JPWO2005111272A1 - Method for producing fine particles by plasma-induced electrolysis - Google Patents

Abstract

The present invention includes the following inventions. Electrolyze oxides of metal species (metals belonging to Group 3, 4, 5, 6, 7, 8, 9, 9, 10, 11, 12, 13, 14) A method for producing fine metal particles, which comprises melting in a bath and performing molten salt electrolysis with a cathode placed in the vicinity of the electrolytic bath. A method for producing metal fine particles, wherein molten salt electrolysis is performed by installing an anode containing the metal species in a molten salt and installing a cathode in the vicinity of an electrolytic bath. Also, used metal recycling methods using these manufacturing methods. A method for recycling a metal, comprising melting a used metal in an electrolytic bath, and installing a cathode in the vicinity of the electrolytic bath and performing molten salt electrolysis to obtain metal fine particles. A method for recycling metal, comprising using a used metal as an anode material and obtaining metal fine particles by performing molten salt electrolysis with a cathode placed in the vicinity of an electrolytic bath.

Description

  The present invention relates to a method for producing and recycling metal fine particles by molten salt electrolysis.

  Metal fine particles have higher functionality than bulk materials and have good product processability, and thus are widely used in the field of industrial materials such as magnetic recording media, photocatalysts, pigments, battery electrodes, and catalysts.

  As a conventional method for producing fine metal particles, a method using plasma induced in a gas by arc discharge or the like has recently attracted attention (for example, Patent Documents 1 and 2). In this technique, a voltage is applied between a discharge electrode and a base material as a raw material that are arranged close to each other to generate plasma, and the base material is evaporated and then solidified to form fine particles. Alternatively, a voltage is applied between a plurality of discharge electrodes arranged close to each other, plasma is generated, a raw material is supplied into the plasma, and the raw material is evaporated and then solidified to form fine particles.

  However, in a conventional manufacturing method using plasma induced by arc discharge in a gas, it is necessary to maintain a discharge starting voltage of several kV and a gas atmosphere of several atmospheres, and the plasma current value is 100 to To reach 200A, expensive equipment / equipment and advanced technology are required. In addition, there is a risk of deterioration and destruction of the device due to high temperatures, and it is not necessarily technically and economically efficient. Furthermore, this technique generally requires a high-purity raw material, and scrap or the like is not used as a raw material.

Accordingly, there is a demand for a method for easily generating metal fine particles under safe conditions or an inexpensive apparatus. In addition, if metal fine particles can be obtained not only from pure metal compounds but also from scrap-like, massive metal compounds, and (oxidized) metal compounds used for various industrial purposes, the metal can be reused. It is possible and is very desirable from the viewpoint of the global environment.
JP 2002-241811 A JP 2002-045684 A

  The main object of the present invention is to provide a method for producing fine metal particles and a method for recycling.

  As a result of intensive studies, the inventor has found that the above object can be achieved by carrying out molten salt electrolysis by containing a raw material of metal fine particles in a molten salt or an anode, and has completed the present invention. It was.

That is, the present invention relates to a method for producing the following metal fine particles.
Item 1.
Of at least one metal selected from the group consisting of metals belonging to Group 3, Group 4, Group 5, Group 6, Group 7, Group 8, Group 9, Group 10, Group 11, Group 12, Group 13 and Group 14. A method for producing fine metal particles, comprising melting a metal raw material containing an oxide in an electrolytic bath and placing a cathode in the vicinity of the electrolytic bath to perform molten salt electrolysis.
Item 2.
Item 1. The metal raw material contains an oxide of at least one metal selected from the group consisting of titanium, zirconium, vanadium, niobium, tantalum, molybdenum, tungsten, chromium, platinum, cobalt, nickel, and silicon. The method described in 1.
Item 3.
Of at least one metal selected from the group consisting of metals belonging to Group 3, Group 4, Group 5, Group 6, Group 7, Group 8, Group 9, Group 10, Group 11, Group 12, Group 13 and Group 14. A method for producing metal fine particles, wherein an anode containing at least one selected from the group consisting of the metal and a compound of the metal is placed in the molten salt, and the cathode is placed in the vicinity of the electrolytic bath to thereby perform molten salt electrolysis A method for producing metal fine particles, characterized in that:
Item 4.
Item 4. The method according to Item 3, wherein the molten salt contains at least one selected from the group consisting of a metal and a metal compound as a raw material for the metal fine particles.
Item 5.
Item 5. The method according to any one of Items 1 to 4, wherein molten salt electrolysis is performed by installing an electrical resistance between the power source and the anode.
Item 6.
A method for recycling a metal, comprising melting a used metal in an electrolytic bath, and installing a cathode in the vicinity of the electrolytic bath and performing molten salt electrolysis to obtain metal fine particles.
Item 7.
A method for recycling metal, comprising using a used metal as an anode material and obtaining metal fine particles by performing molten salt electrolysis with a cathode placed in the vicinity of an electrolytic bath. The present invention relates to a method for producing a metal raw material (a material that becomes a raw material for metal fine particles) in a molten salt as metal fine particles by placing a cathode in the vicinity of an electrolytic bath without contacting the electrolytic bath and inducing plasma. . That is, at least one selected from the group consisting of metals belonging to Group 3, Group 4, Group 5, Group 6, Group 7, Group 8, Group 9, Group 10, Group 11, Group 12, Group 13 and Group 14 A method for producing metal fine particles (hereinafter referred to as production method 1), wherein a metal raw material containing a metal oxide is dissolved in an electrolytic bath, and electrolysis is performed by inducing plasma by placing a cathode near the electrolytic bath. May be referred to). In this method, metal fine particles are produced by performing plasma discharge on a metal raw material in a molten salt.

  Further, the present invention is (1) from the group consisting of metals belonging to Group 3, Group 4, Group 5, Group 6, Group 7, Group 8, Group 9, Group 10, Group 11, Group 12, Group 13 and Group 14 An anode containing at least one selected from the group consisting of (2) a compound of the metal; and an anode containing the at least one selected from the group consisting of: The present invention relates to a method for producing fine metal particles (hereinafter, also referred to as production method 2) characterized by performing electrolysis. In this method, the metal or metal compound contained in the anode is ionized and eluted into the molten salt by molten salt electrolysis. And when the metal and / or metal compound (it is not limited to a metal oxide) used as the raw material of fine particles are added in the molten salt, these raw materials are consumed as metal fine particles near the cathode. The raw material is supplied from the anode, and the metal fine particles can be continuously produced. Alternatively, when the metal or metal compound that is the raw material of the fine particles is not added to the molten salt, the metal or metal compound eluted from the anode is subjected to plasma discharge near the cathode to produce metal fine particles.

  In these production methods, when metal fine particles are obtained using a metal oxide (for example, a used metal oxide) as a raw material, it is very excellent in terms of economy and recycling.

  The method of the present invention will be described below. The apparatus for performing molten salt electrolysis in the present invention may be an apparatus generally used when performing molten salt electrolysis.

Electrolytic bath In the present invention, an electrolytic bath generally used in molten salt electrolysis can be used as the electrolytic bath. For example, alkali metal halide, alkaline earth metal halide, alkali metal carbonate, alkaline earth metal carbonate, alkali metal sulfate, alkaline earth metal sulfate, alkali metal nitrate, alkaline earth metal nitrate, etc. It is preferable to use a molten salt obtained by singly or in combination of two or more as a solvent for an electrolytic bath.

LiF, NaF, KF, RbF, CsF, LiCl, NaCl, KCl, RbCl, CsCl, LiBr, NaBr, KBr, RbBr, CsBr, LiI, NaI, KI, RbI, CsI, etc. are used as alkali metal halides can, halides of alkaline earth _{metals, MgF 2, CaF 2, SrF} 2, BaF 2, MgCl 2, CaCl 2, SrCl 2, BaCl 2, MgBr 2, CaBr 2, SrBr 2, BaBr 2, MgI 2 , CaI ₂ , SrI ₂ , BaI _{2 and the} like can be used.

  The said compound can also be used independently and can also be used in combination of 2 or more type. The combination of these compounds, the number of compounds to be combined, the mixing ratio, and the like are not limited, and can be appropriately selected according to the type of metal to be electrolyzed. In the present invention, KCl and / or LiCl melted (LiCl: KCl = about 35 mol% to 100 mol%: about 65 mol% to 0 mol%, preferably about 55 mol% to 65 mol%: about 45 mol% to 35 mol%) , NaCl and KCl melted (NaCl: KCl = about 30 mol% to 70 mol%: about 70 mol% to 30 mol%, preferably about 45 mol% to 55 mol%: about 55 mol% to 45 mol%), LiCl, KCl and CsCl (A eutectic composition of LiCl: KCl: CsCl = 57.5: 13.3: 29.2 mol% is preferable, but the composition ratio may be changed by about 20%).

  In such a solvent, a metal compound (hereinafter sometimes referred to as “metal raw material” or “ion source”) as a raw material for metal fine particles is dissolved, and molten metal electrolysis is performed to obtain metal fine particles. it can. Moreover, when the metal or metal compound used as the raw material of metal fine particles is contained in the anode, addition of the metal raw material to the molten salt is optional.

  Further, the electrolytic bath in the present invention may contain other impurities, a solubilizing agent, an electrolysis auxiliary agent and the like as long as the properties of the obtained metal fine particles are not impaired.

Metal raw material (ion source)
The metal fine particles obtained by the method of the present invention are from metals belonging to Group 3, Group 4, Group 5, Group 6, Group 7, Group 8, Group 9, Group 11, Group 11, Group 12, Group 13 and Group 14. At least one metal fine particle selected from the group consisting of: Among the metals, titanium (Ti), zirconium (Zr), vanadium (V), niobium (Nb), tantalum (Ta), molybdenum (Mo), tungsten (W), chromium (Cr), platinum (Pt), At least one selected from the group consisting of cobalt (Co), nickel (Ni), and silicon (Si) is more preferable.

  Therefore, in the production method 1, at least one of the above metal oxides is contained in the electrolytic bath as a metal raw material to be a raw material for these metal fine particles. The metal raw material may be composed of the above metal oxide, or may be a mixture of a metal oxide and a metal or a metal compound. Furthermore, other components may be included.

Examples of titanium oxide include TiO, TiO ₂ and Ti ₂ O ₃ ; examples of zirconium oxide include ZrO ₂ ; and examples of vanadium oxide include VO, VO ₂ , V ₂ O ₃ , and V ₂ O _4. , V ₃ O ₅ and the like. Examples of the oxides of _{niobium, NbO, NbO 2, Nb 2} O 5 or the like; TaO as tantalum oxide, Ta ₂ O ₅ or the like; MoO ₂ as an oxide of molybdenum, MoO ₃ etc; the oxides of _{chromium, CrO, CrO 2, Cr 2} O 3 or the like;; WO _2, WO _3, etc. as the tungsten oxide PtO as oxides of platinum, Pt ₃ O _4, PtO ₂ and the like; Examples of cobalt oxides include CoO and Co ₃ O ₄ ; examples of nickel oxides include NiO and Ni _1-x O (0.003 <x <0.17); examples of silicon oxides include SiO and SiO _2. It is done.

  The metal oxide may be a naturally oxidized metal or a used metal used for various purposes. As the used metal, for example, a metal used in a magnetic recording medium, a photocatalyst, a pigment, a fuel cell, a catalyst, or the like can be used. By performing molten salt electrolysis using such a metal oxide, the used metal can be recycled.

  When the metal type of the metal raw material to be used is one kind, metal fine particles composed of a single metal atom can be obtained. When the metal type of the metal raw material to be used is two or more types, Metal fine particles (made of metal) can also be obtained. Therefore, metal fine particles include alloy fine particles.

As the metal compound, sulfates, nitrates, phosphates, halides (chlorides, fluorides, bromides, iodides, etc.) of the above metals can be used. For example, K ₂ TaF ₇ , NiCl ₂ , K ₂ TiF ₆ , AgCl, K ₂ TaF ₆ , VCl ₂ , K ₂ NbF ₇ , K ₂ MoO ₄ , K ₂ WO ₄ , CrCl ₂ , K ₂ PtCl ₆ , CoCl ₂ K ₂ SiF ₆ is exemplified. The said metal compound can also be used independently and can also use 2 or more types together.

  In the method of the present invention, the shape of the metal raw material to be used is not limited. For example, it may be in the form of powder, and may be in various shapes such as scrap and lump. Moreover, after using for various uses, it is also possible to take out a metal part and to use it as it is.

  The amount of the above-described metal compound and / or metal oxide added to the electrolytic bath is not limited, and can be appropriately selected according to the electrolysis time and the amount and size of the fine particles. For example, the metal raw material may be dissolved so as to be about 0.0001 to 10 mol / L, preferably about 0.1 to 5.0 mol / L per solvent of the electrolytic bath.

  In the production method 2 of the present invention, since the metal raw material is supplied from the anode by electrolysis, the addition of the metal raw material to the electrolytic bath can be arbitrarily selected. In the case where a metal raw material is added to the electrolytic bath, the metal raw material may be one selected from the group consisting of a metal and a metal compound as a raw material for fine particles. Therefore, in the production method 1, a metal oxide is essential as a metal raw material, but in the production method 2, the metal raw material added to the molten salt is not limited to the metal oxide, and a metal or a metal compound can be widely used. . Moreover, in the manufacturing method 2, since the metal raw material is supplied from the anode, it is possible to reduce the concentration of the metal raw material added to the molten salt as compared with the case of the manufacturing method 1. When the metal type of the metal raw material supplied from the anode is different from the metal type of the metal raw material added to the molten salt, alloy fine particles are obtained. Is included.

electrode
(1) Anode In the production method 1 of the present invention, as the anode, an electrode generally used as an anode in molten salt electrolysis can be used and is not particularly limited. For example, carbon materials such as glassy carbon, graphite, and conductive diamond, tantalum, tungsten, molybdenum, platinum, and the like can be used as electrodes. A material in which a metal such as tantalum, tungsten, molybdenum, or platinum is formed in a thin film on a different material can also be used as the anode. Moreover, a used metal can also be used as an anode material. Moreover, when it is calculated | required that generation | occurrence | production of chlorine gas is calculated | required, it can suppress by making a fine particle raw material metal or the compound of this metal contain in an anode.

  In addition, in the production method 2 of the present invention, the anode comprises (1) group 3, group 4, group 5, group 6, group 7, group 8, group 9, group 10, group 11, group 12, group 13 and 14 At least one metal selected from the group consisting of metals belonging to the group; and (2) at least one selected from the group consisting of compounds of the metals. The preferred metal species is the same as the preferred metal species of the metal fine particles. The metal compound is the same as the metal compound in the metal raw material. In this production method, generation of chlorine gas is suppressed because the anode contains a fine particle raw material. When two or more kinds of metal species are used for the anode, the base metal becomes fine particles. Therefore, the combination of metal species contained in the anode is appropriately selected according to the metal species of the target fine particles.

  The shape and size of the electrode used in the present invention are not limited. As the shape of the electrode, for example, a plate shape, a rod shape, a lump shape, a spring shape, a prismatic shape, or the like can be used.

  When electrolysis is performed in the present invention, the anode is preferably immersed in an electrolytic bath so that electrolysis is generally performed. The whole anode may be immersed or a part may be immersed, and the aspect is not particularly limited.

(2) As the cathode, a cathode that is generally used for molten salt electrolysis and can generate plasma can be used, and is not particularly limited. For example, various metals such as iron, nickel, molybdenum, tantalum, and tungsten, alloys thereof, carbon materials such as glassy carbon and conductive diamond, conductive ceramics, semiconductor ceramics, and the like can be used. Moreover, what formed these in the thin film form on the dissimilar material can also be used as a cathode. Among them, it is preferable to use a refractory metal such as tungsten or tantalum which is not easily consumed when plasma is induced.

  In the present invention, it is installed in the vicinity of the electrolytic bath so as not to be in contact with or immersed in the electrolytic bath. The installation location is not particularly limited as long as it is a location where metal fine particles are generated in the molten salt by the plasma generated by the cathode, but it is preferably installed at the upper part of the molten salt liquid surface. By doing so, plasma is induced from the cathode, and fine metal particles are generated in the electrolytic bath. The distance from the surface of the electrolytic bath to the lowest part of the cathode is not limited as long as the plasma is stably induced.

Plasma-Induced Discharge Electrolysis The electrolysis conditions in the present invention can be generally performed under conditions for performing molten salt electrolysis, and can be appropriately selected according to the composition of the solvent, the type of the target metal fine particles, and the like. For example, the applied voltage may be about 200 to 800 V, but about 200 to 400 V is preferable for reducing the burden on the electric circuit. However, it can be lowered to 10 to 200 V, preferably 30 to 150 V, when the generation of plasma-induced discharge is stable. The type of generated current is preferably a direct current, and the current per discharge electrode is about 0.05 to 50 A, preferably about 0.1 to 20 A.

  In the present invention, in order to induce plasma stably, it is preferable to ensure the stability of discharge by inserting an electrical resistance between the power source and the electrode. The electrical resistance can be inserted on the cathode side, the anode side, or both. The type of the electrical resistance is not limited as long as it is a resistor having a capacity capable of withstanding the current during electrolysis. For example, a cement resistor, a hollow resistor, a non-combustible wire fixed resistor, etc. can be used, and a non-combustible wire is used. A fixed resistor is more preferred. The value of the resistance is usually about 1Ω to 5kΩ, preferably 3Ω to 3kΩ.

  The temperature of the electrolytic bath is not limited and can be appropriately selected according to the melting point of the solvent, the melting point of the ion source, and the like. For example, it is about 250-700 degreeC, Preferably it is about 400-500 degreeC.

  The electrolysis is usually performed under atmospheric pressure, but can be performed under pressure or under reduced pressure. Electrolysis is preferably performed in an inert gas atmosphere. Examples of the inert gas include nitrogen, argon, neon, and the like, and argon is preferable.

  The electrolysis time is not limited, and can be appropriately selected according to the type and particle size of the target metal particles. For example, it is about 0.1 to 10 hours, preferably about 1 to 5 hours.

  In the present invention, by adjusting the concentration of the ion source to be added, electrolysis time, etc., metal fine particles having an arbitrary particle diameter can be obtained in a range of about 100 μm or less, preferably in the range of about 1 nm to 100 μm. In particular, in the present invention, nano-sized very small metal particles can be obtained. For example, by reducing the electrolysis time, the time from electrolysis to recovery, reducing the concentration of the ion source in the electrolysis bath, or keeping the temperature of the electrolysis bath low during electrolysis, the size of the metal fine particles can be reduced. can do.

The following may be considered as a mechanism for obtaining metal fine particles by the method of the present invention, but the present invention is not limited to this mechanism. When plasma-induced electrolysis is performed using the discharge electrode as a cathode, the cation M ^{n +} used as the raw material for the fine particles in the solvent is generated according to the following formula (1), and the reduction reaction of the alkali metal ion L ⁺ existing in the solvent ( As represented by the formula (3) along with the formula (2)), it is reduced to an atomic substance.

^{M → M n + + ne -} (1)
^{L + + e - → L (} 2)
nL + M ^{n +} → nL ⁺ + M (3)
Subsequently, atomic level clusters are formed by collisions between atomic substances in the solvent, and further, collisions between atomic level clusters are sequentially repeated to grow to fine particles of several nm or several μm.

When supplying cation M ^{n +} as a raw material of fine particles by anodic dissolution of an oxide or the like held in an electrode part in a solvent or chemical dissolution of an oxide or the like held in a solvent, the following formula (4) ) Or (5), the cation M ^{n +} is produced in the solvent.

^{M → M n + + ne -} (4)
M _x A _y → xM ^{y +} + yA ^x- (5)
(However, M represents a metal contained in an oxide or the like, and M _x A _y represents an oxide or the like.)
There are two types of cations (M ₁ ^{n1 +} , M ₂ ^{n2 +} ) that are the raw materials for fine particles in the solvent, and each ion is reduced at the same time. It is also possible to form. The same applies when there are three or more ionic species.

M ₁ ^{n1 +} + M ₂ ^{n2 +} + (n ₁ + n ₂ ) e ⁻ → M ₁ M ₂ (6)
Recovery of metal fine particles The obtained metal particles can be recovered as follows, but are not limited thereto.

  For example, the molten salt containing metal particles can be taken out of the electrolytic bath, and preferably cooled and solidified under an inert gas atmosphere. The kind of inert gas is as described above. By carrying out in an inert gas atmosphere, oxidation of metal fine particles can be prevented.

  Next, the solidified electrolytic solution may be pulverized and immersed in a cleaning solution. The means for pulverization is not limited, and may be performed, for example, with a hammer, a mixer, or the like, but ultrasonic treatment is preferable from the viewpoint of more efficient and fine pulverization. The apparatus for performing the ultrasonic treatment is not limited, and a commercially available apparatus can be used. The ultrasonic conditions are not limited. For example, ultrasonic treatment may be performed at a frequency of about 10 to 100 kHz and about 20 to 60 kHz for about 100 to 300 minutes, preferably about 150 to 200 minutes, per 100 g of solidified electrolyte. .

  After the ultrasonic treatment, the metal fine particles of the present invention can be obtained by washing and centrifuging. The conditions for the centrifugation are not limited as long as the metal fine particles obtained in the present invention and the solidified electrolyte are separated, and can be appropriately selected. For example, it can be about 1000 to 5000 rpm, preferably about 1500 to 3000 rpm, about 10 minutes to 2 hours, preferably about 30 minutes to 1.5 hours.

  The washing method is not limited as long as the metal fine particles obtained in the present invention can be subjected to ultrasonic waves, centrifugal separation or the like. For example, water or an aqueous solution in which a reducing agent generally used for electroless plating is dissolved can be used. As the reducing agent, borane-amine complexes such as dimethylamine borane and trimethylamine borane; borohydride compounds such as potassium borohydride and sodium borohydride; formaldehyde and the like can be used. These concentrations are not limited.

  If necessary, the sonication and centrifugation of the precipitate may be repeated. By repeating the process, metal fine particles can be obtained with high efficiency from the solidified electrolyte.

  The particle diameter of the obtained metal particles can be determined by a conventional method such as electron microscope observation. The particle size distribution can also be performed by a conventional method such as a dynamic light scattering measurement method. Furthermore, the oxygen content in the metal fine particles can also be determined by a conventional method such as an electroactive gas melting-infrared absorption method.

  It is also possible to use the obtained fine metal particles obtained by further adding a nonionic surfactant, a dispersant containing alcohol or the like to the cleaning solution. The metal fine particles may be washed with an appropriate liquid before use and used for a desired purpose.

Recycling method The recycling method of the present invention uses the above-described method for producing fine metal particles, and uses a used metal or metal compound as a metal raw material. That is, a used metal or metal compound is added to the molten salt as a metal raw material or held on the anode. As a result, metal fine particles corresponding to the metal species of the used metal or metal compound are generated, so that the used metal or metal compound can be reused.

Hereinafter, an example of a preferred embodiment of the present invention will be described with reference to FIG.
For example, a holder (3) for installing a crucible (2) made of high-purity alumina as an electrolytic cell is provided in an electric furnace (1) capable of heating at about 500 ° C. The active gas is circulated through the introduction pipe (4) and the exhaust pipe (5) at atmospheric pressure. An alkali metal halide or the like is melted in the crucible to obtain a solvent (6) for the electrolytic bath. The temperature of the solvent is measured with a thermocouple (7) and set to a predetermined temperature.

  An ion source serving as a raw material for the metal fine particles is added to the solvent while the inert gas is circulated. Next, a power supply device (10) is installed between the discharge electrode (8) disposed on the solvent and the electrode (9) disposed in the solvent, a voltage is applied, and the solvent and the discharge electrode Plasma is induced between them.

  Instead of adding the ion source, the electrode (9) in the solvent may include a portion capable of holding the substance (11) containing the raw material of the metal fine particles. By doing so, the ion source which becomes the raw material of the metal fine particles during electrolysis can be stably or continuously supplied. The ion source may be held in a solvent other than the electrode.

  When plasma is induced, if an electric resistance (12) or the like is inserted between the power supply device and the electrode, the plasma can be stably induced, and electrolysis is promoted, so that metal fine particles are efficiently formed. preferable.

  The method for producing fine metal particles of the present invention is particularly excellent in that not only the metal but also an oxide of the metal can be used as a raw material for the fine metal particles. In addition, by controlling parameters such as the electrolyte composition, electrolyte temperature, and electrolysis time in molten salt electrolysis, the particle size, particle size distribution, and the like of the fine particles can be easily controlled.

  The present invention does not require expensive equipment / equipment, advanced knowledge and advanced technology, and can produce desired fine metal particles, so that the production cost of the metal particles is greatly reduced. Also, the electrolytic bath does not contain harmful substances and can be reused.

  Furthermore, the metal fine particles can be produced even if scrap or lump raw materials are used as the form of the metal raw material used as the raw material for the metal fine particles. For example, an ion source can be supplied by anodic dissolution or chemical dissolution of the substance by holding the substance containing the raw material of the fine particles to be produced in the electrode part disposed in the solvent in the electrolytic bath or in the solvent. it can. That is, since the material necessary for the device can be manufactured again from the state of scrap or the like, the method of the present invention is also excellent as a metal recycling method.

It is a conceptual diagram of the apparatus for performing molten salt electrolysis. (A) shows a scanning electron micrograph of the tantalum fine particles obtained in Example 1, and (b) shows an analysis result by an X-ray microanalyzer for the white rectangular portion of (a). (A) shows a scanning electron micrograph of the tantalum fine particles obtained in Example 3, and (b) shows the result of X-ray diffraction of the tantalum fine particles.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric furnace 2 Crucible 3 Holder 4 Introduction pipe 5 Exhaust pipe 6 Solvent 7 Thermocouple 8 Electrode 9 Electrode 10 Power supply device 11 Raw material holding part 12 Electric resistance

  Hereinafter, examples will be shown to further clarify the features of the present invention. The present invention is not limited to these examples.

Example 1
For the solvent (electrolytic bath), LiCl-KCl (58.5: 41.5 mol%; total 100 g) mixed in the eutectic composition was vacuum-dried at 180 ° C for several days and then melted at 450 ° C in an argon atmosphere. Using. As the tantalum source, potassium heptafluorotantalum (K ₂ TaF ₇ ) was used and added to a concentration of 0.1 mol%.

Tungsten wire is placed on the solvent as the discharge electrode (cathode) and 2.001 g of tantalum capacitor scrap (pin scrap) in the solvent as the anode (the oxide is Ta ₂ O ₅ , the surface is completely oxidized, but the entire scrap A cylindrical tantalum metal electrode having an oxide ratio of about 0.5 wt% was disposed. The solvent temperature was maintained at 450 ° C. under an argon atmosphere, 250 V was applied between the discharge electrode and the electrode in the solvent, plasma was induced between the discharge electrode and the solvent, and electrolysis was performed for 5 hours. .

  After plasma-induced electrolysis, the solvent containing fine particles is cooled and solidified to room temperature in an argon atmosphere, and sonicated in a 2M hydrazine aqueous solution for several hours until the solidified solvent is dissolved, followed by sonication for about 10 minutes. And the centrifugation operation was repeated. Centrifugation was performed at 2000 rpm, the first time being about 10 minutes, the second time being about 30 minutes, and the third time being about 60 minutes.

  As a result, black tantalum fine particles were recovered. When the fine particles were observed with a scanning electron microscope, it was confirmed that nanometer-order fine particles were obtained as shown in FIG. Subsequently, as a result of X-ray microanalyzer measurement on the obtained fine particles (white rectangular portion in FIG. 2 (a)), it was confirmed that tantalum fine particles were formed (FIG. 2 (b)). .

  Further, since the mass of pin scrap in the cylindrical tantalum metal electrode placed in the solvent is reduced to 0.996 g after electrolysis, the tantalum metal or tantalum oxide contained in the pin scrap is dissolved during electrolysis. It was confirmed that On the other hand, the consumption of the cylindrical tantalum metal electrode was 0.325 g.

The theoretical mass of fine particles obtained by electrolysis from 0.1 mol% equivalent K ₂ TaF ₇ added to the solvent is 0.32 g, but the fine particles collected for analysis alone exceed 0.4 g, It can be said that tantalum fine particles were also formed from a tantalum ion source obtained by dissolution from a tantalum metal electrode, and it was confirmed that the present invention can be used as a resource circulation type process using scrap as a raw material.

Example 2
Metal compounds other than tantalum include nickel (using NiCl ₂ as the ion source), titanium (using K ₂ TiF ₆ as the ion source), silver (using AgCl as the ion source), zirconium (K ₂ ZrF ₆ as the ion source) ), Vanadium (using VCl ₂ as the ion source), niobium (using K ₂ NbF ₇ as the ion source), molybdenum (using K ₂ MoO ₄ as the ion source), tungsten (K ₂ WO ₄ as the ion source) ), Chromium (using CrCl ₂ as the ion source), platinum (using K ₂ PtCl ₆ as the ion source), cobalt (using CoCl ₂ as the ion source), and tantalum capacitor scrap (pin When the experiment was performed in the same manner as in Example 1 using scraps (pin scraps) of metal species of the above metal compounds instead of scraps), respective nano-order metal fine particles were obtained.

Example 3
A cylindrical graphite electrode holding 1.502 g of tantalum capacitor scrap (pin scrap) in a solvent as an anode and a current value of 0.80 A for 1.7 hours under conditions that do not contain potassium heptafluorotantalum as an ion source The experiment was performed in the same manner as in Example 1 except that the above was performed. When the obtained fine particles were subjected to X-ray diffraction, it was confirmed that the fine particles were tantalum fine particles having a lattice constant of about 3%.

  The mass of pin scrap in the cylindrical graphite electrode placed in the solvent was reduced to 0.903 g after electrolysis, and tantalum fine particles were formed only from the tantalum ion source obtained by dissolving from the pin scrap. Was confirmed. In this embodiment, tantalum fine particles are formed from an electrode that does not include an ion source in advance in the solvent and that holds only scrap, and the present invention is more effective as a resource circulation type process using only scrap as a raw material. It was confirmed that there was.

Example 4
NiCl ₂ (nickel ion source), K ₂ TiF ₆ (titanium ion source), AgCl (silver ion source), K ₂ ZrF ₆ (zirconium ion source), VCl ₂ (vanadium ion source) ), K ₂ NbF ₇ (niobium ion source), K ₂ MoO ₄ (molybdenum ion source), K ₂ WO ₄ (tungsten ion source), CrCl ₂ (chromium ion source), K ₂ PtCl ₆ (platinum) No ion source) and CoCl ₂ (cobalt ion source) were used in the same manner as in Example 2. As a result, nano-order metal fine particles were obtained.

  In this embodiment, the fine particles of the metal are formed only by the electrode that does not contain the ion source in advance and holds the scrap in the solvent, and the present invention is more effective as a resource circulation type process using scrap as a raw material. It was confirmed.

  The present invention is useful in the field of metal fine particle production and metal recycling.

Claims (7)

  Of at least one metal selected from the group consisting of metals belonging to Group 3, Group 4, Group 5, Group 6, Group 7, Group 8, Group 9, Group 10, Group 11, Group 12, Group 13 and Group 14. A method for producing fine metal particles, comprising melting a metal raw material containing an oxide in an electrolytic bath and placing a cathode in the vicinity of the electrolytic bath to perform molten salt electrolysis.   The metal raw material contains an oxide of at least one metal selected from the group consisting of titanium, zirconium, vanadium, niobium, tantalum, molybdenum, tungsten, chromium, platinum, cobalt, nickel, and silicon. The method according to 1.   Of at least one metal selected from the group consisting of metals belonging to Group 3, Group 4, Group 5, Group 6, Group 7, Group 8, Group 9, Group 10, Group 11, Group 12, Group 13 and Group 14. A method for producing metal fine particles, wherein an anode containing at least one selected from the group consisting of the metal and a compound of the metal is placed in the molten salt, and the cathode is placed in the vicinity of the electrolytic bath to thereby perform molten salt electrolysis A method for producing metal fine particles, characterized in that:   The method according to claim 3, wherein the molten salt contains at least one selected from the group consisting of metals and metal compounds as raw materials for the metal fine particles. The method according to any one of claims 1 to 4, wherein molten salt electrolysis is performed by installing an electrical resistance between the power source and the anode.   A method for recycling a metal, comprising melting a used metal in an electrolytic bath, and installing a cathode in the vicinity of the electrolytic bath and performing molten salt electrolysis to obtain metal fine particles.   A method for recycling metal, comprising using a used metal as an anode material and obtaining metal fine particles by performing molten salt electrolysis with a cathode placed in the vicinity of an electrolytic bath.