JP2015052164A - Metal recovery method and metal recovery device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recover metal easily and continuously in high efficiency from a metal ion-containing solution.SOLUTION: A method for recovering a metal from metal ion-containing solution, comprising the following steps (1) and (2); the method for recovering metal, further comprising the following step (3); the method for recovering metal, comprising making bivalent iron ions act in the step (2); the method for recovering metal wherein metal formed by reducing the metal ion is included in the step (1); and a metal recovering device: (1) a reduction step of making a water-soluble reductant act on a metal ion-containing solution to reduce the metal ion to obtain metal fine particles; (2) a concentration step of concentrating a solution containing the metal fine particles obtained by the step (1) by using a filtration membrane to obtain a concentrated liquid; and (3) a return step of returning the concentrated liquid obtained by the step (2) to the step (1).

Description

  The present invention relates to a metal recovery method and a metal recovery apparatus.

2. Description of the Related Art Conventionally, metals are widely recovered from solutions containing metals such as industrial wastewater and leachable noble liquids for the purpose of reusing resources in addition to the purpose of satisfying legal water quality standards.
In particular, metal recovery from a metal-containing solution containing a low concentration metal to be recovered includes a method using an ion-exchange resin, activated carbon or the like, and (i) a method using an adsorbent having a metal chelating ability (for example, Patent Document 1). 2), (ii) a method using a porous carrier carrying a reducing agent (for example, Patent Document 3), (iii) a method using a microorganism (for example, Patent Documents 4 to 6), (iv) hydrogen A method (for example, Patent Document 7) in which metal fine particles are obtained by reduction with an occlusion alloy is known.

However, in addition to the method using ion exchange resin, activated carbon, etc., in the method described in (i) and the method described in (ii), these adsorption carriers are expensive or the manufacturing process of the carrier is complicated, There is a problem that the metal recovery process from the support is complicated.
In the method described in (iii), the process of preparing a microorganism capable of capturing a metal by culturing or the like is complicated, and the metal possessed by the microorganism itself is collected when the target metal is recovered from the microorganism. There is a problem that separation from minutes is necessary.
Furthermore, the method described in (iv) has a problem that the hydrogen storage alloy is expensive, and that the target metal needs to be separated from the hydrogen storage alloy when the target metal is recovered.

JP 2004-83926 A JP 2008-95072 A JP-A-7-185568 JP 2011-241475 A JP-T 62-500931 gazette JP 2007-113116 A JP 2005-281830 A

As described above, various methods have been studied as methods for recovering metals from solutions containing metal resources useful in the industry. These methods include steps for preparing carriers or microorganisms for capturing metals, carriers or microorganisms. The metal recovery process was complicated and was not always economically satisfactory.
An object of the present invention is to solve such a conventional problem.

  The present invention provides a metal recovery method and a metal recovery apparatus that can recover metal from a metal-containing solution simply and with high recovery efficiency.

That is, this invention has the following aspect.
[1] A method for recovering a metal from a solution containing metal ions, comprising the following steps (1) and (2).
(1) A reduction step in which a water-soluble reducing agent is allowed to act on a metal ion-containing solution to reduce metal ions to form metal fine particles;
(2) A concentration step of concentrating the solution containing the metal fine particles obtained in the step (1) with a filtration membrane to obtain a concentrated solution;
[2] The metal recovery method according to the aspect [1], further including the following step (3).
(3) A returning step of returning the concentrate obtained in the step (2) to the step (1);
[3] The metal recovery method according to the aspect [1] or [2], wherein in the step (1), divalent iron ions are further allowed to act.
[4] The metal recovery method according to any one of the aspects [1] to [3], wherein in the step (1), a metal obtained by reducing the metal ion is previously contained.
[5] Any one of the above aspects [1] to [4], wherein the metal ion is an ion of one or more elements selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os. The metal recovery method according to item.
[6] The metal recovery method according to any one of [1] to [5], wherein the water-soluble reducing agent is an aliphatic aldehyde having 1 to 5 carbon atoms.
[7] The metal recovery method according to the above aspect [6], wherein the aliphatic aldehyde having 1 to 5 carbon atoms is formic acid and / or a salt thereof.
[8] A metal recovery apparatus including the following (a) and (b).
(A) A storage unit for storing a liquid containing metal fine particles obtained by allowing a water-soluble reducing agent to act on a solution containing metal ions;
(B) A concentration unit that concentrates the liquid containing the metal fine particles in the step (a) with a filtration membrane;
[9] The metal recovery apparatus according to the aspect [8], further including the following step (c).
(C) A return unit that returns the concentrate obtained in the step (b) to the step (a);

  By using the metal recovery method and / or metal recovery apparatus of the present invention, metal fine particles can be easily recovered from a metal ion-containing solution with high efficiency.

It is the schematic block diagram which showed an example of the metal collection | recovery apparatus of this invention.

<Metal recovery method>
The present invention is a method for recovering a metal from a solution containing metal ions, which includes the following steps (1) and (2).
(1) A reduction step in which a water-soluble reducing agent is allowed to act on a metal ion-containing solution to reduce metal ions into metal fine particles;
(2) A concentration step of concentrating the solution containing the metal fine particles obtained in the step (1) with a filtration membrane to obtain a concentrated solution;
Among these, when the metal formed by reducing the metal ion catalyzes the reduction reaction, it is preferable that the following step (3) is further included.
(3) A returning step of returning the concentrate obtained in the step (2) to the step (1);
Moreover, in the said process (1), it is preferable to make a bivalent iron ion act from the point which accelerates | stimulates a reductive reaction more.
In the step (1), it is preferable to coexist a metal obtained by reducing the metal ion from the viewpoint of further promoting the reduction reaction.
The metal ion is not particularly limited, but is preferably an ion of one or more elements selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os from the viewpoint of high reducibility. .

(Water-soluble reducing agent)
The reducing agent in the present invention is a water-soluble reducing agent. Here, the term “water-soluble” means that 100 mg / L or more dissolves in normal temperature / neutral water.
The reducing agent is not particularly limited as long as it is water-soluble and capable of reducing the target metal ion. For example, hypophosphorous acids, phosphorous acids, hydrazines, hydroquinones, carbon number 1-5 aliphatic aldehydes and the like.

Examples of the hypophosphorous acid include hypophosphorous acid, sodium hypophosphite (monohydrate), ammonium hypophosphite and the like.
Specific examples of phosphorous acids include phosphorous acid, sodium hydrogen phosphite, and dipotassium phosphite.
Examples of the hydrazines include hydrazine; hydrazine salts such as hydrazine sulfate and hydrazine hydrochloride; hydrazine derivatives such as pyrazoles, triazoles and hydrazides. Among these, examples of pyrazoles include pyrazole derivatives such as 3,5-dimethylpyrazole and 3-methyl-5-pyrazolone in addition to pyrazole. As triazoles, 4-amino-1,2,4-triazole, 1,2,3-triazole and the like can be used. Examples of hydrazides include adipic hydrazide and maleic hydrazide.
Examples of hydroquinones include hydroquinone and its salts, catechol and its salts, resorcinol and its salts, naphthohydroquinone and its salts, anthrahydroquinone and its salts, and substituted isomers thereof.
Examples of the aliphatic aldehyde having 1 to 5 carbon atoms include formic acid and / or a salt thereof, formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, isobutyraldehyde, valeraldehyde, and isovaleraldehyde.
These reducing agents may be used alone or in combination of two or more.
In particular, an aliphatic aldehyde having 1 to 5 carbon atoms is preferable, an aliphatic aldehyde having 1 to 3 carbon atoms is more preferable, and an aqueous solution of formic acid and / or a salt thereof is more preferable because it is inexpensive and excellent in biodegradability.

<Metal recovery device>
The metal recovery apparatus of the present invention includes the following (a) and (b).
(A) A storage unit for storing a liquid containing metal fine particles obtained by allowing a water-soluble reducing agent to act on a solution containing metal ions;
(B) A concentration unit that concentrates the liquid containing the metal fine particles in the step (a) with a filtration membrane;

When the metal obtained by reducing the metal ions catalyzes the reduction reaction, it is preferable that the metal recovery apparatus of the present invention further includes the following step (c) from the viewpoint of further promoting the reduction reaction.
(C) A return unit that returns the concentrate obtained in the step (b) to the step (a);

The configuration will be described.
<(A) Reservoir>
(A) Storage part: The reaction liquid storage tank 10 is supplied with the metal ion-containing solution W ₀ from the metal ion-containing solution storage tank 20 through the pipe 50, and from the reducing agent storage tank 24 through the pipe 54 with a water-soluble reducing agent (hereinafter referred to as a water-soluble reducing agent). , Also referred to as reducing agent B). The supplied metal ion-containing solution W ₀ and the reducing agent B are stirred and mixed by the stirring blade 10a, and the metal ions in the metal ion-containing solution W ₀ are reduced to generate metal fine particles. The material of the reaction liquid storage tank 10 may be any material as long as it is not easily corroded by the metal-containing solution W ₀ and the reducing agent B and does not adversely affect the action of the reducing agent.

<(B) Concentration part>
(B) concentrating unit: a membrane module 14 having a filtration membrane, the metal fine particle-containing solution W ₁ is supplied through the pipe 56 from the reaction liquid reservoir 10. The secondary side (filtered water side) 14b of the filtration membrane in the membrane module 14 is connected to the filtration pump 48 through the pipe 46, and the filtration pump 48 operates to contain metal fine particles from the primary side 14a of the filtration membrane. Concentrated liquid W ₂ is obtained from filtered water W ₃ from the secondary side 14b.

The filtration membrane is not particularly limited as long as it can capture metal fine particles, and a known membrane such as a hollow fiber membrane, a flat membrane, a tubular membrane, or a monolith type membrane can be used. Among these, a hollow fiber membrane is preferable as the filtration membrane because of its high volume filling rate.
The material of the filtration membrane, as long as it is not corroded by the metal fine particle-containing solution W _1, not particularly limited, inorganic membranes such as ceramics, cellulose, cellulose mixed ester, polyolefin, polysulfone, polyvinylidene fluoride (PVDF), poly An organic film such as tetrafluoroethylene (PTFE) can be used. Among these, ceramic, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE) are preferable from the viewpoint of resistance to chemical resistance and pH change.

The average pore diameter of the micropores formed in the filtration membrane is not particularly limited as long as the metal fine particles can be captured, but is preferably 0.01 to 1.0 μm, and more preferably 0.05 to 0.4 μm.
Here, if the average pore diameter of the micropores is not less than the lower limit value, the pressure required for membrane filtration can be easily reduced and the concentration efficiency of the fine particles can be easily increased.
Moreover, if the average pore diameter of the micropores is equal to or less than the upper limit value, it is easy to suppress leakage of metal fine particles to the secondary side of the filtration membrane.

<(C) Return part>
(C) Return part: In the membrane module 14, the concentrated liquid W ₂ containing metal fine particles obtained from the primary side 14 a of the filtration membrane is returned to the reaction liquid storage tank 10 through the pipe 58. When the metal fine particles catalyze the reduction of the metal ions by the reducing agent, the reaction efficiency can be increased by increasing the concentration of the metal fine particles in the reaction liquid storage tank 10.

The present invention may include the following step (a ′) before the step (a).
<((A ′) supply section>
(A ′) Supply unit: The metal-containing solution storage tank 20 is a storage tank that temporarily stores the metal ion-containing solution W ₀ . Metal-containing solution storage tank 20, as long as it can store the metal-containing solution W _0, not particularly limited.
The reducing agent reservoir 24 is means for temporarily storing the reducing agent B necessary for the reduction of the metal ions contained in the metal-containing solution W ₀ metal particles. The reducing agent storage tank 24 is not particularly limited as long as it can store the reducing agent B.
The metal-containing solution storage tank 20 and the reaction liquid storage tank 10 are connected by a pipe 50, and the reducing agent storage tank 24 and the reaction liquid storage tank 10 are connected by a pipe 54.

In addition to the above (a) to (c) (or (a ′) to (c)), the metal recovery apparatus 1 includes a recovery unit 16: metal fine particles that are sent from the reaction liquid storage tank 10 through the pipe 44. portion for recovering the concentrated solution W _1, and, the filtered water storage tank 18: a portion for storing filtered water W ₃ having passed through the filtration membrane of the membrane module 14, may be included.
Recovery unit 16 is not particularly limited as long as it can collect the fine metal particles-containing solution W _1.

The filtered water storage tank 18 is not particularly limited as long as the filtered water W ₃ can be stored.
The filtered water storage tank 18 may have a pH adjusting unit that adjusts the pH of the filtered water W ₃ to be suitable for discharge to a river or the like as necessary.
The pH adjusting means may be any means as long as the pH of the filtered water W ₃ can be adjusted to a desired pH, and examples thereof include a pH meter, an acid addition device, and an alkali addition device.

In the metal recovery apparatus 1, the metal ion-containing solution W ₀ is supplied from the metal-containing solution storage tank 20, and the reducing agent B is supplied from the reducing agent storage tank 24 to the reaction liquid storage tank 10. At this time, it is preferable that a metal obtained by reducing the metal ions coexist in the reaction liquid storage tank 10 in terms of improving the reduction reaction efficiency.
In addition, a part of the metal fine particle-containing solution W ₁ obtained by reducing the metal ions contained in the metal ion-containing solution W ₀ with the reducing agent in the reaction liquid storage tank 10 is filtered by the filtration membrane of the membrane module 14, The solution containing the metal fine particles is concentrated, and the metal fine particle-containing concentrated solution W ₂ (concentrated liquid) is returned to the reaction liquid storage tank 10, whereby the metal of the metal fine particle-containing solution W _{1 in} the reaction liquid storage tank 10. The fine particle concentration increases. The metal fine particle-containing solution W _{1 that} has risen to a desired concentration can be recovered by the recovery unit 16.
The filtered water W ₃ filtered by the filtration membrane is discharged in the filtered water storage tank 18 with the pH adjusted as necessary.

  In the metal recovery apparatus of the present invention described above, a part of the solution containing metal fine particles obtained by reducing metal ions in a metal ion-containing solution with a reducing agent is transferred to a concentration section, and the fine particles are filtered. Filtration through a membrane and concentration to obtain a concentrated solution containing the fine particles. Therefore, metal can be continuously recovered from the metal ion-containing solution with high efficiency.

The metal recovery apparatus of the present invention is not limited to the metal recovery apparatus 1 described above.
For example, the metal recovery apparatus of the present invention may be an apparatus that can perform membrane filtration in a state where a membrane module having a filtration membrane is directly immersed in a reaction liquid storage tank.

  Moreover, the apparatus which performs the reaction which reduce | restores the metal ion in a metal ion containing solution with a reducing agent, and obtains metal microparticles in piping before a reaction liquid storage tank may be used, or the apparatus which provided the reaction tank before the reaction liquid storage tank Good. When carrying out the reduction reaction, it is preferable to further act divalent iron ions in terms of improving the reduction reaction efficiency. The form of the divalent iron ion is not particularly limited, but a water-soluble salt or an aqueous solution thereof is preferable. Although it does not specifically limit as a water-soluble salt of divalent iron, Iron sulfate (II), Iron chloride (II), Iron acetate (II), Ammonium iron sulfate (II), etc. are mentioned, Iron (II) sulfate, Iron (II) chloride is preferred. Further, when the metal fine particles catalyze the reduction of the metal ions by the reducing agent, it is preferable that a metal obtained by reducing the metal ions coexists in the reaction liquid storage tank in order to improve the reduction reaction efficiency.

  When the reducing agent remains in the filtered water, for example, a membrane capable of concentrating the remaining reducing agent, such as a reverse osmosis membrane, and an aqueous solution containing the concentrated reducing agent are stored in a reaction liquid storage tank or a reducing agent reservoir. It is good also as an apparatus which provides the return line which returns to a tank, and collects and uses the reducing agent which remained in filtered water.

<Metal recovery method>
Hereinafter, a method using the above-described metal recovery apparatus 1 will be described as an example of the metal recovery method of the present invention.
Metal recovery apparatus in the metal recovery method using 1, reaction metal ions contained in the reservoir 10 solution W _0, to supply the reducing agent B, in the reaction solution reservoir 10, the reducing agent B in the metal ion-containing solution W ₀ The metal fine particle-containing solution W ₁ obtained by reducing the metal ions in the metal ion-containing solution W ₀ with the reducing agent is transferred to the concentration unit 14.
Specifically, the metal ion-containing solution W ₀ is supplied from the metal ion-containing solution storage tank 20 through the pipe 50 to the reaction liquid storage tank 10 while being stirred by the stirring blade 10 a, and the reducing agent B is supplied from the reducing agent storage tank 24. Supply.
Further, in the reaction liquid storage tank 10, metal ions in the metal ion-containing solution are reduced by the reducing agent B to form metal fine particles, and a part of the metal fine particle-containing solution W ₁ is transferred to the concentration unit 14 through the pipe 42.

The reducing agent used in the present embodiment is not particularly limited as long as it is water-soluble and has the ability to reduce the target metal ion to a metal. However, since it is inexpensive and excellent in biodegradability, it has 1 to 5 carbon atoms. Are preferably used, and formic acid and / or a salt thereof are particularly preferably used.
One or more elements selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os, so-called noble metal ions, are reduced to form fine metal particles. Therefore, the metal ion of the metal-containing solution W in ₀ can be recovered as the metal microparticles.

The supply amount ratio of the metal ion-containing solution W ₀ and the reducing agent B to the reaction liquid storage tank 10 is such that the theoretical initial concentration of the metal ions and the reducing agent B in the reaction liquid storage tank 10 is reduced by the reducing agent. However, the conditions should be suitable for forming metal fine particles.
The theoretical initial concentration refers to the concentration of the metal ion-containing solution W ₀ and the reducing agent B in the reaction solution when not reacted.
The theoretical initial concentration of the metal ions in the reaction solution in the reaction solution storage tank 10 is preferably 0.01 to 10 mM from the viewpoint that the reduction reaction efficiency is better when the metal ions are dissolved. ˜5 mM is more preferred.
The theoretical initial concentration of the reducing agent B in the reaction liquid in the reaction liquid storage tank 10 is preferably 0.2 to 200 mM from the viewpoint that the efficiency of reducing metal ions with the reducing agent to form metal fine particles is better. ˜50 mM is more preferred.

The pH of the reaction solution in the reaction solution storage tank 10 is not particularly limited, and can take a suitable value depending on the properties of the metal ion-containing solution W ₀ and the reducing agent B, but from the viewpoint of avoiding the precipitation of the metal hydroxide. 7 or less is preferable and 5 or less is more preferable. The lower limit of the pH is not particularly limited, but is preferably 0 or more from the viewpoint of safety during handling and avoiding the influence of corrosion on the apparatus.
The temperature of the reaction liquid in the reaction liquid storage tank 10 is not particularly limited, and can take a more suitable value depending on the properties of the metal ion-containing solution W ₀ and the reducing agent B, but is preferably 0 to 100 ° C., 20-100 degreeC is more preferable.
Moreover, it is preferable to make a bivalent iron ion act on the reaction liquid storage tank 10 at the point which improves a reduction reaction efficiency.
Although the time at which the divalent iron ions are allowed to act is not particularly limited, from the viewpoint of further improving the efficiency of the reduction reaction, it is preferable to act before supplying the metal ion-containing solution W ₀ and the reducing agent B or immediately after the start of the supply. .
The concentration at which divalent iron ions act is preferably 1 ppm by mass or more, more preferably 5 ppm by mass or more, and even more preferably 20 ppm by mass or more from the viewpoint of better reduction reaction efficiency. The upper limit of the concentration is not particularly limited, but is preferably set to 100 mass ppm or less from the viewpoint of preventing the quality of the recovered metal from deteriorating due to the mixing of trivalent iron precipitates. When the metal fine particles catalyze the reduction of the metal ions by the reducing agent, by further acting the divalent iron ions, the divalent iron ions are allowed to act after the target metal ions are reduced to form the metal fine particles. It does not have to be.

Moreover, it is preferable to coexist the metal which reduces this metal ion with the reaction liquid storage tank 10 at the point which improves reduction reaction efficiency. The timing of coexisting the metal is not particularly limited, but from the viewpoint of further improving the efficiency of the reduction reaction, it is preferable to coexist before supplying the metal ion-containing solution W ₀ and the reducing agent B or immediately after starting the supply.
The amount of coexistence is not particularly limited, but is preferably 1% to 200% of the amount produced when batch reaction is performed in the reaction liquid storage tank 10.
The form of the metal is not particularly limited, but it is preferable that the particle diameter be 0.01 μm to 1 mm because increasing the surface area further improves the reduction reaction efficiency.

When performing the reduction step in a semi-batch reaction, the metal ion-containing solution W _0, feed to the reaction solution reservoir 10 of the reducing agent B is feed rate to the reaction solution reservoir 10 of the metal fine particle-containing solution W ₁ In consideration of the above, the reaction liquid in the reaction liquid storage tank 10 is adjusted within a range in which a predetermined amount can be maintained. The supply of the metal ion-containing solution W ₀ and the reducing agent B to the reaction liquid storage tank 10 may be continuous or intermittent as long as the reaction liquid in the reaction liquid storage tank 10 can be maintained at a predetermined amount. Also good.

When the reduction step is performed by a half-batch reaction, the transfer of the fine metal particle-containing solution W ₁ from the reaction liquid storage tank 10 to the concentration unit 14 has an average residence time (HRT) of the reaction liquid in the reaction liquid storage tank 10. What is necessary is just to adjust so that it may become desired time. The average residence time (HRT) of the reaction liquid in the reaction liquid storage tank 10 may be a time during which a desired reduction reaction rate can be achieved when a batch reaction is performed from the theoretical initial concentrations of metal ions and a reducing agent. .

In the concentration unit 14, the metal fine particle-containing solution W ₁ transferred from the reaction solution storage tank 10 is filtered by the filtration membrane of the membrane module 14 by operating the filtration pump 48. Thus, the metal fine particle-containing solution W ₁ is concentrated.
The effective membrane area of the membrane module is not particularly limited, and may be a membrane area that allows a desired amount of filtered water to be obtained with a filtration pump. When obtaining a desired amount of filtered water with a filtration pump, the membrane area should have a filtration linear velocity (LV) of 0.1 to 1 m / day, so that the filtration efficiency is good and the membrane is blocked. To preferred.
Further, the solution containing metal fine particles is concentrated by membrane filtration, and the metal fine particle-containing concentrated solution W ₂ (concentrated liquid) is returned to the reaction liquid storage tank 10 to contain the metal fine particles in the reaction liquid storage tank 10. metal particle concentration of the solution W ₁ increases. The metal fine particle-containing solution W _{1 that} has risen to a desired concentration can be recovered by the recovery unit 16 through the pipe 44.
Further, the filtered water W ₃ filtered by the filtration membrane, and stored in recovered filtered water storage tank 18 through the pipe 46, is discharged into rivers or the like to adjust the pH as needed.

The use of the metal recovered by the metal recovery method of the present embodiment is not particularly limited. In this embodiment, the metal fine particles are in an aggregated state, and can be used as a catalyst or the like as they are.
Moreover, after removing impurities, such as a reducing agent, by baking metal fine particles with an electric furnace etc., you may use the collect | recovered metal fine particles or metal lump.

In the metal recovery method according to the present invention described above, a solution containing metal fine particles obtained by reducing metal ions contained in a metal-containing solution with a water-soluble reducing agent in a reaction liquid storage tank is concentrated by membrane filtration. Since a concentrated liquid containing metal fine particles can be obtained, the metal can be recovered from the metal-containing solution with high efficiency.
Further, since it is not necessary to use an adsorbent or a microorganism to recover the metal, purification after the recovery is simple.

  The metal recovery method of the present invention is not limited to the method using the metal recovery apparatus 1 described above. For example, the method using the apparatus which can perform membrane filtration in the state in which the membrane module which has a filtration membrane was directly immersed in the reaction liquid storage tank may be used.

  Moreover, the method of performing the reaction which reduces the metal ion in a metal ion containing solution with a reducing agent, and makes it a metal microparticle in piping before a reaction liquid storage tank may be sufficient, and the apparatus which provided the reaction tank before the reaction liquid storage tank is provided. The method used may be used.

  When the reducing agent remains in the filtered water, the remaining reducing agent is concentrated using a membrane that can concentrate the reducing agent such as a reverse osmosis membrane, and an aqueous solution containing the concentrated reducing agent is added to the reaction solution. It is good also as a method of sending to a storage tank or a reducing agent storage tank, and collect | recovering and using the remaining reducing agent.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by the following description.

[Filtration membrane]
A composite hollow fiber membrane (outer diameter 2.8 mm, nominal pore diameter 0.05 μm, manufactured by Mitsubishi Rayon Co., Ltd.) made of polyvinylidene fluoride (PVDF) resin was used for the membrane module.
As the membrane filter, a membrane (MF-Millipore, diameter 47 mm, nominal pore size 0.05 μm) made of cellulose mixed ester was used.

[Pd (II) concentration]
The concentration of Pd (II) in the solution was measured by ICP emission spectroscopy. As a measuring device, an ICP emission spectroscopic analyzer (Shimadzu Corporation, ICEP-9000) was used.

[Example 1]
A 1.25 mM palladium chloride (II) hydrochloric acid aqueous solution (pH 2.7) in the reaction solution storage tank 10 of the metal recovery apparatus 1 illustrated in FIG. 1 so that the theoretical initial concentration of the reaction solution satisfies the following conditions. 240 mL and 60 mL of 250 mM sodium formate aqueous solution (pH 6.8) as a reducing agent were supplied to make a total of 300 mL. The pH of the mixed solution at this time was 5.8.
Pd (II) concentration: 1 mM
Sodium formate concentration: 50 mM
The inside of the reaction liquid storage tank 10 was heated to 40 ° C. and stirred to carry out a reduction reaction. 55 minutes after the start of the reaction, the initially yellow reaction solution became colorless and precipitation of black Pd fine particles was observed. 5 minutes later (1 hour after the start of the reaction), a part of the solution W ₁ containing Pd fine particles was collected and filtered through a 0.05 μm membrane filter. When the Pd concentration of the filtrate obtained here was measured, it was about 1 ppm by mass.
Then, while supplying 1.25 mM palladium chloride (II) hydrochloric acid aqueous solution (pH 2.7) at 240 mL per hour and 250 mM sodium formate aqueous solution (pH 6.8) at 60 mL per hour, the membrane module 14 The membrane was filtered to separate the concentrate W ₂ and the filtrate W _3, and the concentrate W ₂ was returned to the reaction solution storage tank 10 to concentrate the Pd fine particles in the reaction solution storage tank 10. At this time, the extraction rate of the filtered water W ₃ is set to 300 mL / hour so that the average liquid residence time (HRT) of the reaction solution is 1 hour, and the amount of the solution W ₁ containing Pd fine particles contained in the reaction solution storage tank 10. Was maintained at 300 mL. At this time, the filtration linear velocity (LV) was 0.2 m / day.
Measurement of the concentration of Pd filtered water _{W 3,} was about 1 wt ppm.
From this, it was found that 99% or more of the palladium contained in the 1.25 mM palladium chloride (II) hydrochloric acid aqueous solution was concentrated and trapped as fine particles in the reaction solution storage tank 10 and the membrane module 14.
12 hours after the start of the reaction, the solution W ₁ containing Pd fine particles was recovered from the reaction liquid storage tank 10 to the recovery unit 16 at 10 mL per hour. At this time, withdrawal rate of the filtered water _{W 3} being the hourly 290 mL, the amount of the solution _{W 1} containing concentrate Pd fine particles was maintained at 300 mL. The concentrate W ₂ obtained by collecting portion 16 was measured Pd concentration of the filtrate was filtered through a 0.05μm membrane filter, was about 1 wt ppm. The Pd content in the filter residue of the membrane filter was 98% or more.

[Example 2]
300 mL of the solution W ₁ containing Pd fine particles 1 hour after the start of the reaction in Example 1 was filtered through a 0.05 μm membrane filter to obtain Pd fine particles.
Most of the solution was charged into the reaction liquid storage tank 10 of the metal recovery apparatus 1 illustrated in FIG. 1, and then the reaction liquid storage tank 10 was charged with 80 mL of 1.25 mM palladium chloride (II) hydrochloric acid aqueous solution (pH 2.7). Then, 20 mL of a 250 mM sodium formate aqueous solution (pH 6.8) as a reducing agent was supplied to make a total of 100 mL, and then the reaction solution storage tank 10 was heated to 40 ° C. and stirred, in the presence of Pd fine particles. A reduction reaction was performed.
After 15 minutes from the start of the reaction, the reaction solution which was initially yellow became colorless and precipitation of black Pd fine particles was observed. Five minutes later (20 minutes after the start of the reaction), a part of the solution W ₁ containing Pd fine particles was collected, and when the Pd concentration of the filtrate filtered through a 0.05 μm membrane filter was measured, it was about 1 ppm by mass. It was.
Then, while supplying 1.25 mM palladium chloride (II) hydrochloric acid aqueous solution (pH 2.7) at 240 mL per hour and 250 mM sodium formate aqueous solution (pH 6.8) at 60 mL per hour, the membrane module 14 The membrane was filtered to separate the concentrate W ₂ and the filtrate W _3, and the concentrate W ₂ was returned to the reaction solution storage tank 10 to concentrate the Pd fine particles in the reaction solution storage tank 10. At this time, the extraction rate of the filtered water W ₃ is set to 300 mL / hour so that the average liquid residence time (HRT) of the reaction solution is 20 minutes, and the amount of the solution W ₁ containing Pd fine particles contained in the reaction solution storage tank 10. Was maintained at 100 mL. At this time, the filtration linear velocity (LV) was 0.2 m / day.
Measurement of the concentration of Pd filtered water _{W 3,} was about 1 wt ppm.
From this, it was found that 99% or more of palladium contained in the 1.25 mM palladium chloride (II) hydrochloric acid aqueous solution was concentrated and trapped as fine particles in the reaction solution storage tank 10 and the membrane module 14.
Twelve hours after the start of the reaction, the concentrated solution W ₁ was continuously collected from the reaction solution storage tank 10 into the collection unit 16 at 10 mL / hour. At this time, the extraction speed of the filtered water W ₃ was 290 mL per hour, and the amount of the solution W ₁ containing Pd fine particles contained in the reaction liquid storage tank 10 was maintained at 100 mL. The concentrate W ₁ obtained in recovery unit 16 was measured Pd concentration of the filtrate was filtered through a 0.05μm membrane filter, was about 1 wt ppm. The Pd content in the filter residue of the membrane filter was 98% or more.

[Example 3]
In the reaction liquid storage tank 10 of the metal recovery apparatus 1 illustrated in FIG. 1, 80 mL of 1.25 mM palladium (II) chloride acidic aqueous solution (pH 2.7) and 250 mM sodium formate aqueous solution (pH 6.8) as a reducing agent. 20 mL is supplied to make a total of 100 mL, 1 mL of 50 mmol / kg sulfuric acid aqueous solution of 200 mmol / kg iron (II) sulfate is added, the inside of the reaction solution storage tank 10 is heated to 40 ° C., stirred, and Pd fine particles The reduction reaction was performed in the presence.
Five minutes after the start of the reaction, the initially yellow reaction solution became colorless and precipitation of black Pd fine particles was observed. Five minutes later (10 minutes after the start of the reaction), a part of the solution W ₁ containing Pd fine particles was collected, and the Pd concentration of the filtrate filtered through a 0.05 μm membrane filter was measured. It was.
Then, while supplying 1.25 mM palladium chloride (II) hydrochloric acid aqueous solution (pH 2.7) at 240 mL per hour and 250 mM sodium formate aqueous solution (pH 6.8) at 60 mL per hour, the membrane module 14 The membrane was filtered to separate the concentrate W ₂ and the filtrate W _3, and the concentrate W ₂ was returned to the reaction solution storage tank 10 to concentrate the Pd fine particles in the reaction solution storage tank 10. At this time, the extraction rate of the filtered water W ₃ is set to 300 mL / hour so that the average liquid residence time (HRT) of the reaction solution is 20 minutes, and the amount of the solution W ₁ containing Pd fine particles contained in the reaction solution storage tank 10. Was maintained at 100 mL. At this time, the filtration linear velocity (LV) was 0.2 m / day.
Measurement of the concentration of Pd filtered water _{W 3,} was about 1 wt ppm.
From this, it was found that 99% or more of palladium contained in the 1.25 mM palladium chloride (II) hydrochloric acid aqueous solution was concentrated and trapped as fine particles in the reaction solution storage tank 10 and the membrane module 14.
Twelve hours after the start of the reaction, the concentrated solution W ₁ was continuously collected from the reaction solution storage tank 10 into the collection unit 16 at 10 mL / hour. At this time, the extraction speed of the filtered water W ₃ was 290 mL per hour, and the amount of the solution W ₁ containing Pd fine particles contained in the reaction liquid storage tank 10 was maintained at 100 mL. A concentrate W ₁ obtained in recovery unit 16 was measured Pd concentration of the filtrate was filtered through a 0.05μm membrane filter, was about 1 wt ppm. The Pd content in the filter residue of the membrane filter was 98% or more.

[Comparative Example 1]
After supplying 240 mL of 1.25 mM palladium (II) hydrochloric acid acidic aqueous solution (pH 2.7) and 60 mL of water to the reaction solution storage tank 10 of the metal recovery apparatus 1 illustrated in FIG. As described above, 2.2 g of a hydrogen storage alloy (lanthanum-nickel alloy powder previously stored with hydrogen at 30 ° C. and 1.8 MPa for 3 hours) was added, and the inside of the reaction liquid storage tank 10 was heated to 40 ° C. The reduction reaction was carried out with stirring for a period of time. One hour later, a part of the solution W ₁ containing the hydrogen storage alloy powder and Pd fine particles was collected, and the Pd concentration of the filtrate filtered through a 0.05 μm membrane filter was measured. 98% of the solid content thus obtained was derived from a hydrogen storage alloy.

  A summary of the examples and comparative examples is shown in Table 1.

From Table 1, Examples 1-3 using a water-soluble reducing agent had the effect that the solid content which has a palladium fine particle as a main component was obtained.
In particular, in Example 3 in which divalent iron ions were allowed to act, the precipitation of palladium fine particles was accelerated and the reaction efficiency was good.
On the other hand, in Comparative Example 1 using the hydrogen storage alloy powder, 98% of the solid content obtained was derived from the hydrogen storage alloy as compared with Examples 1 to 3.
Therefore, according to the present invention, a highly pure metal can be concentrated and recovered efficiently and simply.

DESCRIPTION OF SYMBOLS 1 Metal recovery apparatus 10 Reaction liquid storage tank 14 Membrane module 16 Recovery part 58 Return part

Claims (9)

A method for recovering a metal from a solution containing metal ions, comprising the following steps (1) and (2).
(1) A reduction step in which a water-soluble reducing agent is allowed to act on a metal ion-containing solution to reduce metal ions to form metal fine particles;
(2) A concentration step of concentrating the solution containing the metal fine particles obtained in the step (1) with a filtration membrane to obtain a concentrated solution; Furthermore, the metal collection | recovery method of Claim 1 including the following process (3).
(3) A returning step of returning the concentrate obtained in the step (2) to the step (1);   The metal recovery method according to claim 1 or 2, wherein in the step (1), divalent iron ions are further allowed to act.   The metal recovery method according to any one of claims 1 to 3, wherein in the step (1), a metal obtained by reducing the metal ions is previously contained.   The metal recovery according to any one of claims 1 to 4, wherein the metal ion is an ion of one or more elements selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os. Method.   The metal recovery method according to any one of claims 1 to 5, wherein the water-soluble reducing agent is an aliphatic aldehyde having 1 to 5 carbon atoms.   The metal recovery method according to claim 6, wherein the aliphatic aldehyde having 1 to 5 carbon atoms is formic acid and / or a salt thereof. A metal recovery apparatus comprising the following (a) and (b).
(A) A storage unit for storing a liquid containing metal fine particles obtained by allowing a water-soluble reducing agent to act on a solution containing metal ions;
(B) A concentration unit that concentrates the liquid containing the metal fine particles in the step (a) with a filtration membrane; Furthermore, the metal collection | recovery apparatus of Claim 8 including the following process (c).
(D) a return unit that returns the concentrate obtained in the step (b) to the step (a);