Method for recovering rare earth elements

Abstract

The invention provides a rare earth element recovery method with low environmental load, which can realize rare earth element recovery at low cost and high efficiency. A method for recovering a rare earth element, the method comprising: an adsorption step for mixing a liquid containing rare earth element ions with saccharomyces cerevisiae to obtain a mixed liquid in which the rare earth element ions are adsorbed to the saccharomyces cerevisiae under acidity; a separation step for separating the torula yeast from the mixed solution obtained in the adsorption step; and a recovery step for recovering the rare earth element ions from the torulomyces cerevisiae separated in the separation step.

Description

Technical Field

[0001] The present invention relates to a method for recovering rare earth elements. Background Art

[0002] In recent years, as a method for recovering metals, a biosorption recovery method using biological materials such as microorganisms as adsorbents has been studied. By using inexpensive biological materials, it is expected as a method capable of recovering metals from low-grade minerals, factory wastewater, waste of electronic devices, etc. at low cost and with low environmental load.

[0003] Various techniques for recovering precious metals and rare earth elements (rare earth) by such a biosorption-based recovery method have been proposed.

[0004] For example, in Patent Document 1, a precious metal recovery method is disclosed, which includes: a step of bringing baker's yeast into contact with the precious metal ions in a liquid having a pH of 4 or less containing the precious metal ions; and a step of firing the yeast separated from the liquid. Specifically, as examples of the precious metal ions, recovery of gold ions, platinum ions, and palladium ions is described, and in addition, it is described that platinum ions can also be recovered from a liquid coexisting with chromium ions at pH 1.2.

[0005] In Patent Document 2, a gold recovery method is disclosed, which includes: a step of bringing baker's yeast into contact with a solution containing gold ions, iron ions, copper ions, and halide ions under acidic conditions; a step of performing solid-liquid separation; and a step of firing a mixture containing baker's yeast and gold. As the pH conditions of the solution, examples of pH < 0, pH 0.55, and pH 1.12 are described.

[0006] In Patent Document 3, a method for recovering rare earth elements is disclosed, which includes: a step of mixing a solution containing rare earth elements with fish milt and adsorbing the rare earth elements on the fish milt (the pH of the mixed solution is preferably 3 or more, more preferably around pH 4); a step of recovering the fish milt from the mixed solution; and a step of separating the rare earth elements from the recovered fish milt by adding an acidic solution. In addition, it is described that Nd and Dy can be selectively recovered from a solution coexisting with Fe.

[0007] In Patent Document 4, a method for selectively recovering precious metals or rare earth elements from a metal solution using a Cyanidium-derived substance or porphyrin is disclosed.

[0008] In Non-Patent Document 1, it is described that by phosphorylating baker's yeast, Cd 2+ , Cu 2+ , Pb 2+ , Zn2+ The adsorption amounts of heavy metal ions such as etc. In addition, it is described that phosphorylated baker's yeast can also adsorb Ce with high efficiency 3+ 、Dy 3+ 、Gd 3+ 、La 3+ 、Nd 3+ 、Y 3+ 、Yb 3+ and other rare earth element ions. It is also described that phosphorylated baker's yeast can selectively adsorb rare earth element ions (Nd 3+ and Yb 3+ ) from an aqueous solution containing heavy metal and rare earth element ions.

[0009] Patent Document 5 describes the following method: A liquid containing metal ions is mixed with baker's yeast, and the metal ions are adsorbed onto the baker's yeast under specific conditions, and the yeast after solid-liquid separation is treated to recover rare earth element ions and / or noble metal ions.

[0010] Prior art documents

[0011] Patent documents

[0012] Patent Document 1: Japanese Patent Laid-Open No. 2016-183371

[0013] Patent Document 2: Japanese Patent Laid-Open No. 2018-35413

[0014] Patent Document 3: Japanese Patent Laid-Open No. 2013-213272

[0015] Patent Document 4: International Publication No. 2017 / 111092

[0016] Patent Document 5: International Publication No. 2023 / 286850

[0017] Non-patent documents

[0018] Non-patent Document 1: Yoshihiro Ojima, et al., Recovering metals from aqueous solutions by biosorption onto phosphorylated dry baker's yeast, SCIENTIFIC REPORTS, Published online: 18, January 2019, www.nature.com / scientificreports Summary of the invention

[0019] Problems to be solved by the invention

[0020] In the conventional metal recovery methods that do not use biological materials, there are problems of high environmental burdens caused by CO2 emissions, sludge treatment, etc.

[0021] In addition, for the conventional metal recovery methods that use biological materials, further improvement in the recovery rate and / or selectivity is sought. In addition, the recovery methods described in Patent Documents 1 to 4 and Non-Patent Document 1 are batch-type and laboratory test-level recovery methods, and there is a problem of low productivity.

[0022] Furthermore, in the recovery method described in Patent Document 4, culturing is required when using a Cyanidium-derived substance, and in the recovery of rare earth elements, it is necessary to perform fermentation under quasi-anaerobic conditions with nitrogen gas introduced and in the dark under quasi-anaerobic heterotrophic conditions, and there is a problem of complicated operations.

[0023] In the recovery method described in Non-Patent Document 1, chemical modification of yeast as an adsorbent is required, and thus there is a problem of high cost for the adsorbent.

[0024] An object of the present invention is to solve the problems in view of the above circumstances, and to provide a rare earth element recovery method with low environmental burden that can achieve the recovery of rare earth elements at low cost and efficiently. Another object of the present invention is to provide a rare earth element recovery method with low environmental burden and high productivity suitable for industrialization.

[0025] Means for Solving the Problems

[0026] The present invention has the following aspects.

[0027] (1) A rare earth element recovery method, comprising:

[0028] An adsorption step of mixing a liquid containing rare earth element ions with Torulaspora, to obtain a mixed liquid in which the rare earth element ions are adsorbed to the Torulaspora under acidic conditions;

[0029] A separation step of separating the Torulaspora from the mixed liquid obtained in the adsorption step; and

[0030] A recovery step of recovering the rare earth element ions from the Torulaspora separated in the separation step.

[0031] (2) The rare earth element recovery method according to item 1, wherein

[0032] The pH of the mixed liquid in the adsorption step is 1.0 or more.

[0033] (3) The rare earth element recovery method according to item 1 or 2, wherein

[0034] The pH of the mixed solution in the adsorption process is 2.4 or less.

[0035] (4) The method for recovering rare earth elements according to any one of items 1 to 3, wherein

[0036] The method for recovering rare earth elements further includes: a leaching process, treating a solid containing rare earth elements with an acidic solution to leach rare earth element ions, obtaining an acidic liquid containing rare earth element ions,

[0037] Mixing the acidic liquid obtained in the leaching process with Torulaspora globosa to perform the adsorption process.

[0038] (5) The method for recovering rare earth elements according to item 4, wherein

[0039] The pH of the acidic solution used in the leaching process is 2.0 or less.

[0040] (6) The method for recovering rare earth elements according to item 4 or 5, wherein

[0041] The solid containing rare earth elements is a mineral containing rare earth elements.

[0042] (7) The method for recovering rare earth elements according to any one of items 4 to 6, wherein

[0043] The solid containing rare earth elements is apatite, iron hydroxide or manganese oxide containing rare earth elements.

[0044] (8) The method for recovering rare earth elements according to item 4 or 5, wherein

[0045] The solid containing rare earth elements is rare earth element mud.

[0046] (9) The method for recovering rare earth elements according to any one of items 1 to 8, wherein

[0047] The liquid before mixing with Torulaspora globosa further contains ions of metals other than rare earth elements.

[0048] (10) The method for recovering rare earth elements according to any one of items 4 to 8, wherein

[0049] The solid containing rare earth elements further contains metals other than rare earth elements,

[0050] The liquid before mixing with Torulaspora globosa further contains ions of metals other than rare earth elements.

[0051] (11) The method for recovering rare earth elements according to item 9 or 10, wherein

[0052] The metal other than rare earth elements is at least one selected from vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, magnesium, aluminum, calcium, and titanium.

[0053] (12) The method for recovering rare earth elements according to any one of items 4 to 8 and 10, wherein,

[0054] In the leaching step, the leaching time, which is the time for treatment with an acidic solution, is within 1 hour.

[0055] (13) The method for recovering rare earth elements according to any one of items 1 to 12, wherein,

[0056] The adsorption step is a step of continuously supplying the liquid and the Torulaspora globosa to a mixing tank and continuously extracting a mixed liquid containing the liquid and the Torulaspora globosa from the mixing tank.

[0057] (14) The method for recovering rare earth elements according to any one of items 1 to 13, wherein,

[0058] The separation step is a step of performing solid-liquid separation on the mixed liquid obtained in the adsorption step to obtain a separated solid component,

[0059] The recovery step is a step of performing acid treatment on the separated solid component obtained in the separation step to recover the rare earth element ions adsorbed on the Torulaspora globosa.

[0060] (15) The method for recovering rare earth elements according to any one of items 1 to 13, wherein,

[0061] The separation step is a step of performing solid-liquid separation on the mixed liquid obtained in the adsorption step to obtain a separated solid component,

[0062] The recovery step is a step of performing heat treatment on the separated solid component obtained in the separation step and burning the Torulaspora globosa to recover the rare earth element ions adsorbed on the Torulaspora globosa as its concentrate.

[0063] (16) The method for recovering rare earth elements according to item 15, wherein,

[0064] In the recovery step, the heat treatment of the separated solid component is performed by firing in an industrial furnace.

[0065] (17) The method for recovering rare earth elements according to item 15 or 16, wherein,

[0066] Powder is recovered from the exhaust gas of the heat treatment step, and the recovered powder is mixed with the separated solid component before the heat treatment step.

[0067] (18)The rare earth element recovery method according to any one of items 14 to 17, wherein,

[0068] The solid-liquid separation is performed by at least one selected from centrifugal separation, filtration, membrane separation, and sedimentation separation.

[0069] (19)The rare earth element recovery method according to any one of items 14 to 18, wherein,

[0070] The rare earth element recovery method further includes a drying step of reducing the moisture content of the separated solid component.

[0071] (20)The rare earth element recovery method according to any one of items 14 to 19, wherein,

[0072] The separated liquid component obtained by the solid-liquid separation in the separation step is mixed with the liquid containing rare earth element ions before mixing with the Torulaspora globosa.

[0073] Advantages of the Invention

[0074] According to an embodiment of the present invention, a rare earth element recovery method capable of recovering rare earth elements at low cost and high efficiency can be provided. In addition, according to other embodiments of the present invention, a rare earth element recovery method with high productivity suitable for industrialization can be provided. Furthermore, according to these embodiments, a rare earth element recovery method with a low environmental load can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 is a flowchart showing an example of the rare earth element recovery method according to an embodiment of the present invention.

[0076] Figure 2 is a flowchart showing another example of the rare earth element recovery method according to an embodiment of the present invention.

[0077] Figure 3 is a schematic diagram showing a structural example of an apparatus that can be used for the rare earth element recovery method according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0078] Hereinafter, preferred embodiments of the present invention will be described.

[0079] The rare earth element recovery method according to an embodiment of the present invention includes an adsorption step of mixing a liquid containing rare earth element ions with Torulaspora globosa to obtain a mixed solution in which rare earth element ions are adsorbed to the Torulaspora globosa under acidic conditions; a separation step of separating the Torulaspora globosa from the mixed solution obtained in the adsorption step; and a recovery step of recovering the rare earth element ions from the Torulaspora globosa separated in the separation step.

[0080] It should be noted that in the following description, the "liquid containing rare earth element ions" before mixing with yeast is also appropriately referred to as "metal dissolution liquid".

[0081] In the rare earth element recovery method according to an embodiment of the present invention, as a step of preparing a metal dissolution liquid (liquid containing rare earth element ions) to be mixed with Torula yeast, it may include a step (leaching step) of treating a solid substance containing rare earth elements with an acidic liquid to leach rare earth element ions to obtain an acidic liquid (leachate) containing rare earth element ions.

[0082] As the solid substance containing rare earth elements, there is no particular limitation as long as it is a solid or a substance containing rare earth elements, and it is preferably capable of leaching rare earth element ions by treatment with an acidic liquid. As such a solid substance, minerals such as apatite (calcium phosphate, etc.) containing rare earth elements, iron hydroxide, and manganese oxide are preferred, and rare earth element mud is particularly preferably used.

[0083] The rare earth element recovery method according to an embodiment of the present invention includes a step (adsorption step) of mixing a liquid containing rare earth element ions (metal dissolution liquid) with Torula yeast to adsorb rare earth element ions onto Torula yeast.

[0084] As the liquid containing rare earth element ions (metal dissolution liquid), the leachate obtained in the aforementioned leaching step can be preferably used.

[0085] Torula yeast (Torulayeast, scientific name: Candida utilis) that can be used in the embodiments of the present invention can be yeast widely used in food. It should be noted that the synonyms of Torula yeast are Cyberlindnera jadinii, Hansenula jadinii, Lindnera jadinii, Pichia jadinii, Saccharomyces jadinii, Torula utilis, Torulopsis utilis, Torulopsis utilis var. major.

[0086] Torula yeast is easily obtained and easy to handle, so the cost can be suppressed. In addition, in the embodiments of the present invention, since the adsorption rate of rare earth element ions to yeast is fast, the treatment efficiency of the metal dissolution liquid can be improved. In addition, thereby, the capacity of the mixing tank for mixing the metal dissolution liquid and Torula yeast can be reduced, and the recovery device used in the embodiments of the present invention can also be miniaturized.

[0087] In the embodiments of the present invention, the Torulaspora can be dead, and as long as the adsorption function of rare earth element ions is not hindered, dead bacteria such as waste yeast can be used. By using dead bacteria such as waste yeast, not only can the cost be reduced, but also the environmental load based on life cycle assessment (LCA) can be reduced. Furthermore, the activity of living yeast is affected by environmental factors (for example, when the external temperature is low, the activity of yeast stops), but since dead bacteria can be used, the influence of environmental factors is small.

[0088] The rare earth elements in the embodiments of the present invention are also called "rare earth elements", which are scandium (Sc), yttrium (Y), and lanthanide elements (15 elements from lanthanum (La) to lutetium (Lu) in the periodic table), that is, the rare earth elements are 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).

[0089] The liquid containing rare earth element ions (metal dissolution solution) in the embodiments of the present invention, that is, the liquid mixed with Torulaspora, is a liquid containing ions of at least one rare earth element selected from the above rare earth elements.

[0090] In the rare earth element recovery method of the embodiments of the present invention, the metal dissolution solution (the liquid mixed with Torulaspora) is not particularly limited as long as it contains ions of the rare earth element to be recovered, and a liquid containing ions of at least one rare earth element selected from 15 elements of Sc, Y, and lanthanide elements can be used. Specifically, a liquid containing ions of at least one rare earth element selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu can be used.

[0091] In addition, in the rare earth element recovery method of the embodiments of the present invention, the metal dissolution solution (the liquid mixed with Torulaspora) can contain heavy metal ions as ions of metals other than rare earth elements (metals not for recovery purposes). Examples of heavy metals include vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, etc., and at least one of them can be included. In addition, the metal dissolution solution in the embodiments of the present invention can contain at least one of ions of light metals such as magnesium, aluminum, calcium, and titanium.

[0092] In an embodiment of the present invention, the solvent of the metal dissolution solution (the liquid mixed with Torulaspora globosa) is preferably an aqueous solvent or an aqueous solvent containing water, and may also contain a water-soluble solvent other than water within a range that does not impair the adsorption of rare earth element ions by Torulaspora globosa. Examples of the water-soluble solvent include alcohols such as methanol, ethanol, and propanol, acetone, acetonitrile, dioxane, tetrahydrofuran, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and the like. The water content rate in the solvent is preferably 70 to 100% by volume, more preferably 80 to 100% by volume, still more preferably 90 to 100% by volume, and the solvent is particularly preferably water.

[0093] The metal dissolution solution (the liquid mixed with Torulaspora globosa) in an embodiment of the present invention can be prepared by treating a substance that extracts rare earth element ions (hereinafter, appropriately referred to as "object to be recovered").

[0094] The object to be recovered is not particularly limited as long as it is a substance that extracts rare earth element ions, and examples thereof include solids or liquids containing rare earth elements, rare earth element ions, or their salts. Examples of such an object to be recovered include solid substances containing rare earth elements such as apatite (calcium phosphate, etc.) containing rare earth elements, iron hydroxide, and manganese oxide. For example, mineral resources such as rare earth element mud and manganese nodules can be used.

[0095] As a treatment method for extracting rare earth element ions from the object to be recovered into the liquid, when the object to be recovered is a solid substance containing rare earth elements, it can be carried out by the aforementioned leaching process. For example, when the object to be recovered is a submarine mineral resource such as rare earth element mud, acid treatment is preferably carried out to obtain a leaching solution, and dilution or concentration treatment, solvent replacement, and pH adjustment can be carried out as needed to obtain a desired metal dissolution solution.

[0096] The acid treatment in the aforementioned leaching process preferably uses an acidic solution with a pH of 2.0 or less, and more preferably uses an acidic solution with a pH of 1.5 or less. Since the pH of the acidic solution is sufficiently low, rare earth element ions are easily dissolved and hydroxides are difficult to precipitate. The pH of the leaching solution (acidic solution containing rare earth element ions) obtained in the leaching process is also preferably 2.0 or less, and more preferably 1.5 or less. In addition, the pH of the acidic solution used in the acid treatment of the leaching process is preferably 1.0 or more, and the pH of the obtained leaching solution is also preferably 1.0 or more. By carrying out the acid treatment of the leaching process with an acidic solution having a pH of 1.0 or more, the difference in pH from the pH of the subsequent adsorption treatment (the pH of the mixed solution in the adsorption process) can be reduced. In this case, pH adjustment before the adsorption process can be omitted, or it can be carried out by fine adjustment.

[0097] For the acid treatment in the leaching process, acidic solutions of strong acids such as hydrochloric acid (aqueous HCl solution), sulfuric acid, and nitric acid can be preferably used. The concentration of the acid can be set, for example, in the range of 0.01 to 5 M (mol / L), or can be set in the range of 0.01 to 1 M (mol / L).

[0098] When the object to be recovered contains metals, their ions, or salts that are not the target of recovery, the liquid (leachate) obtained by treating the object to be recovered may contain ions of metals that are not the target of recovery.

[0099] The metal dissolution solution composed of the leachate obtained by treating the object to be recovered is preferably pre - removed of insoluble substances before mixing with yeast.

[0100] When using a solid substance mainly composed of apatite (such as calcium phosphate), such as rare - earth element mud, as the object to be recovered, the dissolution of rare - earth element ions based on acid treatment (leaching process) of the object to be recovered can be carried out rapidly. Therefore, the leaching time, that is, the time for treatment with the acidic solution in the leaching process, can be shortened, for example, it can be set within 1 hour. Thus, in addition to shortening the time required for the leaching process, when metal ions other than rare - earth element ions are difficult to dissolve into the acidic solution, the content of metal ions other than rare - earth element ions in the obtained metal dissolution solution can be reduced. For example, as shown in Table 2 described later, it can be seen that when the leaching time is 60 minutes or less, compared with the case of 24 hours, the content of Fe ions can be reduced.

[0101] In addition, the leaching of rare - earth elements proceeds rapidly with high yield regardless of temperature, but the leaching rate of heavy metals such as Fe contained in rare - earth element mud (outside the recovery target) increases with the increase in temperature. Therefore, from the viewpoints of energy conservation and metal selectivity, the temperature of the rare - earth element mud leaching process is preferably carried out at room temperature. The leaching process can be carried out in the range of, for example, 5 to 35 °C according to the ambient temperature, and is preferably carried out in the range of 10 to 30 °C.

[0102] The rare - earth element recovery method according to the embodiment of the present invention is a technique useful industrially as a method for recovering rare - earth elements from submarine mineral resources such as rare - earth element mud.

[0103] To adjust the pH, before mixing Torulaspora globosa with the metal dissolution solution, acids such as hydrochloric acid and sulfuric acid, or alkalis such as aqueous sodium hydroxide solution can be added as pH adjusters. In addition, after mixing the metal dissolution solution with Torulaspora globosa, to adjust the pH of the obtained mixed solution, acids such as hydrochloric acid and sulfuric acid, or alkalis such as aqueous sodium hydroxide solution can also be added as pH adjusters.

[0104] When the object to be recovered is treated under acidic conditions and the resulting leachate (metal dissolution solution) has the desired pH, pH adjustment can be omitted. Since the aforementioned leaching step is carried out under acidic conditions, pH adjustment of the resulting leachate (metal dissolution solution) can be omitted or only slightly adjusted, thus simplifying the process.

[0105] In the adsorption step of the embodiment of the present invention, the metal dissolution solution is mixed with Torulaspora globosa, and rare earth element ions are adsorbed onto Torulaspora globosa in the resulting mixed solution. The adsorption step can be carried out under atmospheric pressure conditions.

[0106] From the viewpoint of further improving the adsorption effect of rare earth element ions onto Torulaspora globosa, the adsorption step is preferably carried out under acidic conditions, and the pH of the mixed solution of the metal dissolution solution and Torulaspora globosa is preferably within a suitable pH range corresponding to the type of rare earth element to be recovered.

[0107] By the pH of the above-mentioned mixed solution in the adsorption step being within the pH range corresponding to the type of rare earth element to be recovered, the adsorption amount (recovery rate) and / or selectivity of rare earth element ions onto Torulaspora globosa can be increased. From such a viewpoint, the pH of the above-mentioned mixed solution in the adsorption step is preferably 0.1 or more, more preferably 0.5 or more, further preferably 0.8 or more, most preferably 1.0 or more. Additionally, it is preferably 3 or less, more preferably 2.4 or less, and further preferably 2.1 or less.

[0108] It should be noted that if the pH of the leachate in the leaching step and the mixed solution in the adsorption step is sufficiently low, even in the case of containing metal ions other than rare earth element ions (such as Fe ions, Al ions), and the metal ions are in a precipitated state, coprecipitation of rare earth element ions can be prevented.

[0109] The temperature of the mixed solution of the metal dissolution solution and Torulaspora globosa in the adsorption step can be set, for example, in the range of 1 to 40 °C. From the viewpoints of the energy cost of temperature management, the adsorption performance of Torulaspora globosa, and the stability of Torulaspora globosa and rare earth element ions in the liquid, it is preferably 10 °C or more, more preferably 15 °C or more, and further preferably 20 °C or more. On the other hand, as the upper limit of the temperature, it is preferably 35 °C or less.

[0110] The time for the adsorption of rare earth element ions onto Torulopsis glabrata in the adsorption process (hereinafter referred to as "adsorption time") is appropriately set according to the pH of the mixed solution, the content and type of rare earth element ions, and the content and type of other metal ions that are not the target for recovery, etc. For example, it can be set in the range of 5 to 60 minutes. From the perspective of allowing the rare earth element ions to be fully adsorbed onto Torulopsis glabrata, this adsorption time is preferably 10 minutes or more. On the other hand, from the perspective of efficiency, it is preferably 60 minutes or less, more preferably 40 minutes or less, and further preferably 30 minutes or less.

[0111] In addition, in this mixed solution, when other metal ions that are not the target for recovery and take time for adsorption onto yeast coexist with rare earth element ions that are the target for recovery and are adsorbed onto yeast in a relatively short time, by adjusting the adsorption time, the selectivity of the rare earth element ions that are the target for recovery can be improved.

[0112] In the adsorption process, the concentration of rare earth element ions that are the target for recovery in the metal dissolution solution or in the mixed solution of the metal dissolution solution and Torulopsis glabrata, and the concentration of this metal ion when other metal ions that are not the target for recovery are present can be appropriately adjusted according to the cell concentration of Torulopsis glabrata. For example, it can be appropriately set in the range of 1×10 －5 mol / m 3 ~1×10 4 mol / m 3 From the perspective of improving recovery efficiency, it is preferably 1×10 －1 mol / m 3 or more. From the perspective of recovery rate and / or selectivity, it is preferably 1×10 2 mol / m 3 or less.

[0113] In the adsorption process, the cell concentration (bacterial cell concentration) in the mixed solution of the metal dissolution solution and Torulopsis glabrata can be appropriately set according to the concentration of rare earth element ions adsorbed onto Torulopsis glabrata. For example, it can be set in the range of 1.0×10 6 cells / m 3 ~1.0×10 18 cells / m 3 Preferably, it is in the range of 1.0×10 10 cells / m 3 ~1×10 16 cells / m 3 More preferably, it is in the range of 1.0×10 12 cells / m 3 ~1×10 16 cells / m 3 。

[0114] The adsorption step may be a step of continuously supplying the metal solution and Torulaspora globosa to a mixing tank and continuously withdrawing a mixed solution containing the metal solution and the yeast from the mixing tank. By making the supply amount and the withdrawal amount the same, the adsorption treatment can be continuously performed. The average residence time in the steady state can be appropriately set according to the conditions of the aforementioned adsorption step.

[0115] In the separation step in the embodiment of the present invention, Torulaspora globosa adsorbed with rare earth element ions is separated from the mixed solution of the metal solution and Torulaspora globosa.

[0116] This separation can be carried out by a usual method for solid-liquid separation, and examples thereof include centrifugal separation, filtration, membrane separation, and sedimentation separation. Two or more of these separation methods can also be combined.

[0117] In the recovery step after the separation step in the embodiment of the present invention, rare earth element ions are recovered from the Torulaspora globosa separated in the separation step.

[0118] The recovery of rare earth element ions adsorbed on Torulaspora globosa can be carried out by burning Torulaspora globosa and recovering the rare earth element ions adsorbed on the yeast as its concentrate. In addition, by subjecting Torulaspora globosa to acid treatment, the rare earth element ions adsorbed on Torulaspora globosa can be detached.

[0119] In the case of recovering rare earth element ions by acid treatment, as the acidic solution used in this acid treatment, an acidic solution of a strong acid such as hydrochloric acid, sulfuric acid, nitric acid, or aqua regia, which is adjusted to a lower pH value compared to the pH value of the adsorption treatment (the pH value of the mixed solution in the adsorption step), can be used. For example, hydrochloric acid (HCl aqueous solution) of 0.1 to 12 M can be preferably used.

[0120] The temperature of the acidic solution during acid treatment can be room temperature, for example, 5 to 35 °C, but to promote the detachment of rare earth element ions, it can be set to about 60 to 100 °C, for example.

[0121] In addition, the acid treatment can be carried out multiple times, and acid treatments with the same or different conditions (acid concentration, temperature) of the acid treatment can also be carried out.

[0122] In the case of burning Torulaspora globosa in the recovery step, the separated solid component containing Torulaspora globosa obtained by solid-liquid separation in the separation step can be heat-treated to burn Torulaspora globosa. The separated solid component containing Torulaspora globosa can be dried as needed to reduce the water content and then heat-treated.

[0123] The heat treatment for burning Torulaspora globosa can use a usual industrial furnace such as an incinerator, a firing furnace, or a combustion furnace. From the viewpoint of continuousization of a process suitable for industrialization, a rotary kiln is preferably used.

[0124] As the temperature for burning Torulaspora, any temperature at which Torulaspora can burn can be appropriately set. For example, it can be set to 300 °C or higher. From the perspective of enabling more complete burning of Torulaspora, it is preferably 400 °C or higher, and more preferably 500 °C or higher. On the other hand, from the perspectives of preventing oxidation of metals and energy costs, it is preferably 800 °C or lower, and more preferably 750 °C or lower.

[0125] The yeast supplied to the furnace can be in a wet state just after separation, or in a powder state after being dried after separation.

[0126] After the burned Torulaspora sublimates or is ashified, the rare earth element ions adsorbed on the Torulaspora can be recovered as its concentrate.

[0127] As described above, in the rare earth element recovery method according to the embodiment of the present invention, after preparing a metal dissolution solution (preferably after performing a leaching step), an adsorption step, a separation step, and a recovery step are sequentially performed.

[0128] These respective steps can be performed separately, but from the perspective of productivity, it is preferable to perform them continuously. In addition, the process including these steps can be repeated multiple times in a batch manner, but from the perspective of productivity, it is preferable to perform it continuously.

[0129] Hereinafter, the process of the rare earth element recovery method according to the embodiment of the present invention will be described using the drawings.

[0130] Figure 1 and Figure 2 Fig. shows a flow chart for explaining the rare earth element recovery method according to the embodiment of the present invention (in the case where the recovery step is performed by heat treatment). It should be noted that in the following description, Torulaspora will be simply referred to as "yeast".

[0131] First, in the leaching step, a leachate containing rare earth element ions is obtained to prepare a metal dissolution solution.

[0132] Next, this metal dissolution solution is mixed with yeast, and rare earth element ions are adsorbed onto the yeast under the conditions of a specified pH and temperature (adsorption step).

[0133] At this time, when the pH of the metal dissolution solution is not within the specified range, a pH regulator (acid or base) can be added to the metal dissolution solution before mixing with the yeast or the mixture after mixing with the yeast to adjust it to the specified range. Figure 2The case of adding a pH adjuster to the metal solution before mixing with yeast is shown. When the pH of the metal solution is within a specified range, pH adjustment of the metal solution may not be necessary. However, when the pH of the mixed solution changes and deviates from the specified range during the adsorption process, it is preferable to adjust the pH of the mixed solution. When the pH of the mixed solution during the adsorption process is not within the specified range, a pH adjuster (acid or base) can be added to the mixed solution to adjust it to the specified range.

[0134] After the metal solution is mixed with yeast and a specified time has elapsed (after the adsorption process ends), the mixed solution is subjected to solid-liquid separation to obtain a solid component (separated solid component) and a residual liquid (solid-liquid separation process).

[0135] Next, the obtained solid component is heat-treated to burn the yeast contained in the solid component, and the rare earth element ions adsorbed on the yeast are recovered as its concentrate (metal concentrate) (recovery process).

[0136] The solid component obtained by solid-liquid separation can be supplied to the heat treatment furnace after washing as needed. In addition, the solid component obtained by solid-liquid separation can also be supplied to the heat treatment furnace after being dried to reduce the moisture content.

[0137] It should be noted that in the case of performing the recovery process of rare earth element ions multiple times in a batch manner, for example, when continuously performing using the equipment described later, the residual liquid obtained by solid-liquid separation can be mixed with the metal solution before mixing with yeast as needed. Depending on the separation efficiency of the solid-liquid separation, the residual liquid can also be returned to the mixed solution in the solid-liquid separation process.

[0138] Figure 3 A schematic diagram showing a structural example of an apparatus capable of being used for the rare earth element recovery method according to an embodiment of the present invention is shown.

[0139] Figure 3 The apparatus shown has, as its main structure, a mixing tank 11 for performing the adsorption process, a solid-liquid separator 31 for performing the separation process, and a heat treatment furnace 51 for performing the recovery process. Between the solid-liquid separator 31 and the heat treatment furnace 51, a dryer 41 for drying the solid component (separated solid component) separated by the solid-liquid separator 31 is provided in order to efficiently burn the yeast in the heat treatment furnace 51. In addition, a dust collector 61 for recovering the powder in the exhaust gas is connected to the outlet side of the exhaust gas of the heat treatment furnace 51 (the supply port side of the separated solid component), and the exhaust gas that has passed through the dust collector 61 is sent by a blower 63 to a flare stack 64.

[0140] The mixing tank 11 is equipped with a stirrer 12 and a temperature control unit (not shown) for controlling the temperature inside the tank. By means of the stirrer 12, mixing can be carried out in such a way that yeast is evenly dispersed in the metal solution. As the temperature control unit, for example, a heat medium circulation system can be used, which includes a pipe arranged inside the tank and a temperature regulator for adjusting the temperature of the heat medium flowing in the pipe for cooling or heating.

[0141] The metal solution is supplied to the mixing tank 11 from the injection port 13 via the control valve 13b. In addition, the pH regulator is supplied to the mixing tank 11 from the injection port 15 via the control valve 15b.

[0142] After being stored in the storage part 21, the yeast is transferred to the feeder 23 by the air from the air pump 22 via a powder flow regulator such as a rotary valve directly below the storage part 21, and then is supplied into the mixing tank 11 from the yeast inlet 14 via a powder flow regulator such as a rotary valve directly below the feeder 23.

[0143] As the feeder 23, powder supply devices such as belt type, table type, screw type, vibration type, and rotary gravity type can be used.

[0144] The mixed liquid inside the tank can be drawn out from the extraction part 16 of the mixing tank 11, and the drawn mixed liquid is sent to the solid-liquid separator 31 by the liquid delivery pump 16p.

[0145] As the solid-liquid separator 31, a sedimentation separator, a centrifugal separator, a membrane separator, a filter, etc. can be used, or two or more of them can be combined.

[0146] In the case of using filtration such as pressure filtration or centrifugal filtration for solid-liquid separation, the particle size of the yeast is 1 μm to 50 μm, and the average particle size is very small, about 7 μm. Therefore, the air permeability of the filter cloth is preferably 30 cc / cm 2 / minute or less. However, if the air permeability of the filter cloth is reduced, the filtration time is very long. Therefore, it is preferably to have an appropriate air permeability. In addition, if the particle size of the yeast is small and the air permeability of the filter cloth is large, leakage may occur from the filter cloth. Therefore, in this case, it is preferable to supply the leaked slurry to the solid-liquid separator or to another batch of solid-liquid separators for reuse. Thus, the recovery loss of yeast can be reduced.

[0147] In order to reduce the leakage amount from the filter cloth, a filter aid can also be added to the mixed liquid. In the case of using a filter aid, it is preferable to use a filter aid such as cellulose that is derived from a biological source and can be fired in the downstream firing equipment. In addition, by using a filter aid, a reduction in the filtration time can also be expected.

[0148] As a point to note when using filter cloth, yeast has the property that it is more likely to pass through the filter cloth if it comes into contact with a solvent for a long time. This is thought to be because yeast fuses with the solvent or is subject to shear force through long-term stirring, resulting in an easy change in shape, and yeast under centrifugal force or the force generated by pressurization is likely to leak out through the mesh of the filter cloth. This property varies depending on the yeast concentration, but if the contact time is about several hours, the separation performance can be maintained. Therefore, it varies depending on the air permeability of the filter cloth, but the contact between yeast and the solvent is about several hours.

[0149] It should be noted that in the case of centrifugal filtration, if the centrifugal force is 600G, the separation of yeast adsorbed with rare earth element ions is sufficient, and it can be set to 500 - 700G, for example.

[0150] When using a centrifugal settler as a solid-liquid separator, the centrifugal force is preferably 600G or more. The preferred treatment time varies depending on the centrifugal force. If it is 600G, the treatment time is preferably 5 to 10 minutes. If it is 1000G or more, the treatment time is preferably about several minutes (for example, 1 to 4 minutes). When reducing the water content rate of the solid component after solid-liquid separation, it is preferable to make the centrifugal force 1000G or more.

[0151] On the other hand, depending on the subsequent process (for example, when wanting to wash the solid component after solid-liquid separation), multi-stage separation with the centrifugal force changed according to the purpose can also be carried out as follows: The solvent is roughly separated with a centrifugal force of about 600G, the cleaning liquid is added to the highly fluid solid component (filter cake) in a state of high water content for cleaning, and then the centrifugal force is increased for solid-liquid separation.

[0152] If the centrifugal force is 1000G or more, solid-liquid separation is sufficient even if the treatment time is within 1 minute, but if it is desired to keep the leakage of yeast into the filtrate stable within several percent, it is preferable to set the treatment time to several minutes.

[0153] When using a solution with a pH less than 2 in solid-liquid separation, it is preferable to use acid-resistant materials such as Teflon (registered trademark) coating, titanium, and Hastelloy (registered trademark). When using a solution with a pH of 3 or more or a pH of 4 or more, materials made of SUS can be used.

[0154] Regarding the extraction of the solid component (yeast) after solid-liquid separation, in either the case of centrifugal filtration or the case of centrifugal sedimentation, it can be pushed out by blowing air. However, in the case of solid-liquid separation under low centrifugal force conditions, sometimes the higher the viscosity of the solid component, the more difficult it is to discharge by blowing air. In this case, it is preferable to scrape manually. In the case of performing solid-liquid separation by increasing the centrifugal force and reducing the moisture content of the solid component, the solid component can be scraped automatically, and it becomes easier to automate the subsequent heat treatment process.

[0155] The residual liquid separated by the solid-liquid separator 31 can be mixed with the metal dissolution liquid before being supplied to the mixing tank 11 via the control valve 32b through the residual liquid reuse pipeline 32.

[0156] In addition, in the case of a large amount of yeast, the residual liquid separated by the solid-liquid separator 31 can also be returned to the solid-liquid separator 31 (not shown).

[0157] The solid component (separated solid component) separated by the solid-liquid separator 31 is transferred to the heat treatment furnace 51 after being dried by the dryer 41. As the dryer 41, a dryer used in ordinary powder drying such as a ventilation type or a rotary type can be used.

[0158] It is also possible to supply the separated solid component to the heat treatment furnace 51 without performing the drying treatment based on the dryer 41, and perform both the drying treatment and the heat treatment (combustion) of the separated solid component in the heat treatment furnace 51. However, from the viewpoint of improving the efficiency of the heat treatment, it is preferable to perform the drying treatment of the separated solid component in advance.

[0159] Especially in the case where the acidity of the separated solid component is high (for example, when the pH is 5 or less), it is preferable to perform the drying treatment in advance. By performing the drying treatment, the acidic components contained in the separated solid component can be removed, so that corrosion caused by the acid in the heat treatment furnace 51 can be prevented.

[0160] In addition, in the case where the acidity of the separated solid component is high (for example, when the pH is 5 or less), when it is supplied to the heat treatment furnace 51 without performing the drying treatment, it is preferable to wash the separated solid component in advance to reduce the acidity, preferably set it to pH 5.2 - 7 in advance, and more preferably set it to pH 6 - 7.

[0161] As the heat treatment furnace 51, an industrial furnace such as a usual incinerator or an electric furnace can be used, and there is no particular limitation as long as it can burn yeast. A rotary kiln is preferred. According to the rotary kiln, the drying of the separated solid component, the combustion of yeast, and the recovery of metal can be continuously performed.

[0162] The separated solid components supplied to the heat treatment furnace 51 (e.g., rotary kiln) are gradually conveyed while slowly rotating. On the other hand, through the combustion of air and fuel supplied from the side opposite to the supply side of the separated solid components, the gradually conveyed separated solid components are dried, and then the yeast in the solid components burns. As a result, the yeast sublimes or is ashed, and the rare earth element ions adsorbed to the yeast are recovered as its concentrate.

[0163] The exhaust gas from the heat treatment furnace 51 is sent to the flare stack 64 by the blower 63 via the dust collector 61. The powder recovered by the dust collector 61 is mixed with the separated solid components before being supplied to the heat treatment furnace 51 through the conveying pipeline 62 such as a belt conveyor. Since the recovered powder contains yeast adsorbed with rare earth element ions, the recovery rate of rare earth elements can be increased by mixing with the separated solid components.

[0164] Examples

[0165] Hereinafter, the present invention will be described in detail by way of examples and comparative examples, but the present invention is not limited to these examples.

[0166] (Chemical leaching treatment of rare earth element mud simulated solution)

[0167] As a simulated solution of the actual liquid assuming rare earth element mud, a slurry containing rare earth element mud (including seawater) was prepared, and this slurry was decanted three times using pure water.

[0168] The decanted precipitate (mud-like solid matter) was mixed with hydrochloric acid (HCl aqueous solution), and chemical leaching treatment was carried out under the following conditions.

[0169] Concentration of hydrochloric acid (HCl aqueous solution): 0.5 M (initial concentration)

[0170] Concentration of rare earth element mud: 10 w / v%

[0171] Temperature: room temperature

[0172] Treatment time, i.e., leaching time: 10 minutes, 60 minutes, 24 hours

[0173] After the above chemical leaching treatment, centrifugation (10 minutes) was carried out, and then the liquid phase was filtered through a filter with a pore size of 0.2 μm (30 minutes), and the pH of the filtered liquid phase (leachate) was adjusted.

[0174] At this time, a 50 wt% NaOH aqueous solution was used as the pH adjuster, and the initial pH of the leachate was adjusted to pH 0.4, pH 1.0, pH 1.5, and pH 2.0 respectively, and left standing overnight.

[0175] The metal components in the liquid (leachate) obtained by ICP (Inductively Coupled Plasma) optical emission spectrometry are summarized in Tables 1 and 2. Table 1 shows the composition of the leachate adjusted to each pH (leaching time: 10 minutes), and Table 2 shows the composition of the leachate adjusted to pH 0.4 (leaching times: 10 minutes, 60 minutes, 24 hours).

[0176] Sc, Lu, and Tm are below the detection limit.

[0177]

[0178] "nd" in the table indicates below the detection limit.

[0179]

[0180] "-" in the table indicates not measured.

[0181] (Example 1)

[0182] As described above, a chemical leaching treatment (leaching time: 10 minutes) was performed on the simulated solution of rare earth element mud to prepare a leachate of rare earth elements (pH 2.0).

[0183] 40 mg of commercially available Torulaspora (manufactured by KOHJIN Life Sciences Co., Ltd., product name: KR yeast) (content of dry yeast: 8 g / L) was mixed with 5 ml of the prepared leachate at pH 2.0, and the mixture was subjected to shaking and stirring in an incubator (34 °C) for 30 minutes (adsorption step), and then filtered through a filter with a pore size of 0.2 μm. The pH of the filtrate (liquid phase) was 2.2.

[0184] The metal ion concentrations in the filtrate (liquid phase) were measured by ICP (Inductively Coupled Plasma) optical emission spectrometry. The results are shown in Table 3. The values in parentheses in the table indicate the adsorption rate.

[0185] It should be noted that the adsorption rate of each metal ion was calculated according to the following formula.

[0186] Adsorption rate (%) = (Metal ion concentration in the leachate before adding yeast - Metal ion concentration in the filtrate) / Metal ion concentration in the leachate before adding yeast × 100

[0187] (Comparative Example 1)

[0188] Except for using Torulaspora instead of baker's yeast (manufactured by Oriental Yeast Co., ltd., trade name: Dry Yeast 500G), the metal ion adsorption treatment (adsorption process) was carried out in the same manner as in Example 1, and the metal ion concentration in the filtrate (liquid phase) was measured by ICP. The results are shown in Table 3.

[0189] (Example 2)

[0190] Except for changing the content of Torulaspora to 16 g / L, the metal ion adsorption treatment (adsorption process) was carried out in the same manner as in Example 1, and the metal ion concentration in the filtrate (liquid phase) was measured. The results are shown in Table 3.

[0191] (Comparative Example 2)

[0192] Except for using Torulaspora instead of baker's yeast (manufactured by Oriental Yeast Co., ltd., trade name: Dry Yeast 500G), the metal ion adsorption treatment was carried out in the same manner as in Example 2, and the metal ion concentration in the filtrate (liquid phase) was measured. The results are shown in Table 3.

[0193]

[0194] (Example 3)

[0195] Except for using a leaching solution with pH 1.0, the metal ion adsorption treatment (adsorption process) was carried out in the same manner as in Example 1, and the metal ion concentration in the filtrate (liquid phase) was measured. The pH of the filtrate (liquid phase) was 1.1. The results are shown in Table 4. The values in parentheses in the table represent the adsorption rate.

[0196] (Example 4)

[0197] Except for using a leaching solution with pH 1.0, the metal ion adsorption treatment (adsorption process) was carried out in the same manner as in Example 2, and the metal ion concentration in the filtrate (liquid phase) was measured. The pH of the filtrate (liquid phase) was 1.2. The results are shown in Table 4.

[0198] (Example 5)

[0199] Except for using a leaching solution with pH 1.5, the metal ion adsorption treatment (adsorption process) was carried out in the same manner as in Example 1, and the metal ion concentration in the filtrate (liquid phase) was measured. The pH of the filtrate (liquid phase) was 1.6. The results are shown in Table 4.

[0200] (Example 6)

[0201] Except for using the leaching solution with pH 1.5, the adsorption treatment (adsorption process) of metal ions was carried out in the same manner as in Example 2, and the metal ion concentration in the filtrate (liquid phase) was measured. The pH of the filtrate (liquid phase) was 1.6. The results are shown in Table 4.

[0202]

[0203] (Example 7) Desorption treatment of rare earth element ions adsorbed on Torulaspora globosa

[0204] The solid component (Torulaspora globosa adsorbed with rare earth element ions) in the mixture after the adsorption treatment (adsorption process) of Example 2 was washed with water. Specifically, the mixture after the adsorption treatment (adsorption process) was subjected to solid-liquid separation at 3000G for 10 minutes using a centrifuge, the obtained solid component was mixed with pure water, and stirred using a vortex mixer, and a total of 3 water washing treatments were performed.

[0205] The solid component after the water washing treatment was subjected to desorption treatment by stirring in a 0.2M HCl aqueous solution at room temperature for 3 minutes using a vortex mixer. A part of the obtained mixture was collected, filtered through a filter with a pore size of 0.2 μm, and the metal ion concentration in the filtrate (liquid phase) was measured by ICP emission spectrometry to obtain the metal ion desorption amount (mg) based on the 0.2M HCl aqueous solution.

[0206] Next, the mixture after the desorption treatment was subjected to solid-liquid separation at 3000G for 10 minutes using a centrifuge, and the obtained solid component was stirred in concentrated hydrochloric acid at 12M at 90 °C for 30 minutes using a vortex mixer for another desorption treatment. A part of the obtained mixture was collected, filtered through a filter with a pore size of 0.2 μm, and the metal ion concentration in the filtrate (liquid phase) was measured by ICP emission spectrometry to obtain the metal ion desorption amount (mg) based on concentrated hydrochloric acid.

[0207] The obtained results are shown in Table 5. It should be noted that the "amount of metal ions adsorbed on yeast in Example 2 (mg)" in the table is a value calculated from the measured value of the composition of the leaching solution with pH 2.0 and the measured value of the composition of the liquid phase after the adsorption treatment in Example 2.

[0208] From the results shown in Table 3 and Table 4, it can be seen that according to the embodiment of the present invention, rare earth elements can be recovered using Torulaspora globosa under acidic conditions.

[0209] In addition, from the results shown in Table 3, it can be seen that Torulaspora globosa has a higher adsorption rate of rare earth element ions compared to baker's yeast, and according to the embodiment of the present invention, rare earth elements can be recovered efficiently.

[0210] Furthermore, as can be seen from the results shown in Table 5, the rare earth element ions adsorbed on Torulaspora globosa can be easily detached by treatment with hydrochloric acid.

[0211]

[0212] (Chemical leaching treatment of the actual liquid of rare earth element mud)

[0213] The following chemical leaching treatment was carried out using the actual rare earth element mud.

[0214] The rare earth element mud used was the rare earth element mud without pretreatment such as strong acid decomposition and evaporation to dryness.

[0215] The rare earth element mud was mixed with 0.5 M hydrochloric acid (HCl aqueous solution), and the concentration of the rare earth element mud was adjusted to 40 w / v%. It was stirred with a stirring blade at room temperature for 60 minutes.

[0216] Then, centrifugation was carried out, and then the liquid phase was filtered through a filter with a pore size of 0.2 μm.

[0217] The metal components in the liquid (leaching solution) obtained by ICP (Inductively Coupled Plasma) optical emission spectrometry were measured. The measurement results are shown in Table 6.

[0218]

[0219] (Example 8)

[0220] As described above, after the chemical leaching treatment (leaching time: 60 minutes) of the actual liquid of rare earth element mud, centrifugation (10 minutes) was carried out, and then the liquid phase was filtered through a filter with a pore size of 0.2 μm. The pH of the filtered liquid phase (leaching solution) was adjusted. At this time, a 50 wt% NaOH aqueous solution was used as the pH adjuster, and the initial pH of the leaching solution was adjusted to pH 1.0 and left standing overnight.

[0221] 80 mg of commercially available Torulaspora globosa (manufactured by KOHJIN Life Sciences Co., Ltd., product name: KR yeast) (content of dry yeast: 16 g / L) was mixed with 5 ml of the leaching solution with an initial pH of 1.0, and the mixture was shaken and stirred in an incubator (34 °C) for 30 minutes (adsorption step), and then filtered through a filter with a pore size of 0.2 μm. The pH of the filtrate (liquid phase) was 1.0.

[0222] The metal ion concentration in the filtrate (liquid phase) obtained by ICP (Inductively Coupled Plasma) optical emission spectrometry was measured. The results are shown in Table 7. The values in parentheses in the table represent the adsorption rate.

[0223] It should be noted that the adsorption rate of each metal ion is calculated according to the following formula.

[0224] Adsorption rate (%) = (Metal ion concentration in the leachate before adding yeast - Metal ion concentration in the filtrate) / Metal ion concentration in the leachate before adding yeast × 100

[0225] (Example 9)

[0226] Except that the leachate adjusted to pH 1.0 is used instead of the leachate adjusted to pH 2.0, the adsorption treatment of metal ions (adsorption step) is carried out in the same manner as in Example 8, and the metal ion concentration in the filtrate (liquid phase) is measured. The results are shown in Table 7.

[0227] (Comparative Examples 3 - 5)

[0228] Except that Torulaspora utilis is used instead of baker's yeast (Comparative Example 3), halotolerant yeast 1 (Comparative Example 4: C. krusei (normal culture)), and halotolerant yeast 2 (Comparative Example 5: C. krusei (high-salt culture)) respectively, the adsorption treatment of metal ions (adsorption step) is carried out in the same manner as in Example 8, and the metal ion concentration in the filtrate (liquid phase) is measured. The results are shown in Table 7.

[0229] It should be noted that high-salt culture is usually carried out by adding NaCl to the culture medium (NaCl concentration 10%).

[0230] (Comparative Examples 6 - 8)

[0231] Except that Torulaspora utilis is used instead of baker's yeast (Comparative Example 6), halotolerant yeast 1 (Comparative Example 7: C. krusei (normal culture)), and halotolerant yeast 2 (Comparative Example 8: C. krusei (high-salt culture)) respectively, the adsorption treatment of metal ions (adsorption step) is carried out in the same manner as in Example 9, and the metal ion concentration in the filtrate (liquid phase) is measured. The results are shown in Table 7.

[0232]

[0233] From the results shown in Table 7, it can be seen that according to the embodiments of the present invention, Torulaspora utilis can also be used to recover rare earth elements from actual rare earth element mud.

[0234] In addition, from the results shown in Table 7, it can be seen that compared with other yeasts, the adsorption rate of rare earth elements to Torulaspora utilis is high, and according to the embodiments of the present invention, rare earth elements can be efficiently recovered.

[0235] Description of reference numerals:

[0236] 11 Mixing tank

[0237] 12 Stirrer

[0238] 13 Metal dissolution liquid inlet

[0239] 13b Metal dissolution liquid injection control valve

[0240] 14 Yeast inlet

[0241] 15 pH regulator inlet

[0242] 15b pH regulator injection control valve

[0243] 16 Mixed liquid extraction section

[0244] 16p Mixed liquid feed pump

[0245] 21 Storage section

[0246] 22 Air pump

[0247] 23 Feeder

[0248] 31 Solid-liquid separator

[0249] 32 Residual liquid recycling pipeline

[0250] 32b Residual liquid control valve

[0251] 41 Dryer

[0252] 44 Heat treatment furnace

[0253] 61 Dust collector

[0254] 62 Conveyor pipeline for recycled powder (belt conveyor)

[0255] 63 Blower

[0256] 64 Torch chimney

[0257] FIC: Flow indicator controller

[0258] MCC: Motor control center

[0259] M: Prime mover.

Claims

1. A method for recovering rare earth elements, wherein, the method for recovering rare earth elements includes: an adsorption step of mixing a liquid containing rare earth element ions with Torulaspora globosa to obtain a mixed liquid in which the rare earth element ions are adsorbed to the Torulaspora globosa under acidic conditions; a separation step of separating the Torulaspora globosa from the mixed liquid obtained in the adsorption step; and a recovery step of recovering the rare earth element ions from the Torulaspora globosa separated in the separation step.

2. The method for recovering rare earth elements according to claim 1, wherein, the pH of the mixed liquid in the adsorption step is 1.0 or higher.

3. The method for recovering rare earth elements according to claim 1, wherein, the pH of the mixed liquid in the adsorption step is 2.4 or lower.

4. The method for recovering rare earth elements according to claim 1, wherein, the method for recovering rare earth elements further includes a leaching step of treating a solid material containing rare earth elements with an acidic liquid to leach rare earth element ions to obtain an acidic liquid containing rare earth element ions, and mixing the acidic liquid obtained in the leaching step with Torulaspora globosa to perform the adsorption step.

5. The method for recovering rare earth elements according to claim 4, wherein, the pH of the acidic liquid used in the leaching step is 2.0 or lower.

6. The method for recovering rare earth elements according to claim 4, wherein, the solid material containing rare earth elements is a rare earth element-containing mineral.

7. The method for recovering rare earth elements according to claim 4, wherein, the solid material containing rare earth elements is apatite, iron hydroxide or manganese oxide containing rare earth elements.

8. The method for recovering rare earth elements according to claim 4, wherein, the solid material containing rare earth elements is rare earth element sludge.

9. The method for recovering rare earth elements according to claim 1, wherein, the liquid before mixing with Torulaspora globosa further contains ions of metals other than rare earth elements.

10. The method for recovering rare earth elements according to claim 4, wherein, the solid material containing rare earth elements further contains metals other than rare earth elements, and the liquid before mixing with Torulaspora globosa further contains ions of metals other than rare earth elements.

11. The method for recovering rare earth elements according to claim 9 or 10, wherein, the metal other than rare earth elements is at least one selected from vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, magnesium, aluminum, calcium, titanium.

12. The method for recovering rare earth elements according to claim 4, wherein, in the leaching step, the treatment time with the acidic liquid, i.e., the leaching time, is within 1 hour.

13. The method for recovering rare earth elements according to claim 1, wherein, the adsorption step is a step of continuously supplying the liquid and the Torulaspora globosa to a mixing tank and continuously extracting a mixed liquid containing the liquid and the Torulaspora globosa from the mixing tank.

14. The method for recovering rare earth elements according to claim 1, wherein, the separation step is a step of performing solid-liquid separation on the mixed liquid obtained in the adsorption step to obtain a separated solid component, The recovery step is a step of subjecting the separated solid component obtained in the separation step to acid treatment to recover the rare earth element ions adsorbed on the Torulaspora globosa.

15. The method for recovering rare earth elements according to claim 1, wherein the separation step is a step of performing solid-liquid separation on the mixed liquid obtained in the adsorption step to obtain a separated solid component, the recovery step is a step of subjecting the separated solid component obtained in the separation step to heat treatment and burning the Torulaspora globosa to recover the rare earth element ions adsorbed on the Torulaspora globosa as its concentrate.

16. The method for recovering rare earth elements according to claim 15, wherein in the recovery step, the heat treatment of the separated solid component is carried out by firing in an industrial furnace.

17. The method for recovering rare earth elements according to claim 15 or 16, wherein powder is recovered from the exhaust gas of the heat treatment step, and the recovered powder is mixed with the separated solid component before the heat treatment step.

18. The method for recovering rare earth elements according to claim 14 or 15, wherein the solid-liquid separation is carried out by at least one selected from centrifugal separation, filtration, membrane separation, and sedimentation separation.

19. The method for recovering rare earth elements according to claim 14 or 15, wherein the method for recovering rare earth elements further includes a drying step of reducing the moisture content of the separated solid component.

20. The method for recovering rare earth elements according to claim 14 or 15, wherein the separated liquid component obtained by solid-liquid separation in the separation step is mixed with the liquid containing the rare earth element ions before mixing the Torulaspora globosa.

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