Sulfated yeast and method for producing same

Abstract

The purpose of the present invention is to provide a novel biological material with excellent metal adsorption properties.　A sulfated yeast containing a yeast and a sulfated polysaccharide on the surface of the yeast is useful as a novel biological material with excellent metal adsorption properties.

Description

Sulfating yeast and its manufacturing method

[0001] The present invention relates to a sulfurizing yeast and a method for producing the same.

[0002] The wastewater generated by mining activities or the processing of electronic waste contains residual heavy metals, which are then treated to separate them before being released into the environment. While chemical precipitation and ion exchange resin separation are commonly used, achieving separation to a level that meets stringent wastewater standards requires significant economic and environmental costs.

[0003] In recent years, metal removal methods using biological materials as adsorbents have been attracting attention. Microorganisms are particularly noteworthy as materials that can be obtained at low cost as by-products of the fermentation industry and are composed of uniform sizes and components, making them suitable materials for adsorbents. Non-Patent Document 1 reports the adsorption of metals using fungi, bacteria, algae, etc.

[0004] While such biological materials have low economic costs and low environmental impact, their performance is not sufficient. Aiming to improve the metal adsorption capacity of biological materials, research has been conducted on biomass immobilization, chemical modification of cell surfaces, and methods for expressing metal-binding proteins possessed by heavy metal-resistant bacteria on the cell surface using genetic engineering techniques. Non-Patent Document 2 reports that phosphorylated yeast with a phosphate content of approximately 1.0 mmol per gram of dry cell weight (DCW), obtained by treating baker's yeast with trisodium cyclotriphosphate hexahydrate, strongly adsorbs various metal ions due to its strong negative charge and can selectively recover rare earth ions such as neodymium. Furthermore, Patent Document 1 describes that cationized yeast with a surface zeta potential of 0 mV or higher, obtained by treating yeast with a cationizing agent, exhibits excellent selenium adsorption.

[0005] Ramrakhiani L. et al., Surface Modification of Naturally Available Biomass for Enhancement of Heavy Metal Removal Efficiency, Upscaling Prospects, and Manegement Aspects of Spent Biosorbents, Apply Biochemistryand Biotechnology, 180, 41-78 (2016)Yoshihiro Ojima, Shogo Kosako, Maya Kihara, Norikazu Miyoshi, Koichi Igarashi & Masayuki Azuma, Recovering metals from aqueous solutions by biosorption onto phosphorylated dry baker's yeast, Scientific Reports volume 9, Article number: 225 (2019)

[0006] Japanese Patent Application Laid-Open No. 2023-038686

[0007] An object of the present invention is to provide a new biomaterial with excellent metal adsorption properties.

[0008] The inventors were inspired by the excellent metal adsorption capacity of phosphorylating yeast and attempted to produce sulfating yeast. However, the efficiency of sulfate group modification in yeast was extremely low, and effective metal adsorption capacity could not be obtained. As a result of further intensive research, they found that the efficiency of sulfate group modification in yeast can be improved by selecting specific sulfation conditions, and that the sulfating yeast thus obtained has an unexpectedly high metal adsorption capacity. The present invention was completed through further research based on these findings.

[0009] That is, the present invention provides the following aspects. Item 1. A sulfating yeast comprising yeast and sulfated polysaccharides on the surface of the yeast. Item 2. The sulfating yeast according to Item 1, wherein the surface zeta potential is -24 mV or less. Item 3. The sulfating yeast according to Item 1 or 2, wherein the sulfur content per 1 g of dry cell weight is 1.2 mmol or more. Item 4. A metal adsorbent comprising the sulfating yeast according to any one of Items 1 to 3. Item 5. A selective adsorbent for rare earth elements comprising the sulfating yeast according to any one of Items 1 to 3. Item 6. A method for producing a sulfating yeast, comprising a sulfation step of treating a dry yeast with at least one sulfating agent selected from sulfur trioxide-pyridine complex and amidosulfuric acid. Item 7. The production method according to Item 6, wherein 0.4 mmol or more of the sulfating agent is used per 100 mg of the dry yeast. Item 8. The production method according to Item 6 or 7, wherein a base is co-present in the sulfation step. Item 9. Item 10. A method for adsorbing metal ions, comprising the step of contacting an aqueous solution containing metal ions to be adsorbed with the metal adsorbent according to Item 4, thereby adsorbing the metal ions. Item 11. A method for adsorbing metal ions, comprising the step of contacting an aqueous solution containing rare earth element ions to be adsorbed and metal element ions other than rare earth element ions, and having a hydrogen ion concentration of 0.06 M or more, with the selective adsorbent according to Item 5, thereby selectively adsorbing the rare earth element ions. Item 12. A method for producing water from which metal ions have been removed, comprising the steps of contacting an aqueous solution containing metal ions with the metal adsorbent according to Item 4, thereby adsorbing the metal ions onto the metal adsorbent, and removing the metal adsorbent to which the metal ions have been adsorbed. Item 6. A method for producing recycled rare earth elements, comprising: a step of contacting the selective adsorbent according to Item 5 with an aqueous solution containing rare earth element ions and ions of a metal element other than the rare earth element ions and having a hydrogen ion concentration of 0.06 M or more, thereby adsorbing the rare earth element ions onto the selective adsorbent; a step of recovering the selective adsorbent to which the rare earth element ions have been adsorbed; and a step of liberating the rare earth element ions from the recovered selective adsorbent.

[0010] According to the present invention, a new biological material with excellent metal adsorption properties is provided.

[0011] The zeta potential measurement results of the sulfurizing yeast obtained in Test Example 1 are shown. The FT-IR measurement results of the sulfurizing yeast obtained in Test Example 1 are shown. The elemental analysis results (amount of sulfur substance per 1 g of dry cell weight) of the sulfurizing yeast obtained in Test Example 1 are shown. The zeta potential measurement results of the sulfurizing yeast obtained in Test Example 2 are shown. The FT-IR measurement results of the sulfurizing yeast obtained in Test Example 2 are shown. The elemental analysis results (amount of sulfur substance per 1 g of dry cell weight) of the sulfurizing yeast obtained in Test Example 2 are shown. Cu by the sulfurizing yeast obtained in Test Examples 1 and 2 2+ The adsorption amount of Dy by the sulfuric acid-producing yeast obtained in Test Examples 1 and 2 is shown (Test Example 3). 3+ The adsorption amount of rare earth element ions (Dy) by the sulfurized yeast obtained in Test Example 1 is shown (Test Example 4). 3+ The relationship between the adsorption amount of various metal ions, including rare earth ions (Dy), and the hydrochloric acid concentration is shown in Test Example 5. 3+ 1 shows the relationship between the adsorption amount of various metal ions, including ions of HCl, and the concentration of hydrochloric acid (Test Example 5).

[0012] 1. Sulfating Yeast The sulfating yeast of the present invention is characterized by comprising yeast and sulfated polysaccharides on the surface of the yeast. The sulfating yeast of the present invention will be described in detail below. In this specification, a numerical range indicated by two numbers and a prefix "to" includes the two numbers as the lower and upper limits. For example, the expression "2 to 15% by weight" means 2% by weight or more and 15% by weight or less.

[0013] 1-1. Yeast The yeast that serves as the base for the sulfurizing yeast of the present invention is not particularly limited as long as it is a yeast classified into the Ascomycota or Basidiomycota.

[0014] Specific examples of yeasts classified into the Ascomycota include the genus Saccharomyces, such as Saccharomyces cerevisiae, Saccharomyces pastrianus, Saccharomyces bayanus, Saccharomyces carlsbergensis, Saccharomyces sake, Saccharomyces uvarum, Saccharomyces pastorianus (carlsbergenisis), Saccharomyces bayanus, and Saccharomyces awamori; Pichia pastoris, Pichia angusta, Pichia finlandica, and Pichia trehalophila. Pichia species such as Pichia trehalophila, Pichia koclamae, Pichia membranaefaciens, and Pichia minuta; Schizosaccharomyces species such as Schizosaccharomyces pombe; Dekkera species such as Dekkera bruxellensis and Dekkera anomala; Kluyveromyces lactis, Kluyveromyces marxianus, and Kluyveromyces Kluyveromyces such as Kluyveromyces fragilis; Aureobasidium such as Aureobasidium pullulans; Zygosacoharomyces such as Zygosacoharomyces rouxi;and yeasts belonging to the genus Candida, such as Candida utilis, Candida versatilis, and Candida etchellsii.

[0015] Specific examples of yeasts classified into the phylum Basidiomycota include yeasts belonging to the genus Sporobolomyces; and yeasts belonging to the genus Rhodotorula, such as Rhodotorula mucilaginosa.

[0016] The above yeasts may be used alone or in combination of two or more kinds. Among them, yeasts of the genus Saccharomyces are preferred, and Saccharomyces cerevisiae is more preferred.

[0017] 1-2. Sulfated Polysaccharides The sulfated polysaccharides in the sulfated yeast of the present invention are polysaccharides naturally present on the surface of yeast, to which sulfate groups have been introduced as modifying groups. The type of polysaccharide depends on the type of yeast used, but generally includes mannans such as α-mannan, glucans such as β-glucan, and chitin. The sulfate groups are introduced via ester bonds to hydroxyl groups of the polysaccharide.

[0018] Yeast is inherently negatively charged, but the sulfated polysaccharides of the present invention have a stronger negative charge due to the introduction of sulfate groups as modifying groups. The introduction rate of sulfate groups (modification rate) is not particularly limited and may vary depending on the level of inherent negative charge of the yeast. Examples of the zeta potential include, but are not limited to, -24 mV or less, preferably -25 mV or less, more preferably -28 mV or less, or -30 mV or less, even more preferably -32 mV or less, or -34 mV or less. The lower limit of the zeta potential is also not particularly limited, but examples include -50 mV or more. Specifically, examples of the zeta potential include -50 mV or more to -24 mV or less, preferably -50 mV or more to -25 mV or less, more preferably -50 mV or more to -28 mV or less, or -50 mV or more to -30 mV or less, even more preferably -50 mV or more to -32 mV or less, or -50 mV or more to -34 mV.

[0019] The zeta potential is measured by the following method: Sulfating yeast is suspended in water to a turbidity of 0.5 at 600 nm, and 750 μL of the resulting suspension is dispensed into a cell, and the Z-potential is measured by electrophoretic light scattering using, for example, a Zetasizer Nano ZS (manufactured by Malvern) at room temperature (25° C.) without stirring.

[0020] Furthermore, the introduction rate (modification rate) of sulfate groups is such that the sulfur content per 1 g of dry cell weight (dry weight of sulfated polysaccharide) is 1.2 mmol or more, preferably 2 mmol or more, more preferably 2.5 mmol or more, even more preferably 3.0 mmol or more, and even more preferably 3.5 mmol or more. The upper limit of the sulfur content per 1 g of dry cell weight is not particularly limited, but may be, for example, 5 mmol or less. Specifically, the sulfur content per 1 g of dry cell weight is 1.2 mmol to 5 mmol, preferably 2 mmol to 5 mmol, more preferably 2.5 mmol to 5 mmol, even more preferably 3.0 mmol to 5 mmol, and even more preferably 3.5 mmol to 5 mmol.

[0021] 1-3. Uses The sulfurizing yeast of the present invention can be used as a metal adsorbent (i.e., an adsorbent for metal ions). The metals to be adsorbed by the metal adsorbent are not particularly limited, but examples include heavy metals (metals with a specific gravity of 4 or more). Heavy metals include iron (Fe), lead (Pb), gold (Au), silver (Ag), copper (Cu), chromium (Cr), cadmium (Cd), mercury (Hg), zinc (Zn), arsenic (As), manganese (Mn), cobalt (Co), nickel (Ni), molybdenum (Mo), tungsten (W), tin (Sn), bismuth (Bi), uranium (U), plutonium (Pu), platinum group elements, and rare earth elements. Platinum group elements include ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt). Examples of rare earth elements include scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0022] The sulfurizing yeast of the present invention can also be used as a selective adsorbent for rare earth elements. Specific forms of the metal adsorbent or selective adsorbent for rare earth elements are described in "3. Metal adsorbent and selective adsorbent for rare earth elements," and specific methods using the metal adsorbent or selective adsorbent for rare earth elements are described in "4. Method for adsorbing metal ions," "5. Method for producing water from which metal ions have been removed," and "6. Method for producing recycled rare earth elements," which will be described later.

[0023] 2. Method for Producing Sulfating Yeast The method for producing sulfating yeast of the present invention is a method for producing the sulfating yeast described in "1. Sulfating Yeast" above, and is characterized by including a sulfation step in which dried yeast is treated with at least one sulfating agent selected from sulfur trioxide-pyridine complex (CHNSO) and amidosulfuric acid (MHSOH).

[0024] 2-1. Dried Yeast The type of yeast used as an ingredient is as described above in "1-1. Yeast." The yeast is used in the form of dried yeast. Dried yeast refers to yeast from which water has been removed. In the present invention, the dried yeast used is yeast that has been freeze-dried and then dried under reduced pressure in the presence of a desiccant. Examples of desiccant include diphosphorus pentoxide, calcium chloride, soda lime, silica gel, and molecular sieves, with diphosphorus pentoxide being preferred.

[0025] 2-2. Sulfating Agent As the sulfating agent, at least one of sulfur trioxide pyridine complex (CHNSO) and amidosulfuric acid (MHSOH) is used. Either one of these sulfating agents may be used alone, or both may be used in combination.

[0026] The amount of sulfating agent used is not particularly limited, and when the equivalent is the same amount (theoretical amount) as the number of hydroxyl groups on the yeast surface polysaccharide, examples include 0.8 equivalents or more, 1 equivalent or more, preferably 1.6 equivalents or more, more preferably 1.8 equivalents or more, and even more preferably 2 equivalents or more, 3.5 equivalents or more, 4 equivalents or more, 6 equivalents or more, 8 equivalents or more, 10 equivalents or more, or 12 equivalents or more. The upper limit of the amount of sulfating agent used is also not particularly limited, and examples include 20 equivalents or less, 19 equivalents or less, 16 equivalents or less, 15 equivalents or less, 13 equivalents or less, 11 equivalents or less, 9 equivalents or less, 7 equivalents or less, 5 equivalents or less, or 3 equivalents or less. Specific examples of the amount of sulfating agent used include, for example, 0.8 to 20 equivalents, 1 to 20 equivalents, preferably 1.6 to 19 equivalents, more preferably 1.8 to 19 equivalents, even more preferably 2 to 16 equivalents, 3.5 to 16 equivalents, 4 to 16 equivalents, 6 to 15 equivalents, 8 to 15 equivalents, 10 to 13 equivalents, or 12 to 13 equivalents; and also include 0.8 to 16 equivalents, 1 to 15 equivalents, preferably 1.6 to 13 equivalents, more preferably 1.8 to 11 equivalents, even more preferably 2 to 9 equivalents, 3.5 to 7 equivalents, or 3.5 to 5 equivalents.

[0027] The number of hydroxyl groups on the yeast surface polysaccharides can be appropriately determined based on common technical knowledge. For example, assuming that the yeast surface polysaccharides are entirely composed of glucose residues, the total amount of glucose residues can be set to 24% by weight of the dry yeast. Therefore, the theoretical amount can be calculated by multiplying the weight of the dry yeast material by 0.24, dividing by the molecular weight of glucose (180), and multiplying by the number of hydroxyl groups per glucose residue (3).

[0028] Specifically, the amount of sulfating agent used per 100 mg of dry yeast material is, for example, 0.4 mmol or more, preferably 0.64 mmol or more, more preferably 0.72 mmol or more, and even more preferably 0.8 mmol or more, 1.6 mmol or more, 2.4 mmol or more, 3.2 mmol or more, 4 mmol or more, or 4.8 mmol or more. The upper limit of the amount of sulfating agent used is not particularly limited, and examples thereof include, for example, 8 mmol or less, 7.6 mmol or less, 6.4 mmol or less, 6 mmol or less, 5.2 mmol or less, 4.4 mmol or less, 3.6 mmol or less, 2.8 mmol or less, 2 mmol or less, or 1.2 mmol or less per 100 mg of dry yeast material. Specific examples of the amount of sulfating agent used per 100 mg of the dry yeast material include, for example, 0.4 mmol to 8 mmol, preferably 0.64 mmol to 7.6 mmol, more preferably 0.72 mmol to 6.4 mmol, even more preferably 0.8 mmol to 6 mmol, 1.6 mmol to 5.2 mmol, 2.4 mmol to 5.2 mmol, 3.2 mmol to 5.2 mmol, 4 mmol to 5.2 mmol, 4.4 mmol to 5.2 mmol, or 4.8 mmol to 5.2 mmol; and also include 0.4 mmol to 5.2 mmol, 0.64 mmol to 4.4 mmol, more preferably 0.72 mmol to 3.6 mmol, even more preferably 0.8 mmol to 2.8 mmol, and even more preferably 1.3 mmol to 2 mmol.

[0029] 2-3. Base In the method for producing sulfating yeast of the present invention, it is preferable to use a base together with the sulfating agent. Examples of the base include, but are not limited to, pyridine (Py) and 4-dimethylaminopyridine (DMAP). These bases may be used alone or in combination.

[0030] When the base is liquid at room temperature, a dehydrated base is used. Examples of the dehydrated base include a dehydrated base (having a water content of 50 ppm or less).

[0031] The amount of base used is not particularly limited, and examples of the amount per 1000 mmol of sulfating agent include 0.9 mmol or more, 0.95 mmol or more, 5 mmol or more, 10 mmol or more, 50 mmol or more, 100 mmol or more, 300 mmol or more, or 500 mmol or more. The upper limit of the amount of base used is also not particularly limited, and examples of the amount per 1000 mmol of sulfating agent include 2000 mmol or less, 1000 mmol or less, 900 mmol or less, 800 mmol or less, 700 mmol or less, 600 mmol or less, 550 mmol or less, 400 mmol or less, 200 mmol or less, 60 mmol or less, 20 mmol or less, 7 mmol or less, or 2 mmol or less. Specific examples of the amount of base used per 1000 mmol of sulfating agent include, for example, 0.9 mmol to 2000 mmol, 0.95 mmol to 2000 mmol, 5 mmol to 1000 mmol, 10 mmol to 900 mmol, 50 mmol to 800 mmol, 100 mmol to 700 mmol, 300 mmol to 600 mmol, and 500 mmol to 550 mmol; also include 0.9 mmol to 1000 mmol, 0.9 mmol to 400 mmol, 0.9 mmol to 200 mmol, 0.9 mmol to 60 mmol, 0.9 mmol to 20 mmol, 0.9 mmol to 7 mmol, and 0.9 mmol to 2 mmol.

[0032] 2-4. Solvent The solvent used in the sulfation step is not particularly limited as long as it is an organic solvent. Examples of the organic solvent include dimethylformamide (DMF) and dimethylacetamide (DMA). These organic solvents may be used alone or in combination.

[0033] The organic solvent may be either a dehydrated solvent or a non-dehydrated solvent. Examples of the dehydrated solvent include a dehydrated solvent (water content of 50 ppm or less, preferably 30 ppm or less) and a super-dehydrated solvent (water content of 10 ppm or less).

[0034] 2-5. Reaction Conditions The temperature for the sulfation reaction is, for example, 65 to 80° C., preferably 68 to 77° C. The time for the sulfation reaction is, for example, 1.5 to 4 hours, preferably 2 to 3.5 hours.

[0035] 2-6. Other Steps The method for producing sulfating yeast of the present invention can include any other steps in addition to the sulfation step. Examples of other steps that follow the sulfation step include removal of liquid (e.g., solid-liquid separation such as centrifugation), washing with water and removal of liquid, and addition of a base and removal of liquid. The recovered sulfating yeast can be obtained in an appropriately dried state (e.g., freeze-drying).

[0036] 3. Metal adsorbent and selective adsorbent for rare earth elements The metal adsorbent and selective adsorbent for rare earth elements of the present invention include the sulfating yeast described above in "1. Sulfating yeast." The metal adsorbent and selective adsorbent for rare earth elements of the present invention may consist essentially of the sulfating yeast described above, or may contain other materials.

[0037] When the metal adsorbent and the selective adsorbent for rare earth elements of the present invention are essentially composed of sulfurizing yeast (i.e., when they are produced using only the above-mentioned sulfurizing yeast, or when they are produced by further chemically modifying the above-mentioned sulfurizing yeast), such adsorbents may be in the form of the above-mentioned sulfurizing yeast itself, or in the form of an aggregate of the sulfurizing yeast, or in the form of bacterial cells chemically crosslinked with a crosslinking agent.

[0038] When the metal adsorbent and the selective adsorbent for rare earth elements of the present invention contain other materials, the other materials are not particularly limited as long as they do not impair the adsorption of the target metal or the selective adsorption of the rare earth elements. Examples of other materials include a water-insoluble carrier for supporting the sulfurizing yeast. Examples of insoluble carriers include organic polymers, inorganic polymers, and composites thereof. Specific examples of sulfurizing yeast supported on a water-insoluble carrier include those in which the sulfurizing yeast is physically or ionically adsorbed or chemically bonded to the water-insoluble carrier; those in the form of beads in which the sulfurizing yeast is gelled together with an organic polymer; those in which the sulfurizing yeast is encapsulated in a porous capsule; and those in which the sulfurizing yeast is immobilized on a filter or other filtering material.

[0039] In the selective adsorbent for rare earth elements of the present invention, the above-mentioned various forms are appropriately selected so as to have resistance to acidic conditions where the hydrogen ion concentration is 0.06 M or more.

[0040] 4. Method for Adsorbing Metal Ions The method for adsorbing metal ions of the present invention is a method for adsorbing metal ions using the metal adsorbent or the selective adsorbent for rare earth elements described above in "3. Metal adsorbent and selective adsorbent for rare earth elements."

[0041] 4-1. Method for adsorbing metal ions using a metal adsorbent Specifically, the method for adsorbing metal ions of the present invention using the above-mentioned metal adsorbent includes a step of contacting the above-mentioned metal adsorbent with an aqueous solution containing metal ions to be adsorbed, thereby adsorbing the metal ions.

[0042] Details of the metal ions are as described above in "1-3. Uses." Specific examples of aqueous solutions containing metal ions include industrial wastewater and seawater.

[0043] Specific examples of the manner in which a metal adsorbent is brought into contact with an aqueous solution containing metal ions to be adsorbed include a manner in which the aqueous solution and the metal adsorbent are stirred and mixed, and a manner in which the metal adsorbent is used as the stationary phase and the aqueous solution is used as the mobile phase.

[0044] The temperature conditions for adsorbing metal ions include, for example, 15 to 45° C., preferably 20 to 40° C., and more preferably 25 to 35° C. The contact time between the aqueous solution containing metal ions and the metal adsorbent is, for example, 1 to 30 minutes, 3 to 20 minutes, 5 to 15 minutes, or 8 to 12 minutes.

[0045] 4-2. Method for adsorbing metal ions using a selective adsorbent The method for adsorbing metal ions of the present invention using the above-mentioned selective adsorbent for rare earth elements comprises the step of contacting the above-mentioned selective adsorbent with an aqueous solution containing rare earth element ions to be adsorbed and metal element ions other than rare earth element ions and having a hydrogen ion concentration of 0.06 M or more, thereby selectively adsorbing the rare earth element ions.

[0046] Specific examples of the manner in which the aqueous solution is brought into contact with the selective adsorbent include a manner in which the aqueous solution and the selective adsorbent are stirred and mixed, and a manner in which the selective adsorbent is used as the stationary phase and the aqueous solution is used as the mobile phase.

[0047] Details of the rare earth element ions and metal element ions other than rare earth element ions are as described above in "1-3. Uses." Specific examples of aqueous solutions containing these metal ions include industrial wastewater and seawater.

[0048] The hydrogen ion concentration is preferably 0.06 M or more, more preferably 0.08 M or more or 0.09 M or more. The upper limit of the hydrogen ion concentration is not particularly limited, and examples thereof include 0.4 M or less, 0.35 M or less, 0.3 M or less, 0.25 M or less, 0.2 M or less, 0.15 M or less, and 0.12 M or less. Specific examples of the hydrogen ion concentration include preferably 0.06 M or more and 0.4 M or less, 0.06 M or more and 0.35 M or less, and 0.06 M or more and 0.3 M or less, more preferably 0.08 M or more and 0.25 M or less, 0.08 M or more and 0.2 M or less, 0.09 M or more and 0.15 M or less, and 0.09 M or more and 0.12 M or less.

[0049] The liquid conditions for adsorbing rare earth element ions may be any environment having the above-mentioned hydrogen ion concentration. The temperature conditions for adsorbing rare earth element ions may be, for example, 15 to 45°C, preferably 20 to 40°C, and more preferably 25 to 35°C. The contact time between the aqueous solution containing metal ions and the metal adsorbent may be, for example, 1 to 30 minutes, 3 to 20 minutes, 5 to 15 minutes, or 8 to 12 minutes.

[0050] 5. Method for Producing Water from Which Metal Ions Have Been Removed The method for producing water from which metal ions have been removed of the present invention is a method for producing water from which metal ions have been removed using the metal adsorbent described above in "3. Metal adsorbent and selective adsorbent for rare earth elements."

[0051] Specifically, the method of the present invention for producing water from which metal ions have been removed includes a step of contacting an aqueous solution containing metal ions with the above-mentioned metal adsorbent to adsorb the metal ions onto the metal adsorbent (adsorption step), and a step of removing the metal adsorbent to which the metal ions have been adsorbed (removal step).

[0052] Details of the metal ions are as described above in "1-3. Uses." Specific examples of aqueous solutions containing metal ions are as described above in "4-1. Method for adsorbing metal ions using a metal adsorbent." Specific aspects of contacting the metal adsorbent in the adsorption step and adsorption conditions are as described above in "4-1. Method for adsorbing metal ions using a metal adsorbent."

[0053] The specific technique for the removal step can be appropriately determined depending on the specific manner in which the metal adsorbent is contacted in the adsorption step. For example, if the aqueous solution and the metal adsorbent are stirred and mixed in the adsorption step, the liquid may be recovered in the removal step using any solid-liquid separation method (e.g., precipitation, centrifugation, etc.). Furthermore, if the metal adsorbent is used as the stationary phase and the aqueous solution is used as the mobile phase in the adsorption step, the mobile phase may be separated by flowing it out of the stationary phase and then recovered in the removal step.

[0054] 6. Method for Producing Recycled Rare Earth Elements The method for producing recycled rare earth elements of the present invention is a method for producing recycled rare earth elements using the selective adsorbent for rare earth elements described above in "3. Metal adsorbent and selective adsorbent for rare earth elements."

[0055] Specifically, the method for producing recycled rare earth elements includes a step of contacting the selective adsorbent with an aqueous solution containing rare earth element ions and ions of a metal element other than the rare earth element ions and having a hydrogen ion concentration of 0.06 M or more, thereby adsorbing the rare earth element ions onto the selective adsorbent (adsorption step), a step of recovering the selective adsorbent to which the rare earth element ions have been adsorbed (recovery step), and a step of liberating the rare earth element ions from the recovered selective adsorbent (liberation step).

[0056] Details of the rare earth element ions and metal element ions other than rare earth element ions are as described above in "1-3. Uses." Specific examples of aqueous solutions containing these metal ions and details of the hydrogen ion concentrations are as described above in "4-2. Method for adsorbing metal ions using a selective adsorbent." Specific aspects of contacting the selective adsorbent in the adsorption step, liquid conditions, and adsorption conditions are as described above in "4-2. Method for adsorbing metal ions using a selective adsorbent."

[0057] The specific method of the recovery step can be appropriately determined depending on the specific mode of contacting the selective adsorbent in the adsorption step. For example, if the aqueous solution and the selective adsorbent are stirred and mixed in the adsorption step, the recovery step may involve recovering the solid using any solid-liquid separation method (e.g., precipitation, centrifugation, etc.). Furthermore, if the selective adsorbent is used as the stationary phase and the aqueous solution is used as the mobile phase in the adsorption step, the recovery step may involve separating the mobile phase from the stationary phase and recovering the stationary phase.

[0058] In the release step, the recovered solid is brought into contact with water adjusted to a pH higher than that of the adsorption step, thereby releasing the adsorbed rare earth elements. The rare earth elements released in the water (recycled rare earth elements) can be recovered by separating them from the selective adsorbent.

[0059] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0060] [Test Example 1] (1) Preparation of Sulfate Group-Modified Yeast Three grams of dry yeast (Nissin, Super Camellia, S. cerevisiae) was suspended in 50 mL of pure water and centrifuged at 3000 × g for 2 minutes to collect the cells. This series of operations was called the washing procedure, and the washing procedure was repeated five times. Next, the yeast was fixed in 30 mL of 70% ethanol for 2 hours. After that, the yeast was washed five times with 50 mL of pure water (3000 × g for 2 minutes), flash-frozen with liquid nitrogen, and then dried in a freeze dryer for 2 to 3 days. Next, the yeast was dried under reduced pressure in the presence of diphosphorus pentoxide to obtain dried yeast.

[0061] Dry yeast (0.08 g) was soaked in 1 mL of DMF (ultra-dehydrated) overnight and allowed to swell. The DMF was removed, and a solution of sulfur trioxide-pyridine complex (CHNSO) and dehydrated pyridine (in the amounts shown in Table 1) in DMF (ultra-dehydrated) (1 mL) was added. The sulfation treatment was carried out by stirring in a 75°C oil bath for 2 hours. After the sulfation treatment, the reaction solution was returned to room temperature and centrifuged at 3000 × g for 2 minutes to collect the bacteria. The solution was then washed twice with 10 mL of pure water (3000 × g for 2 minutes). Next, 3 mL of 0.1 M NaOH (pH 9) was added, shaken at 140 rpm for 10 minutes, and centrifuged at 3000 × g for 2 minutes to collect the bacteria. This procedure was repeated four times. Finally, the solution was washed four times with 10 mL of pure water (3000 × g for 2 minutes) and lyophilized.

[0062] (2) Zeta potential measurement of sulfurized yeast. Dry yeast before sulfation or sulfurized yeast was added to pure water at OD 600 The yeast was suspended so that the pH was 0.5. 750 μL of this suspension was dispensed into a cell (DTS1070 cell, manufactured by Malvern), and the Z-potential was measured using a Zetasizer Nano ZS (Malvern). The surface charge of the yeast can be evaluated by the zeta potential, and a lower zeta potential indicates a stronger negative charge. The results are shown in Table 1 and Figure 1.

[0063] (3) FT-IR measurement of sulfurized yeast Dry yeast before sulfation or sulfurized yeast was subjected to FT-IR (KBr method) measurement using FT / IR-4000 (JAS.CO). -1 The intensity of the absorption peak of the sulfate group (A) appearing in the vicinity of 1200 to 950 cm -1 The ratio (A / B) of the intensity of the absorption peak of a carbon-oxygen single bond (B) appearing near the peak was calculated. A larger A / B ratio indicates that more sulfate groups are bonded. The results are shown in Table 1 and Figure 2.

[0064] (4) Elemental Analysis 10 mg of the dried yeast before sulfation or the sulfated yeast was weighed, and the amount of sulfur was measured by vanadomolybdic acid colorimetry using a UV-1700 (Shimadzu Corporation), and the amount of sulfur per 1 g of dry cell weight (dry weight (dw)) (mmol / g dw) was calculated. The results are shown in Table 1 and FIG. 3.

[0065]

[0066] The results in Table 1 and Figure 1 showed a significant decrease in zeta potential, indicating that the sulfation yeast had a strong surface charge due to the sulfation treatment. The results in Table 1 and Figure 2 showed a significant increase in the A / B ratio, confirming sulfate group modification by the sulfation treatment. The results in Table 1 and Figure 3 showed that almost no sulfur was present in the yeast before sulfation (Comparative Example 1), whereas a significant amount of sulfur was present in the sulfation yeast (Example 1), confirming sulfate group modification by the sulfation treatment.

[0067] [Test Example 2] Sulfating yeast was prepared by the same procedure as in Test Example 1, except that the amount of dry yeast used, solvent, sulfating agent, base, and reaction conditions were changed as shown in Table 2.

[0068] The obtained sulfurizing yeast was subjected to zeta potential measurement (the results are shown in Table 2 and FIG. 4), IR measurement (the results are shown in Table 2 and FIG. 5), and elemental analysis (the results are shown in Table 2 and FIG. 6) in the same manner as in Test Example 1.

[0069]

[0070] The results in Table 2 and Figure 4 showed a significant decrease in zeta potential, indicating that the sulfation yeast had a strong surface charge due to the sulfation treatment. The results in Table 2 and Figure 5 showed a significant increase in the A / B ratio, confirming sulfate group modification by the sulfation treatment. The results in Table 2 and Figure 6 showed that almost no sulfur was present in the yeast before sulfation (Comparative Example 2), whereas a significant amount of sulfur was present in the sulfation yeast (Example 4), confirming sulfate group modification by the sulfation treatment.

[0071] When sulfurized yeast was produced using sulfur trioxide N,N-dimethylformamide complex (HCON(CH3)2.SO3) as the sulfating agent, the amount of sulfur per dry cell of the obtained sulfurized yeast was 0.41 mmol / g dw. Furthermore, the amount of phosphorus per dry cell of the phosphorylated yeast reported in Non-Patent Document 2 was approximately 1 mmol / g dw. Therefore, it was found that the sulfurized yeast obtained in Test Examples 1 and 2 had a high degree of surface modification.

[0072] [Test Example 3] Cu 2+ 2 mg of each of the yeasts of Comparative Examples 1 and 2 and the sulfuric acid yeasts of Examples 2 and 4 were added to 4 mL of an aqueous solution with a concentration of 100 ppm and suspended. These were shaken at 140 rpm at 30°C for 10 minutes to obtain Cu. 2+ After the adsorption, the mixture was centrifuged at 3000×g for 10 minutes. The supernatant was diluted 10-fold, and 50 μL of 1N HNO was added to make the solution acidic. This was used as a sample for ICP measurement.

[0073] Cu in ICP measurement sample 2+ The concentration was measured using Vista MPX Simultaneous ICP-OES (Varian Inc.), and the results indicated that the Cu adsorbed 2+ The adsorption rate (%) was obtained when the concentration was taken as 100%. The results are shown in Figure 7. Furthermore, the adsorption rate of Cu was calculated based on the following formula: 2+ The adsorption amount per dry weight of the cells was calculated.

[0074]

[0075] As shown in FIG. 7, both the sulfurizing yeasts of Examples 1 and 4 had high Cu content.2+ Furthermore, the adsorption amount was 1.62 mmol / g dw in Example 1 and 2.02 mmol / g dw in Example 4.

[0076] In addition, the Cu content of sulfurated yeast was determined by using sulfur trioxide N,N-dimethylformamide complex (HCON(CH3)2.SO3) as a sulfation agent. 2+ The adsorption amount was 0.20 mol / g dw, which is the same as that of Cu in phosphorylated yeast reported in Non-Patent Document 2. 2+ The adsorption amount was 1.08 mmol / g dw. Therefore, the sulfuric acid-modifying yeast obtained in Test Examples 1 and 2 did not adsorb Cu. 2+ The adsorption capacity was found to be high.

[0077] [Test Example 4] Dy 3+ 2 mg of each of the yeasts of Comparative Examples 1 and 2 and the sulfated yeasts of Examples 2 and 4 were added to 4 mL of an aqueous solution containing 100 ppm of Dy (a type of trivalent rare earth element) and suspended. The mixture was shaken at 140 rpm at 30°C for 10 minutes to obtain a suspension of Dy. 3+ After the adsorption, the mixture was centrifuged at 3000×g for 10 minutes. The supernatant was diluted 10-fold, and 50 μL of 1N HNO was added to make the solution acidic. This was used as a sample for ICP measurement.

[0078] Dy of ICP measurement sample 3+ The concentration was measured using Vista MPX Simultaneous ICP-OES (Varian Inc.), and the Dy concentration was calculated from the amount of Dy reduced from the solution before treatment. 3+ The adsorption rate was calculated. The results are shown in Figure 8. Furthermore, based on the above formula, 3+ The adsorption amount per dry weight of the cells was calculated.

[0079] As shown in FIG. 8, both the sulfurizing yeasts of Examples 1 and 4 had high Dy 3+ The adsorption rates are shown in Table 1. Furthermore, the adsorption amounts were 1.10 mmol / g dw in Example 1 and 1.22 mmol / g dw in Example 4. These adsorption amounts per weight were excellent and comparable to those of ion exchange resins.

[0080] [Test Example 5] K + , Cu 2+ , Zn 2+ , and Dy3+ A metal solution containing 10 ppm of each metal was prepared, with the hydrochloric acid concentration adjusted to 0.0001 M, 0.001 M, 0.01 M, 0.1 M, or 0.3 M. To this solution, 2 mg of the sulfurizing yeast from Example 1 or Example 4 was added, and the solution was shaken at 140 rpm for 10 minutes at 30°C to adsorb each metal. The solution was then centrifuged at 3000 x g for 10 minutes. 9 mL of the supernatant was used as the sample for ICP measurement.

[0081] The concentration of each metal in the ICP measurement sample was measured using a Vista MPX Simultaneous ICP-OES (Varian Inc.), and the adsorption rate of each metal was calculated from the amount of metal lost from the pre-treatment solution. The results are shown in Figures 9 and 10.

[0082] As shown in Figures 9 and 10, the sulfurizing yeasts of Examples 1 and 4 were particularly effective in reducing the amount of Dy, a rare earth element, when the hydrochloric acid concentration was 0.1M. 3+ was most selectively adsorbed.

Claims

1. A sulfated yeast comprising yeast and sulfated polysaccharides on the surface of the yeast.

2. The sulfurizing yeast according to claim 1, having a surface zeta potential of -24 mV or less.

3. The sulfur-producing yeast according to claim 1, having a sulfur content of 1.2 mmol or more per gram of dry cell weight.

4. A metal adsorbent comprising the sulfurizing yeast according to claim 1.

5. A selective adsorbent for rare earth elements comprising the sulfurizing yeast according to claim 1.

6. A method for producing a sulfated yeast, comprising a sulfation step of treating dry yeast with at least one sulfating agent selected from the group consisting of a sulfur trioxide pyridine complex and an amidosulfate.

7. The method according to claim 6, wherein the amount of the sulfating agent used is 0.4 mmol or more per 100 mg of the dry yeast.

8. The method according to claim 6, wherein a base is present in the sulfation step.

9. A method for adsorbing metal ions, comprising the step of contacting an aqueous solution containing the metal ions to be adsorbed with the metal adsorbent according to claim 4, thereby adsorbing the metal ions.

10. A method for adsorbing metal ions, comprising the step of contacting the selective adsorbent according to claim 5 with an aqueous solution containing rare earth element ions to be adsorbed and metal element ions other than rare earth element ions and having a hydrogen ion concentration of 0.06 M or more, thereby selectively adsorbing the rare earth element ions.

11. A method for producing water from which metal ions have been removed, comprising the steps of: contacting an aqueous solution containing metal ions with the metal adsorbent described in claim 4 to cause the metal ions to be adsorbed onto the metal adsorbent; and removing the metal adsorbent to which the metal ions have been adsorbed.

12. A method for producing recycled rare earth elements, comprising the steps of: contacting the selective adsorbent described in claim 5 with an aqueous solution containing rare earth element ions and ions of a metal element other than rare earth element ions and having a hydrogen ion concentration of 0.06 M or more, thereby allowing the rare earth element ions to be adsorbed onto the selective adsorbent; recovering the selective adsorbent to which the rare earth element ions have been adsorbed; and liberating the rare earth element ions from the recovered selective adsorbent.

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