Metal recovery methods

Abstract

Provided is a metal recovering method that has a low environmental load and that can efficiently achieve recovery of metal at a low cost. A metal recovering method comprising: an adsorption step for mixing yeast with a liquid containing metal ions and causing the metal ions to be adsorbed to the yeast in the obtained mixture solution; an isolation step for isolating the yeast from the mixture solution obtained in the adsorption step; and a recover step for recovering metal ions from the yeast isolated in the isolation step, wherein the metal ions to be adsorbed to the yeast in the adsorption step are rare-earth element ions and / or noble metal ions.

Description

[Technical Field] 【0001】 This invention relates to a method for recovering metal. [Background technology] 【0002】 In recent years, biosorption, a method of recovering metals using biological materials such as microorganisms as adsorbents, has been explored. By using inexpensive biological materials, it is expected to be a low-cost and environmentally friendly method for recovering metals from low-grade minerals, factory wastewater, and electronic equipment waste. 【0003】 Various technologies have been proposed for recovering precious metals and rare earth elements using biosorption methods like this. 【0004】 For example, Patent Document 1 discloses a method for recovering precious metals, comprising the steps of contacting baker's yeast with precious metal ions in a liquid with a pH of 4 or lower containing precious metal ions, and calcining the yeast separated from the liquid. Specifically, it describes examples of recovering gold ions, platinum ions, and palladium ions as precious metal ions, and also states that platinum ions can be recovered from a liquid with a pH of 1.2 in which chromium ions are present. 【0005】 Patent Document 2 discloses a method for recovering gold, which includes the steps of contacting yeast with a solution containing gold ions, iron ions, copper ions, and halide ions under acidic conditions, performing solid-liquid separation, and calcining a mixture containing baker's yeast and gold. Examples of solution pH conditions such as pH < 0, pH 0.55, and pH 1.12 are described. 【0006】 Patent Document 3 discloses a method for recovering rare earths, which includes a step of mixing a solution containing rare earths with white seeds to adsorb the rare earths onto the white seeds (the pH of the mixed solution is preferably 3 or more, more preferably about pH 4), a step of recovering the white seeds from the mixed solution, and a step of separating the rare earths from the white seeds by adding an acidic solution to the recovered white seeds. It is also described that Nd and Dy can be selectively recovered from a solution in which Fe coexists. 【0007】 Non-Patent Document 1 describes that by modifying baker's yeast with phosphate, the adsorption amounts of heavy metal ions such as Cd 2+ 、Cu 2+ 、Pb 2+ 、Zn 2+ can be increased compared with baker's yeast not modified with phosphate. It is also described that phosphate-modified baker's yeast can efficiently adsorb rare earth ions such as Ce 3+ 、Dy 3+ 、Gd 3+ 、La 3+ 、Nd 3+ 、Y 3+ 、Yb 3+ . Furthermore, it is described that phosphate-modified baker's yeast can selectively adsorb rare earth ions (Nd 3+ and Yb 3+ ) from an aqueous solution containing heavy metals and rare earth ions. 【Prior Art Documents】 【Patent Documents】 【0008】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2016-183371 【Patent Document 2】 Japanese Patent Application Laid-Open No. 2018-35413 【Patent Document 3】 Japanese Patent Application Laid-Open No. 2013-213272 【Non-Patent Documents】 【0009】 【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 [Overview of the Initiative] [Problems that the invention aims to solve] 【0010】 Conventional metal recovery methods that do not use biological materials have problems with high environmental impact due to CO2 emissions and sludge treatment. Furthermore, conventional metal recovery methods using biological materials require further improvement in recovery rate and / or selectivity. In addition, the recovery methods described in Patent Documents 1-3 and Non-Patent Document 1 are batch-based and at the laboratory level, resulting in low productivity. 【0011】 The recovery method described in Non-Patent Document 1 has the problem of high costs associated with the adsorbent because it requires chemical modification of the yeast used as the adsorbent. 【0012】 The object of the present invention is to solve the problems seen in view of the above circumstances and to provide a low-environmental-impact metal recovery method that can recover metals at low cost and efficiently. Another object of the present invention is to provide a highly productive, low-environmental-impact metal recovery method suitable for industrialization. [Means for solving the problem] 【0013】 The present invention has the following aspects. [1] An adsorption step in which a liquid containing metal ions is mixed with yeast, and the metal ions are adsorbed onto the yeast in the resulting mixture, A separation step is performed to separate the yeast from the mixture obtained in the adsorption step, The process includes a recovery step of recovering the metal ions from the yeast separated in the separation step, A method for recovering metals, wherein the metal ions adsorbed by yeast in the adsorption step are rare earth ions and / or precious metal ions. [2] The metal ion is a rare earth ion, The method for recovering metal according to item 1, wherein the pH of the mixed solution in the adsorption step is 2.5 or more and less than 7. [3] The metal ion is a noble metal ion, The method for recovering a metal according to item 1, wherein the pH of the mixed solution in the adsorption step is less than 4. [4] The method for recovering a metal according to item 1 or 2, wherein the metal ion comprises an Nd ion or a Dy ion. [5] The method for recovering a metal according to item 1 or 3, wherein the metal ion includes a gold ion. [6] The method for recovering metals according to any one of items 1 to 5, wherein the liquid before mixing with yeast further contains ions of metals other than rare earths or precious metals. [7] The method for recovering metals as described in paragraph 6, wherein the metal other than rare earths or precious metals is at least one selected from iron, copper, nickel, aluminum, manganese, magnesium, and zinc. [8] The method for recovering metals according to paragraph 6 or 7, wherein the metal ions are noble metal ions, and in the adsorption step, a metal ion chelating agent that binds to metal ions other than noble metals is added to the liquid or mixture before mixing with yeast. [9] The method for recovering metals according to paragraph 8, wherein the metal ion sequestering agent is citric acid or a salt thereof.

[10] The method for recovering a metal according to any one of items 1 to 9, wherein the yeast is baker's yeast.

[11] The method for recovering a metal according to any one of items 1 to 10, wherein the adsorption step is a step of continuously supplying the liquid and the yeast to a mixing tank and continuously withdrawing the mixture containing the liquid and the yeast from the mixing tank.

[12] The separation step is a step of obtaining separated solids by solid-liquid separation of the mixed liquid obtained in the adsorption step, The method for recovering metals according to any one of items 1 to 11, wherein the recovery step is a step of treating the separated solids obtained in the separation step with acid to recover the metal ions adsorbed on the yeast.

[13] The separation step is a step of obtaining separated solids by solid-liquid separation of the mixed liquid obtained in the adsorption step, A method for recovering metals according to any one of claims 1 to 11, wherein the recovery step is a step of heat-treating the separated solid obtained in the separation step to burn the yeast and recover the metal ions adsorbed on the yeast as a concentrate.

[14] The method for recovering metal according to item 13, wherein the heat treatment of the separated solids in the recovery step is performed by firing in an industrial furnace.

[15] A method for recovering metal according to item 13 or 14, comprising recovering powder from the exhaust gas of the heat treatment process and mixing the recovered powder with the separated solids before the heat treatment process.

[16] The method for recovering a metal according to any one of items 12 to 15, wherein the solid-liquid separation is carried out by at least one selected from centrifugation, filtration, membrane separation, and sedimentation.

[17] A method for recovering metal according to any one of claims 12 to 16, further comprising a drying step to reduce the moisture content of the separated solids.

[18] A method for recovering metal according to any one of items 12 to 17, wherein the separated liquid obtained in the solid-liquid separation of the separation step is mixed with the liquid containing metal ions before the yeast is mixed in. [Effects of the Invention] 【0014】 According to embodiments of the present invention, a metal recovery method can be provided that enables low-cost and efficient metal recovery. Furthermore, according to other embodiments of the present invention, a highly productive metal recovery method suitable for industrialization can be provided. Moreover, according to these embodiments, a metal recovery method with a lower environmental impact than conventional methods can be provided. [Brief explanation of the drawing] 【0015】 [Figure 1]This is a block flow diagram illustrating one embodiment of the metal recovery method of the present invention. [Figure 2] This is a block flow diagram illustrating another embodiment of the metal recovery method of the present invention. [Figure 3] This is a schematic diagram showing an example of the configuration of equipment that can be used in one embodiment of the metal recovery method of the present invention. [Figure 4] This is a schematic diagram of an example of equipment configuration that can be used in other embodiments of the metal recovery method of the present invention. [Figure 5] This figure shows the adsorption effect (over time) of metal ions (Dy ions) from a metal dissolution solution by yeast. [Figure 6] This figure shows the pH-dependent adsorption effect of yeast on metal ions (Dy ions) from metal dissolution solutions. [Figure 7] This figure shows the adsorption effect (over time) of yeast on metal ions (Nd ions and Dy ions) from a metal dissolution solution. [Modes for carrying out the invention] 【0016】 Preferred embodiments of the present invention will be described below. In the following explanation, the "liquid containing metal ions" before mixing with yeast will also be referred to as "metal dissolving solution" as appropriate. 【0017】 The yeast that can be used in the embodiments of the present invention is not particularly limited as long as it is capable of adsorbing metal ions (preferably rare earth ions or precious metal ions) to be recovered, but baker's yeast is preferred. Yeast, especially baker's yeast, is readily available and easy to handle, thus reducing costs. Furthermore, in the embodiments of the present invention, the adsorption rate of metal ions to the yeast is fast, which increases the processing efficiency of the metal solution, and consequently reduces the capacity of the mixing tank used to mix the metal solution and yeast, and also allows for miniaturization of the recovery device used in the embodiments of the present invention. 【0018】 The yeast used in the embodiments of the present invention has an isoelectric point in the range of pH 3.5 to 4.5. For example, baker's yeast has an isoelectric point around pH 4. By using yeast with such an isoelectric point, the recovery rate can be increased, or both the recovery rate and selectivity can be increased, by controlling the pH of the yeast-containing mixture in the adsorption process to a predetermined range. Even if the isoelectric point of the yeast is outside the range of pH 3.5 to 4.5, the recovery rate and selectivity of the metal can be controlled by controlling the pH according to its isoelectric point. 【0019】 As for yeasts known as baker's yeast, yeasts of the genus Saccharomyces are preferred, and Saccharomyces cerevisiae is more preferred. Saccharomyces yeasts are representative budding yeasts, including, for example, S. bayanus, S. boulardii, S. bulderi, S. cariocanus, S. cariocus, S. cerevisiae, S. chevalieri, S. dairenensis, S. ellipsoideus, S. florentinus, S. kluyveri, S. martiniae, S. monacensis, S. norbensis, S. paradoxus, S. pastorianus, S. spencerorum, S. turicensis, S. unisporus, S. uvarum, and S. zonatus. 【0020】 Other yeasts that can be used in embodiments of the present invention include, for example, yeasts of the genera Candida, Torulopsis, Zygosaccharomyces, Schizosaccharomyces, Pichia, Yarrowia, Hansenula, Kluyveromyces, Debaryomyces, Geotrichum, Wickerhamia, Fellomyces, and Sporobolomyces. 【0021】 The yeast used in the embodiments of the present invention does not need to be alive; dead yeast, such as discarded yeast, can be used as long as its metal ion adsorption function is not inhibited. Using dead yeast, such as discarded yeast, not only reduces costs but also reduces the environmental impact as determined by Life Cycle Assessment (LCA). Furthermore, while live yeast is affected by environmental factors (for example, yeast activity stops when the outside temperature is low), the influence of environmental factors is minimal because dead yeast can be used. 【0022】 In the metal recovery method of the embodiment of the present invention, the metal to be recovered is one that can be adsorbed by yeast in a state in which it is contained in a solution as metal ions, and rare earth elements or precious metals are preferred. 【0023】 The rare earth elements mentioned above are also called "rare earth elements" and consist of scandium (Sc), yttrium (Y), and lanthanides (the 15 elements from lanthanum (La) to lutetium (Lu) in the periodic table). In other words, 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). 【0024】 The precious metals listed above are gold (Au), silver (Ag), platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), and osmium (Os). 【0025】 In embodiments of the present invention, the liquid containing metal ions (metal dissolving solution) is a liquid containing ions of at least one metal selected from the above metals (the above rare earth elements and / or the above precious metals). 【0026】 In the metal recovery method of the embodiment of the present invention, the metal dissolving solution is not particularly limited as long as it contains ions of the metal to be recovered. However, if the metal to be recovered includes rare earth elements, a liquid containing ions of at least one rare earth element selected from the 15 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. Preferably, a liquid containing ions of at least one rare earth element selected from Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu can be used, and more preferably, a liquid containing at least Nd ions or Dy ions can be used. 【0027】 Furthermore, in the metal recovery method of the embodiment of the present invention, the metal dissolving solution is not particularly limited as long as it contains ions of the metal to be recovered. However, if the metal to be recovered includes precious metals, for example, a liquid containing at least one selected from gold ions, platinum ions, and palladium ions can be used, and a liquid containing at least gold ions can be used. 【0028】 Furthermore, in the metal recovery method of the embodiment of the present invention, the metal dissolving solution may contain heavy metal ions as ions of metals other than rare earths and precious metals (metals not intended for recovery), and examples of heavy metal ions include ions of heavy metals such as chromium, manganese, iron, cobalt, nickel, copper, and zinc. In addition, the metal dissolving solution in the embodiment of the present invention may contain ions of light metals such as aluminum, magnesium, and titanium. 【0029】 In embodiments of the present invention, the solvent for the metal dissolution solution is preferably an aqueous solvent or an aqueous solvent containing water, and may also contain water-soluble solvents other than water, as long as it does not impair adsorption by yeast. Examples of water-soluble solvents include alcohols such as methanol, ethanol, and propanol, acetone, acetonitrile, dioxane, tetrahydrofuran, dimethylformamide, dimethylacetamide, and dimethyl sulfoxide. The water content in this solvent is preferably 70 to 100% by volume, more preferably 80 to 100% by volume, and even more preferably 90 to 100% by volume, and this solvent is particularly preferably water. 【0030】 The metal dissolving solution (liquid to be mixed with yeast) in the embodiments of the present invention can be prepared by processing a material from which metal ions can be extracted (hereinafter referred to as "recoverable material"). The materials to be recovered are not particularly limited as long as metal ions can be extracted, and include solids or liquids containing metals, metal ions, or salts thereof. For example, if the material to be recovered is an urban mine such as rare earth soil, mineral resources, alloys, metal scrap, spent catalysts, or discarded electronic equipment, an acid treatment can be performed to obtain a metal dissolving solution. If the material to be recovered is factory wastewater or mine drainage, a metal dissolving solution can be obtained by dilution or concentration, solvent replacement, or pH adjustment as needed. If the material to be recovered contains metals, their ions, or salts that are not intended for recovery, the liquid obtained from that material may also contain ions of the metals not intended for recovery. It is preferable to remove insoluble matter from the metal dissolution solution obtained by processing the recovered material before mixing it with yeast. 【0031】 The metal recovery method according to the embodiment of the present invention is an industrially useful technology for recovering metals from sources such as soil including rare earth mud, urban mines containing mineral resources, alloys, metal scrap, spent catalysts, and discarded electronic equipment, factory wastewater, mine drainage, and metal solutions containing low concentrations of metal ions after recycling. 【0032】 To adjust the pH of the metal dissolution, an acid such as hydrochloric acid or sulfuric acid, or an alkali such as an aqueous sodium hydroxide solution, may be added as a pH adjuster before mixing in the yeast. Alternatively, after mixing the metal dissolution and yeast, an acid such as hydrochloric acid or sulfuric acid, or an alkali such as an aqueous sodium hydroxide solution, may be added as a pH adjuster to adjust the pH of the resulting mixture. 【0033】 In the adsorption step according to the embodiment of the present invention, a metal dissolution solution and yeast are mixed, and the metal ions are adsorbed onto the yeast in the resulting mixture. The adsorption step can be carried out under atmospheric pressure conditions. To further enhance the adsorption effect of metal ions onto yeast, it is preferable that the pH of this mixture be within a suitable pH range corresponding to the type of metal to be recovered. By ensuring that the pH of the above-mentioned mixture in the adsorption process is within a pH range corresponding to the type of metal to be recovered, the amount of metal ions adsorbed onto the yeast (recovery rate) and / or selectivity can be increased. Furthermore, the pH of this mixture is preferably -1 or higher, more preferably 0 or higher, even more preferably 1 or higher, preferably less than 7, and more preferably 6.5 or lower. 【0034】 In particular, when the metal ions adsorbed by the yeast are rare earth ions, the pH of the above mixture can be set to 2.5 or higher, preferably 2.7 or higher, more preferably 3 or higher, even more preferably 4 or higher, and especially preferably 5 or higher. The upper limit of pH is not particularly limited, but from the viewpoint of preventing rare earth ions from forming hydroxides and precipitating, it is preferably acidic to less than 7, and more preferably 6.5 or lower. By adjusting the pH of the above mixture, it is possible to improve the recovery rate of rare earth ions and increase the selectivity of rare earth ions for adsorption onto metal ions that are not intended for recovery. For example, a high selectivity of rare earth ions for divalent metal ions such as Mn, Zn, and Mg can be expected. For metal ions whose adsorption rate increases over time, such as Cu ions, the selectivity of rare earth ions can be further increased by adjusting the time of the adsorption process (adsorption time) as described later. Furthermore, high selectivity for rare earth ions can be expected even against metal ions that precipitate due to pH adjustment. For example, trivalent Fe ions precipitate as hydroxides when the pH is adjusted, and the Fe ion concentration in the liquid phase decreases. This reduces the amount of Fe ions adsorbed onto yeast, thereby increasing the selectivity for the target rare earth ions. 【0035】 On the other hand, if the metal ions to be adsorbed by the yeast are noble metal ions, it is more preferable that the pH of the above mixture be less than 4. When the pH of the above mixture is less than 4, it is possible to improve the selectivity in addition to improving the recovery rate of the noble metal ions. 【0036】 The reason why the adsorption of metal ions by yeast is affected by pH is presumed to be as follows: Since the isoelectric point of yeast is around pH 4, under conditions where the pH is less than 4, the surface of the yeast will have more positively charged functional groups, and under conditions where the pH is 4 or higher, the surface of the yeast will have more negatively charged functional groups. For example, rare earth ions are cations with a high charge (for example, Dy 3+ , Nd 3+ Since they exist in the liquid in the state of (), when recovering rare earth ions, it is preferable that there are few positively charged functional groups on the surface of the yeast, that is, conditions at pH 3 or higher with few positively charged functional groups are preferable, conditions at pH 4 or higher near the isoelectric point are more preferable, conditions at pH 5 or higher with many negatively charged functional groups are preferable, and conditions at pH 5.5 or higher are even more preferable. When recovering rare earth ions, the pH of the mixed liquid in the adsorption step can be set to, for example, pH 2.5 or higher (preferably pH 4 or higher) and pH less than 7 (preferably pH 6.5 or lower). 【0037】 On the other hand, noble metal ions form anionic complexes (e.g., [AuCl4]) at pH 4 or below. - [PtCl6] 2- Because they form a compound, they are more easily adsorbed under conditions of pH less than 4, where there are more positively charged functional groups. In fact, since noble metal ions are sufficiently adsorbed by yeast at pH less than 4, it is preferable to adjust the pH of the mixture containing yeast to less than 4. When recovering noble metal ions, the pH of the mixture in the adsorption step can be set to, for example, pH -1 or higher (preferably pH 0 or higher) and less than pH 4 (preferably pH 3 or lower). 【0038】 If the metal to be recovered is a precious metal, a metal ion chelating agent that binds to ions of metals other than the precious metal may be added to the metal dissolution. Such a metal ion chelating agent binds to ions of metals not intended for recovery (e.g., heavy metals) to form a complex. The formation of this complex makes adsorption to yeast less likely, thereby increasing the selectivity of the metal ions to be recovered. Examples of metal ion chelating agents include at least one hydroxycarboxylic acid selected from citric acid, tartaric acid, and gluconic acid, or a salt thereof. Among such metal ion chelating agents, citric acid or a salt thereof is preferred because it is readily available and inexpensive. The amount of metal ion sequestering agent added is preferably the same as or greater than the concentration of the metal ions not intended for recovery, more preferably 1.5 times or more the amount of the metal ions, and particularly preferably 1.7 times or more. There is no particular upper limit to the amount of metal ion sequestering agent added, but a sufficient effect can be obtained with an amount of 2 times or less the amount of the metal ions. 【0039】 The metals that form complexes whose adsorption to yeast is inhibited by such metal ion chelating agents (metals not intended for recovery) are not particularly limited as long as they become cations in solution and form complexes with citric acid, but examples include heavy metals such as iron, nickel, and copper. By adding a metal ion sequestering agent to a metal dissolution solution, the selectivity of the metal ions to be recovered can be increased in a metal dissolution solution where the metal ions to be recovered and other metal ions not to be recovered coexist. 【0040】 The temperature of the mixture of metal dissolution and yeast in the adsorption process can be set, for example, in the range of 1 to 40°C. From the viewpoint of energy costs for temperature control, yeast adsorption performance, and the stability of yeast and metal ions in the liquid, a temperature of 10°C or higher is preferred, 15°C or higher is more preferred, and 20°C or higher is even more preferred. On the other hand, the upper limit of the temperature is preferably 35°C or lower. 【0041】 The time required for the adsorption of metal ions to yeast in the adsorption process (hereinafter referred to as "adsorption time") is set appropriately according to the pH of the mixture, the content and type of metal ions, and, if other metal ions not intended for recovery are present, their content and type. For example, it can be set in the range of 10 minutes to 24 hours. From the viewpoint of allowing sufficient adsorption of metal ions to the yeast, an adsorption time of 30 minutes or more is preferable, while from the viewpoint of efficiency, 12 hours or less is preferable, 8 hours or less is more preferable, and 6 hours or less is even more preferable. When recovering metal ions under conditions where adsorption of metal ions to yeast can occur in a relatively short time, the adsorption time can be set to, for example, 2 hours or less, 1 hour or less, or even 30 minutes or less. Furthermore, if other metal ions that take a long time to adsorb to yeast and are not intended for recovery coexist in this mixture with the metal ions intended for recovery that are adsorbed to yeast in a relatively short time, the selectivity of the metal ions intended for recovery can be increased by adjusting the adsorption time. 【0042】 In the adsorption process, the concentration of metal ions intended for recovery in the metal solution or the mixture of metal solution and yeast, and the concentration of other metal ions not intended for recovery, can be appropriately adjusted according to the yeast cell concentration, for example, 1 × 10 -6 mol / m 3 ~1 × 10 3 mol / m 3 It can be set appropriately within the range, and from the standpoint of improving collection efficiency, 1 x 10 -3 mol / m 3 The above is preferable, 1 × 10 -2 mol / m 3 The above is more preferable, and in terms of recovery rate and / or selection rate, 1 × 10 2 mol / m 3 The following is preferable: 10 mol / m 3 The following is more preferable: 5 mol / m 3 The following are even more preferable. 【0043】 In the adsorption process, the cell concentration (cellular cell concentration) in the mixture of metal dissolution and yeast can be appropriately set according to the concentration of metal ions to be adsorbed by the yeast, for example, 1.0 × 10 6 cells / m 3 ~1.0×10 18 cells / m 3 It can be set to a range of 1.0 × 10 10 cells / m 3 ~1 × 10 16 cells / m 3 Preferably, 1.0 × 10 12 cells / m 3 ~1 × 10 16 cells / m 3 This is preferable. 【0044】 The adsorption process can be a process of continuously supplying the metal dissolution solution and the yeast to a mixing tank, and continuously withdrawing the mixture containing the metal dissolution solution and the yeast from the mixing tank. By making the supply amount and the withdrawal amount the same, the adsorption treatment can be performed continuously. The average residence time in a steady state can be appropriately set according to the conditions related to the adsorption process described above. 【0045】 In the separation step of the embodiment of the present invention, yeast that has adsorbed metal ions is separated from a mixture of metal dissolution and yeast. This separation can be carried out using conventional solid-liquid separation methods, such as centrifugation, filtration, membrane separation, and sedimentation. Two or more of these separation methods may be combined. 【0046】 In the recovery step following the separation step in the embodiment of the present invention, metal ions are recovered from the yeast separated in the separation step. Metal ions adsorbed onto yeast can be recovered by burning the yeast, which allows the metal ions adsorbed onto the yeast to be recovered as a concentrate. If the metal ions are noble metal ions, they can be recovered as a metal mass, which is their reduced form. Furthermore, by treating the yeast with acid, metal ions adsorbed onto the yeast can be removed. As the acidic solution used for this treatment, for example, an acidic solution with a pH of 2 or lower, such as hydrochloric acid, sulfuric acid, or aqua regia, can be used. 【0047】 If solid-liquid separation is performed during the separation process, the separated solid containing yeast can be heat-treated to burn off the yeast. The separated solid containing yeast can be heat-treated after drying to reduce its moisture content, if necessary. For the heat treatment required to burn the yeast, conventional industrial furnaces such as incinerators, calcination furnaces, and combustion furnaces can be used. However, from the standpoint of continuous processing suitable for industrialization, the use of a rotary kiln is preferable. The temperature for burning the yeast can be set as long as it is a temperature at which the yeast can burn, but for example it can be set to 300°C or higher. From the standpoint of burning the yeast more thoroughly, 400°C or higher is preferable, and 500°C or higher is more preferable. On the other hand, from the standpoint of preventing metal oxidation and energy costs, 800°C or lower is preferable, and 750°C or lower is more preferable. The yeast supplied to the furnace may be in a moist state immediately after separation, or it may be in a powdered state after drying. After combustion, the yeast is sublimated or reduced to ash, and the metal ions adsorbed to the yeast can be recovered as a concentrate. If the metal ions are noble metal ions, they become metal lumps in their reduced form, which can then be recovered as metal lumps. 【0048】 As described above, the metal recovery method of the embodiment of the present invention includes an adsorption step, a separation step, and a recovery step, and is performed in this order. Each of these steps may be performed separately, but it is preferable to perform them consecutively from a productivity standpoint. Furthermore, the process including these steps may be repeated multiple times in a batch manner, but it is preferable to perform them consecutively from a productivity standpoint. 【0049】 The process of the metal recovery method according to an embodiment of the present invention will be described below with reference to the drawings. 【0050】 Figures 1 and 2 show block flow diagrams illustrating a metal recovery method according to an embodiment of the present invention. As shown in Figure 1, first, a liquid containing metal ions (metal dissolution solution) is prepared. Next, this metal dissolution solution is mixed with yeast, and the metal ions are adsorbed onto the yeast under predetermined pH and temperature conditions. In this case, if the pH of the metal dissolution is not within the specified range, a pH adjuster (acid or alkali) can be added to the metal dissolution before mixing with yeast or to the mixture after mixing with yeast to adjust it to the specified range. Figure 2(a) shows the case where a pH adjuster is added to the metal dissolution before mixing with yeast. If the pH of the metal dissolution is within the specified range, pH adjustment is not necessary, but if the pH of the mixture changes during the adsorption process and falls outside the specified range, it is preferable to adjust the pH. If the pH of the mixture is not within the specified range during the adsorption process, a pH adjuster (acid or alkali) can be added to the mixture to adjust it to the specified range. 【0051】 If the metal dissolution contains metal ions that are not intended for recovery, a metal ion chelating agent such as citric acid or its salt may be added. When a pH adjuster is added, the metal ion chelating agent may be added before, during, or simultaneously with the pH adjuster. Figure 2(b) shows the case where a pH adjuster and a metal ion chelating agent are added to the metal dissolution before mixing with yeast. 【0052】 After mixing the metal dissolving solution and yeast and allowing a predetermined time to elapse (after the adsorption process is complete), the mixture is subjected to solid-liquid separation to obtain the solid component and the remaining liquid (solid-liquid separation process). Next, the obtained solid is heat-treated to burn off the yeast contained in the solid, and the metal ions adsorbed on the yeast are recovered as a concentrate or metal ingot (recovery step). The solids obtained by solid-liquid separation may be washed as needed before being supplied to the heat treatment furnace. Alternatively, the solids obtained by solid-liquid separation may be dried to reduce their moisture content before being supplied to the heat treatment furnace. Furthermore, when the metal ion recovery process is performed in batches multiple times, or when it is performed continuously using equipment such as described later, the residual liquid obtained by solid-liquid separation can be mixed with the metal dissolution solution before yeast mixing, if necessary. Depending on the separation efficiency of the solid-liquid separation, the residual liquid may be returned to the mixed liquid of the solid-liquid separation process. 【0053】 Figures 3 and 4 show schematic diagrams of an example of equipment configuration that can be used in the metal recovery method of the embodiment of the present invention. 【0054】 The equipment shown in Figure 3 mainly consists of a mixing tank 11 for the adsorption process, a solid-liquid separator 31 for the separation process, and a heat treatment furnace 51 for the recovery process. Between the solid-liquid separator 31 and the heat treatment furnace 51, there is a dryer 41 for drying the solids separated by the solid-liquid separator 31 in order to efficiently burn the yeast in the heat treatment furnace 51. In addition, a dust collector 61 is connected to the exhaust gas outlet side (the supply port side for the separated solids) of the heat treatment furnace 51 to recover powder in the exhaust gas, and the exhaust gas that has passed through the dust collector 61 is blown to the flare stack 64 by a blower 63. 【0055】 The mixing tank 11 is equipped with a stirrer 12 and a temperature control means (not shown) for controlling the temperature inside the tank. The stirrer 12 can mix the yeast so that it is uniformly dispersed in the metal solution. As the temperature control means, for example, a heat transfer medium circulation system can be used, which includes piping arranged inside the tank and a temperature controller that adjusts the temperature of the heat transfer medium for cooling or heating that flows through the piping. 【0056】 A metal dissolving solution is supplied to the mixing tank 11 from the inlet 13 via a control valve 13b. A pH adjusting agent is also supplied to the mixing tank 11 from the inlet 15 via a control valve 15b. Furthermore, as shown in Figure 4, the metal ion chelating agent can also be supplied from the inlet 17 via the control valve 17b. Note that the configuration of the equipment shown in Figure 4 is the same as in Figure 3, except for the part related to the injection of the ion chelating agent. 【0057】 After being stored in the storage section 21, the yeast is transferred to the feeder 23 by air from the air pump 22 via a powder flow rate regulator such as a rotary valve directly below the storage section 21, and then supplied into the mixing tank 11 from the yeast inlet 14 via a powder flow rate regulator such as a rotary valve directly below the feeder 23. As the feeder 23, powder supply devices such as belt type, table type, screw type, vibrating type, and rotary gravity type can be used. 【0058】 The mixed liquid inside the mixing tank 11 can be extracted from the extraction section 16, and the extracted mixed liquid is sent to the solid-liquid separator 31 by the liquid transfer pump 16p. As the solid-liquid separator 31, a sedimentation separator, a centrifugal separator, a membrane separator, a filter, etc., can be used, and two or more of these may be combined. 【0059】 When using filtration methods such as pressure filtration or centrifugal filtration for solid-liquid separation, the particle size of yeast is very small, ranging from 1 μm to 50 μm with an average particle size of approximately 7 μm. Therefore, the aeration rate of the filter cloth should be 30 cc / cm². 2 A minimum of / min is preferable, but since reducing the aeration of the filter cloth will result in a very long filtration time, it is preferable to have a moderate aeration. Also, if the yeast particle size is small and the aeration of the filter cloth is high, leakage may occur from the filter cloth. In that case, it is preferable to supply the leaked slurry to a solid-liquid separator or to a solid-liquid separator of another batch for recycling. This can reduce the loss of yeast during recovery. 【0060】 To reduce leakage from the filter cloth, a filter aid may be added to the mixture. When using a filter aid, it is desirable to use one that is bio-derived, such as cellulose, and can be calcined in a downstream calcination facility. Using a filter aid can also be expected to reduce filtration time. 【0061】 When using filter cloth, it's important to note that yeast tends to pass through the cloth more easily when in contact with the solvent for extended periods. This is thought to be because the yeast becomes more responsive to the solvent or undergoes shearing forces due to prolonged agitation, making it easier for it to pass through the mesh of the filter cloth under centrifugal and pressurized conditions. While this varies depending on the yeast concentration, separation performance can be maintained if the contact time is several hours. Therefore, although it depends on the aeration of the filter cloth, it is preferable to limit the contact time between the yeast and the solvent to several hours. 【0062】 In the case of centrifugal filtration, a centrifugal force of 600G is sufficient to separate yeast that has adsorbed metal ions, and can be set to, for example, 500-700G. In solid-liquid separation, when using solutions with a pH of less than 2, it is desirable to use acid-resistant materials such as Teflon® coating, titanium, or Hastelloy®. When using solutions with a pH of 3 or higher, or pH of 4 or higher, stainless steel (SUS) materials can be used. 【0063】 When using a centrifugal sedimentation machine as a solid-liquid separator, a centrifugal force of 600G or higher is preferable. The preferred processing time varies depending on the centrifugal force, but for 600G, a processing time of 5 to 10 minutes is preferable, and for 1000G or higher, a processing time of a few minutes (for example, 1 to 4 minutes) is preferable. To reduce the water content of the solids after solid-liquid separation, it is preferable to use a centrifugal force of 1000G or higher. On the other hand, depending on the subsequent process (for example, if you want to wash the solids after solid-liquid separation), you may perform multi-stage separation by changing the centrifugal force according to the purpose. This can be done by roughly separating the solvent with a centrifugal force of about 600G, washing the highly fluid solids (cake) with a washing solution while they have a high water content, and then increasing the centrifugal force to perform solid-liquid separation. If the centrifugal force is 1000G or more, solid-liquid separation is sufficient even with a processing time of less than 1 minute. However, if you want to consistently keep yeast leakage into the filtrate within a few percent, it is advisable to set the processing time to several minutes. 【0064】 Furthermore, when using solutions with a pH of less than 2 in solid-liquid separation, it is desirable to use acid-resistant materials such as Teflon® coating, titanium, or Hastelloy®. When using solutions with a pH of 3 or higher, or pH of 4 or higher, SUS (stainless steel) materials can be used. 【0065】 Regarding the removal of solid components (yeast) after solid-liquid separation, it is possible to extrude them by air blowing, regardless of whether centrifugal filtration or centrifugal sedimentation is performed. However, if solid-liquid separation is performed under conditions of low centrifugal force, the viscosity of the solid components may be so high that air blowing becomes difficult, in which case manual scraping is preferable. If the water content of the solid components is reduced by increasing the centrifugal force during solid-liquid separation, the solid components can be automatically scraped off, making it easier to automate the process up to the next heat treatment step. Furthermore, the solid component (yeast) separated from the solid-liquid state has the property of becoming more fluid over time. By utilizing this property to reduce the viscosity of the solid component, it is possible to transport it to the next process using a pump. 【0066】 The residual liquid separated by the solid-liquid separator 31 can be mixed with the metal dissolving solution before being supplied to the mixing tank 11 via the residual liquid recycling line 32 through the control valve 32b. Furthermore, if the residual liquid separated by the solid-liquid separator 31 contains a large amount of yeast, it may be returned to the solid-liquid separator 31 (not shown). 【0067】 The solid components separated by the solid-liquid separator 31 (separated solid components) are dried in the dryer 41 and then transferred to the heat treatment furnace 51. The dryer 41 can be a conventional dryer used for drying powders, such as a ventilated or rotary dryer. The separated solids may be supplied to the heat treatment furnace 51 without drying them in the dryer 41, and both drying and heat treatment (combustion) of the separated solids may be performed in the heat treatment furnace 51. However, it is preferable to dry the separated solids beforehand to improve the efficiency of the heat treatment. In particular, if the acidity of the separated solids is high (for example, pH 5 or lower), it is preferable to perform a drying treatment beforehand. By performing a drying treatment, acidic components contained in the separated solids can be removed, thereby preventing corrosion of the heat treatment furnace 51 by acid. Furthermore, when the acidity of the separated solids is high (for example, pH 5 or lower), and the separated solids are supplied to the heat treatment furnace 51 without drying, it is preferable to wash the separated solids beforehand to lower their acidity, preferably to pH 5.2 to 7, and more preferably to pH 6 to 7. 【0068】 As the heat treatment furnace 51, a general-purpose incinerator or industrial furnace such as an electric furnace can be used, and there are no particular restrictions as long as it can burn yeast, but a rotary kiln is preferred. With a rotary kiln, drying of the separated solids, burning of yeast, and recovery of metal can be carried out continuously. 【0069】 The separated solids supplied to the heat treatment furnace 51 (e.g., a rotary kiln) are gradually fed in while slowly rotating. Meanwhile, the separated solids are gradually dried by combustion using air and fuel supplied from the opposite side of the solid supply, and then the yeast in the solids is burned. As a result, the yeast is sublimated or incinerated, and the metal ions adsorbed on the yeast are recovered as a concentrate. If the metal ions are noble metal ions, they become their reduced metal form and are recovered in the form of metal ingots by cooling. 【0070】 The exhaust gas from the heat treatment furnace 51 is blown to the flare stack 64 by a blower 63 via a dust collector 61. The powder recovered by the dust collector 61 is mixed with the separated solids before being supplied to the heat treatment furnace 51 via a conveyor line 62 such as a belt conveyor. Since this recovered powder contains yeast that has adsorbed metal ions, mixing it with the separated solids can increase the metal recovery rate. [Examples] 【0071】 The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. 【0072】 (Example 1) First, an aqueous solution containing Dy ions was prepared as a metal dissolving solution as follows: DyCl3 was dissolved in pure water, and hydrochloric acid was added to adjust the pH to 4.5-5, resulting in a concentration of 1.0 mol / m³. 3 A DyCl3 aqueous solution was prepared. Next, to the obtained DyCl3 aqueous solution, dried baker's yeast (manufactured by Oriental Yeast Co., Ltd., product name: Dry Yeast 500G) was added to a cell concentration of 5.0 × 10⁻⁶ 14 cells / m 3 A test solution was prepared by adding (18 g / L of dried baker's yeast), and the resulting test solution was shaken and stirred in an incubator (34°C). Cell concentration was measured by hematometer. Next, a portion of the test solution was taken at predetermined time intervals and filtered through a filtration filter with a pore size of 0.2 μm. After recovering Dy ions as described above, the Dy ion concentration (Dy(III) concentration) in the obtained filtrate (liquid phase) was measured by ICP (Inductively Coupled Plasma) emission spectroscopy. The results are shown in Figure 5. As is clear from Figure 5, the Dy(III) concentration in the liquid phase has decreased, indicating that Dy ions have been adsorbed onto the solid content (recovered baker's yeast) obtained by filtration. 【0073】 (Example 2) Cell concentration 2.5 × 10 14 cells / m 3 The Dy ion recovery process using yeast was carried out in the same manner as in Example 1, except that the concentration was changed to (9 g / L of dried baker's yeast). The Dy ion concentration in the filtrate was measured in the same manner as in Example 1, and the results are shown in Figure 5. 【0074】 (Example 3) Cell concentration 1.0 × 10 14 cells / m 3The Dy ion recovery treatment using yeast was carried out in the same manner as in Example 1, except that the concentration was changed to (dried baker's yeast 3.6 g / L). The Dy ion concentration in the filtrate was measured in the same manner as in Example 1, and the obtained results are shown in Figure 5. 【0075】 (Comparative Example 1) A test solution was prepared in the same manner as in Example 1, except that dried baker's yeast was not added. The obtained test solution was then treated in the same manner as in Example 1, and the Dy ion concentration was measured. The results are shown in Figure 5. 【0076】 (Example 4) First, an aqueous solution containing Dy ions was prepared as a metal dissolving solution as follows: DyCl3 was dissolved in pure water, hydrochloric acid was added to adjust the pH to 3.0, and a concentration of 1.0 mol / m³ was obtained. 3 A DyCl3 aqueous solution was prepared. Next, to the obtained DyCl3 aqueous solution, dried baker's yeast (Oriental Yeast Co., Ltd., product name: Dry Yeast 500G) was added to a cell concentration of 4.4 × 10⁻⁶. 14 cells / m 3 A test solution was prepared by adding 16 g / L (1.6 wt%) of dried baker's yeast, and the resulting test solution was shaken and stirred in an incubator (34°C). Cell concentration was measured using a hematometer. Next, after a predetermined time (10 minutes), a portion of the test solution was taken and filtered through a filtration filter with a pore size of 0.2 μm. After the Dy ion recovery process described above, the Dy ion concentration in the obtained filtrate was measured by ICP (Inductively Coupled Plasma) emission spectroscopy. Based on the measurement results, the Dy recovery rate (the ratio (%) of the amount of Dy ions adsorbed on the yeast to the amount of Dy ions in the metal solution before yeast addition) was determined. The results are shown in Figure 6. The recovery rate (adsorption rate) was calculated according to the following formula. Recovery rate (%) = (Dy ion concentration in metal dissolution before yeast addition - Dy ion concentration in filtrate) / Dy ion concentration in metal dissolution before yeast addition × 100 【0077】 (Example 5) The Dy ion recovery treatment using yeast was carried out in the same manner as in Example 4, except that the pH of the DyCl3 aqueous solution was set to 4.0. The Dy recovery rate based on the measurement results of the Dy ion concentration in the filtrate is shown in Figure 6. 【0078】 (Example 6) The Dy ion recovery treatment using yeast was carried out in the same manner as in Example 4, except that the pH of the DyCl3 aqueous solution was set to 5.0. The Dy recovery rate based on the measurement results of the Dy ion concentration in the filtrate is shown in Figure 6. 【0079】 (Example 7) The Dy ion recovery treatment using yeast was carried out in the same manner as in Example 4, except that the pH of the DyCl3 aqueous solution was set to 2.5. The Dy recovery rate based on the measurement results of the Dy ion concentration in the filtrate is shown in Figure 6. 【0080】 (Example 8) The Dy ion recovery treatment using yeast was carried out in the same manner as in Example 4, except that the pH of the DyCl3 aqueous solution was set to 2.7. The Dy recovery rate based on the measurement results of the Dy ion concentration in the filtrate is shown in Figure 6. 【0081】 (Example 9) First, as a metal dissolving solution, an aqua regia leachate from electrical and electronic waste (E-waste) was prepared, and sodium hydroxide solution was added to adjust the pH to 3.5. This metal dissolving solution (aqua regia leachate after pH adjustment) contained Au ions, with a concentration of 183 ppm (mg / L). Next, dried baker's yeast (manufactured by Oriental Yeast Co., Ltd., product name: Dry Yeast 500G) is added to a cell concentration of 5.0 × 10 14 cells / m 3 The test solution was prepared by adding (18 g / L of dried baker's yeast) and then shaken and stirred in an incubator (34°C). Next, a portion of the test solution was taken at predetermined time intervals and filtered through a filtration filter with a pore size of 0.2 μm. After recovering Au ions as described above, the Au ion concentration in the obtained filtrate was measured by ICP (Inductively Coupled Plasma) emission spectroscopy, and the Au recovery rate (the ratio (%) of the amount of Au ions adsorbed on the yeast to the amount of Au ions in the metal dissolution solution before yeast addition) was determined based on the measurement results. This recovery rate (adsorption rate) was calculated according to the following formula. Recovery rate (%) = (Au ion concentration in metal dissolution before yeast addition - Au ion concentration in filtrate) / Au ion concentration in metal dissolution before yeast addition × 100 The Au recovery rate (adsorption rate) of the test solution to which yeast was added was approximately 64% at 10 minutes, 1 hour, 2 hours, and 6 hours after the start of shaking and stirring. 【0082】 (Example 10) Except for not adjusting the pH with an aqueous sodium hydroxide solution, a test solution (pH<0) was prepared in the same manner as in Example 9, shaken and stirred, filtered, and the Au ion concentration in the filtrate was measured. The Au recovery rate (adsorption rate) 1 hour after the start of immersion stirring was 34%. 【0083】 (Example 11) First, as a metal dissolving solution, an aqua regia leachate from electrical and electronic waste (E-waste) was prepared, and sodium hydroxide solution was added to adjust the pH to 3.5. This metal dissolving solution (aqua regia leachate after pH adjustment) contains Au ions, Cu ions, Fe ions, and Ni ions, and the content of each (mg / 1L) is shown in Table 1. Next, dried baker's yeast (manufactured by Oriental Yeast Co., Ltd., product name: Dry Yeast 500G) is added to a cell concentration of 5.0 × 10 14 cells / m 3 The test solution was prepared by adding (18g / L of dried baker's yeast) and then shaken at a temperature of 34°C. Next, after one hour, the treatment solution containing the yeast was centrifuged to recover the yeast, which was then washed with water. Subsequently, the yeast was treated with aqua regia to elute the metals in the yeast cells, and the content (mg / L) of each metal ion in the liquid phase was measured by ICP (Inductively Coupled Plasma) emission spectroscopy. Based on these measurement results, the amount of metal adsorbed to the yeast (mg / 18g of dried baker's yeast) was determined, and the recovery rate was obtained. The results are shown in Table 1. 【0084】 (Example 12) Except for adding sodium citrate to the aqua regia leachate so that the concentration of sodium citrate in the pH-adjusted solution was 0.5 M, the adsorption treatment of each metal ion onto yeast, yeast recovery, and acid treatment were carried out in the same manner as in Example 11, and the content of each metal ion in the treated solution and baker's yeast was measured. The results are shown in Table 1. It can be seen that by adding sodium citrate, the Au recovery rate was 57%, which is about the same as the Au recovery rate of 58% in Example 11 without sodium citrate, but the recovery rates of Cu and Fe were lower, and the selectivity for Au recovery was increased. 【0085】 [Table 1] The metal content (mg / L) in the examples in the table indicates the amount adsorbed on 18g of dried yeast. The percentages (%) in parentheses in the table's examples indicate the metal recovery rate. 【0086】 (Example 13) The Nd ion recovery treatment using yeast was carried out in the same manner as in Example 1, except that an aqueous NdCl3 solution prepared as follows was used instead of an aqueous DyCl3 solution as the metal dissolving solution. To prepare an aqueous solution of NdCl3, first dissolve NdCl3 in pure water, then add hydrochloric acid to adjust the pH to 5, and then make a solution of 1.0 mol / m³. 3 An aqueous solution of NdCl3 was obtained. Using this NdCl3 aqueous solution, Nd ions were recovered by yeast in the same manner as in Example 1, and the Nd ion concentration in the filtrate of the test solution collected at predetermined time intervals was measured. The results obtained are shown in Figure 7. Figure 7 also shows the measurement results of the Dy ion concentration in Example 1. It can be seen that Nd ions, like Dy ions, are adsorbed by baker's yeast. 【0087】 (Example 14) The Nd ion recovery treatment using yeast was carried out in the same manner as in Example 4, except that an aqueous NdCl3 solution prepared as follows was used instead of an aqueous DyCl3 solution as the metal dissolving solution. To prepare NdCl3 aqueous solutions, first dissolve NdCl3 in pure water, then add hydrochloric acid to adjust the pH, and prepare 1.0 mol / m³ solutions at pH 2.5, pH 2.7, pH 3.0, pH 4.0, and pH 5.0. 3 An aqueous solution of NdCl3 was obtained. Using the obtained NdCl3 aqueous solution, Nd ions were recovered by yeast in the same manner as in Example 4. The Nd recovery rates based on the measurement of the Nd ion concentration in the filtrate are shown in Table 2. The measurement results of the Dy recovery rates for Examples 4 to 8 are also shown in Table 2. The recovery rate (adsorption rate) of Nd ions is about 10% at pH 2.5, similar to that of Dy ions, but it improves as the pH increases, and a high recovery rate of over 80% can be obtained at pH 4 to 5. It can also be seen that a relatively high recovery rate (adsorption rate) of Nd ions can be obtained even at pH 3. 【0088】 [Table 2] 【0089】 (Example 15) First, a hydrochloric acid leachate of electrical and electronic waste (E-waste) was prepared as the metal dissolving solution, and sodium hydroxide solution was added to adjust the pH to 1.0. This metal dissolving solution (hydrochloric acid leachate after pH adjustment) contained Au ions, Cu ions, Fe ions, and Ni ions, with concentrations of 44.8 ppm (mg / L), 156 ppm, 771 ppm, and 544 ppm, respectively. Next, the metal dissolution solution is added to a 1L mixing tank, and then dried baker's yeast (manufactured by Oriental Yeast Co., Ltd., product name: Dry Yeast 500G) is added to a cell concentration of 3.3 × 10⁻⁶.14 cells / m 3 Add 12g / L of dried baker's yeast, and stir the mixture of baker's yeast and metal solution for 30 minutes until it reaches adsorption equilibrium. Next, the metal dissolving solution was quantitatively supplied to the mixture in the mixing tank at a rate of 16.7 mL / min (1 L / h), and dried baker's yeast at a rate of 0.2 g / min. Simultaneously, the mixture was quantitatively withdrawn from the reaction tank at a rate of 16.7 mL / min (1 L / h), and the process was carried out continuously by adjusting the average residence time of the mixture to 1 hour. 【0090】 In the continuous adsorption process described above, the following procedure was performed to confirm that Au ions could be continuously recovered. A portion of the mixture was taken from the mixing tank at predetermined time intervals and filtered through a 0.2 μm pore filter. The metal ion concentration in the resulting filtrate was measured by ICP (Inductively Coupled Plasma) emission spectroscopy. Based on the obtained measurement results, the Au recovery rate (the ratio (%) of the amount of Au ions adsorbed on the yeast to the amount of Au ions in the metal solution before yeast addition) was determined. The recovery rates (Cu recovery rate, Fe recovery rate, Ni recovery rate) were similarly determined for other metal ions. This recovery rate (adsorption rate) was calculated according to the following formula. Recovery rate (%) = (Concentration of metal ions in the metal solution before yeast addition - Concentration of metal ions in the filtrate) / Concentration of metal ions in the metal solution before yeast addition × 100 【0091】 Table 3 shows the concentrations of each metal ion (Au concentration, Cu concentration, Fe concentration, and Ni concentration) and the recovery rate (adsorption rate) in the filtrate after a predetermined time has elapsed from the start of quantitative supply. Note that "Time" in the table indicates the time (min) from the start of quantitative supply. The numerical values ​​for metal concentration in the leftmost column of the table indicate the concentration (mg / L) of each metal ion in the metal dissolution before yeast addition. As shown in Table 3, the Au recovery rate (adsorption rate) remained almost constant throughout the entire time period. When the average residence time of the mixed solution was 1 hour, the steady-state Au recovery rate was approximately 96%. The Au recovery rate at this time was 0.043 kg-Au / h / m 3 This is the result. Furthermore, the decrease in metal ion concentration was small for Cu ions, Fe ions, and Ni ions, indicating that the adsorption treatment in this embodiment has a high selectivity for Au ions over these heavy metal ions. 【0092】 [Table 3] [Explanation of symbols] 【0093】 11 Mixing tank 12. Agitator 13 Metal solution inlet 13b Metal dissolving solution injection control valve 14 Yeast inlet 15 pH adjuster inlet 15b pH adjuster injection control valve 16 Mixture extraction section 16p Mixed Liquid Transfer Pump 17 Ion sequestering agent inlet 17b Ion sequestering agent injection control valve 21 Storage section 22 Air Pumps 23 Feeder 31 Solid-liquid separator 32 Residual Liquid Recycling Line 32b Residual liquid control valve 41 Dryer 51 Heat treatment furnace 61 Dust collector 62. Conveyor line for recovered powder (belt conveyor) 63 Blower 64 Flare Stack FIC:Flow rate indicating controller MCC: Motor Control Center M: Prime Engine

Claims

[Claim 1] An adsorption step is performed in which a liquid containing metal ions is mixed with yeast, and the metal ions are adsorbed onto the yeast in the resulting mixture. A separation step is performed to separate the yeast from the mixture obtained in the adsorption step, A method for recovering metals, comprising a recovery step of recovering the metal ions from the yeast separated in the separation step, In the adsorption step, the metal ions adsorbed onto the yeast are rare earth ions and / or noble metal ions. A method for recovering metal, wherein the adsorption step is a step of continuously supplying the liquid and the yeast to a mixing tank and continuously withdrawing the mixture containing the liquid and the yeast from the mixing tank. [Claim 2] The aforementioned metal ion is a rare earth ion, The method for recovering a metal according to claim 1, wherein the pH of the mixed solution in the adsorption step is 2.5 or more and less than 7. [Claim 3] The aforementioned metal ion is a noble metal ion, The method for recovering a metal according to claim 1, wherein the pH of the mixed solution in the adsorption step is less than 4. [Claim 4] The method for recovering a metal according to claim 1, wherein the metal ion includes an Nd ion or a Dy ion. [Claim 5] The method for recovering a metal according to claim 1, wherein the metal ions include gold ions. [Claim 6] The method for recovering metals according to any one of claims 1 to 5, wherein the liquid before mixing with yeast further contains ions of metals other than rare earths or precious metals. [Claim 7] The method for recovering a metal according to claim 6, wherein the metal other than rare earth elements or precious metals is at least one selected from iron, copper, nickel, aluminum, manganese, magnesium, and zinc. [Claim 8] The method for recovering metal according to claim 6, wherein the metal ion is a noble metal ion, and in the adsorption step, a metal ion chelating agent that binds to metal ions other than noble metals is added to the liquid or the mixture before mixing in the yeast. [Claim 9] The method for recovering metal according to claim 8, wherein the metal ion chelating agent is citric acid or a salt thereof. [Claim 10] The method for recovering metal according to any one of claims 1 to 5, wherein the yeast is baker's yeast. [Claim 11] The separation step is a step of obtaining separated solids by performing solid-liquid separation on the mixed liquid obtained in the adsorption step, The method for recovering metals according to claim 1, wherein the recovery step is a step of treating the separated solids obtained in the separation step with acid to recover the metal ions adsorbed on the yeast. [Claim 12] The separation step is a step of obtaining separated solids by performing solid-liquid separation on the mixed liquid obtained in the adsorption step, The method for recovering metals according to claim 1, wherein the recovery step is a step of heat-treating the separated solids obtained in the separation step to burn the yeast and recover the metal ions adsorbed on the yeast as a concentrate. [Claim 13] The method for recovering metal according to claim 12, wherein in the recovery step, the heat treatment of the separated solids is performed by firing in an industrial furnace. [Claim 14] The method for recovering metal according to claim 12, comprising recovering powder from the exhaust gas of the heat treatment process and mixing the recovered powder with the separated solids before the heat treatment process. [Claim 15] The method for recovering metal according to any one of claims 11 to 14, wherein the solid-liquid separation is carried out by at least one selected from centrifugal separation, filtration, membrane separation, and sedimentation separation. [Claim 16] A method for recovering metal according to any one of claims 11 to 14, further comprising a drying step to reduce the moisture content of the separated solids. [Claim 17] A method for recovering metal according to any one of claims 11 to 14, wherein the separated liquid obtained in the solid-liquid separation of the separation step is mixed with the liquid containing metal ions before the yeast is mixed in. [Claim 18] An adsorption step is performed in which a liquid containing metal ions is mixed with yeast, and the metal ions are adsorbed onto the yeast in the resulting mixture. A separation step is performed to separate the yeast from the mixture obtained in the adsorption step, A method for recovering metals, comprising a recovery step of recovering the metal ions from the yeast separated in the separation step, In the aforementioned adsorption step, the metal ions adsorbed onto the yeast are rare earth ions. A method for recovering metal, wherein the pH of the mixed solution in the adsorption step is 2.5 or higher and less than 7. [Claim 19] An adsorption step is performed in which a liquid containing metal ions is mixed with yeast, and the metal ions are adsorbed onto the yeast in the resulting mixture. A separation step is performed to separate the yeast from the mixture obtained in the adsorption step, A method for recovering metals, comprising a recovery step of recovering the metal ions from the yeast separated in the separation step, In the aforementioned adsorption step, the metal ions adsorbed onto the yeast are noble metal ions. The liquid before mixing in the yeast further contains ions of metals other than precious metals, A method for recovering metals, comprising adding a metal ion chelating agent that binds to metal ions other than precious metals to the liquid or mixture before mixing in yeast in the adsorption step. [Claim 20] An adsorption step is performed in which a liquid containing metal ions is mixed with yeast, and the metal ions are adsorbed onto the yeast in the resulting mixture. A separation step is performed to separate the yeast from the mixture obtained in the adsorption step, A method for recovering metals, comprising a recovery step of recovering the metal ions from the yeast separated in the separation step, In the adsorption step, the metal ions adsorbed onto the yeast are rare earth ions and / or noble metal ions. The separation step is a step of obtaining separated solids by performing solid-liquid separation on the mixed liquid obtained in the adsorption step, A method for recovering metals, wherein the recovery step is a step of treating the separated solids obtained in the separation step with acid to recover the metal ions adsorbed on the yeast. [Claim 21] An adsorption step is performed in which a liquid containing metal ions is mixed with yeast, and the metal ions are adsorbed onto the yeast in the resulting mixture. A separation step is performed to separate the yeast from the mixture obtained in the adsorption step, A method for recovering metals, comprising a recovery step of recovering the metal ions from the yeast separated in the separation step, In the adsorption step, the metal ions adsorbed onto the yeast are rare earth ions and / or noble metal ions. The separation step is a step of obtaining separated solids by performing solid-liquid separation on the mixed liquid obtained in the adsorption step, A method for recovering metals, comprising mixing the separated liquid obtained in the solid-liquid separation step with the liquid containing metal ions before mixing with the yeast. [Claim 22] An adsorption step is performed in which a liquid containing metal ions is mixed with yeast, and the metal ions are adsorbed onto the yeast in the resulting mixture. A separation step is performed to separate the yeast from the mixture obtained in the adsorption step, A method for recovering metals, comprising a recovery step of recovering the metal ions from the yeast separated in the separation step, In the adsorption step, the metal ions adsorbed onto the yeast are rare earth ions and / or noble metal ions. The separation step is a step of obtaining separated solids by performing solid-liquid separation on the mixed liquid obtained in the adsorption step, The recovery step is a step of heat-treating the separated solid obtained in the separation step to burn the yeast and recover the metal ions adsorbed on the yeast as a concentrate. A method for recovering metal, comprising recovering powder from the exhaust gas of the heat treatment process and mixing the recovered powder with the separated solids before the heat treatment process.

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