing polymer particles according to claim 1 or 2, wherein the method for crosslinking the water-soluble polymer comprises forming at least one of an imino group and an acetal group using an aldehyde.

7. A method for separating and purifying rare earth elements, which uses organic compound-containing polymer particles obtained by the method according to any one of claims 1 to 6.

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