JP2013253307A - Method for producing metal particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a metal particle using titanium as a reducing agent, capable of reducing used amount of a pH adjuster.SOLUTION: A method for producing a metal particle includes: a step S110 of preparing a reaction solution including metal ions and tetravalent titanium ions; a step S130 of adding ammonia as a pH adjuster to the reaction solution to alkalinize the reaction solution and stirring the reaction solution; a step S140 of separating a metal particle from the reaction solution; and a step 150 of separating ammonia from the reaction solution by heating and recovering the ammonia. The recovered ammonia is reused as the pH adjuster.

Description

  The present invention relates to a method for producing metal particles in which metal ions are generated by reducing metal ions with trivalent titanium.

As a method for producing metal particles in which metal particles are deposited using trivalent titanium as a reducing agent, the technique described in Patent Document 1 is known.
In this production method, the metal ions are reduced by making the pH of the reaction solution alkaline so that trivalent titanium is more easily oxidized. Thereby, metal particles are deposited.

In such a method for producing metal particles, a technique for reusing titanium as a reducing agent is also known (see Patent Document 2).
Specifically, tetravalent titanium ions are reduced back to trivalent titanium by electrolysis. When electrolysis is performed, a solution containing tetravalent titanium is acidified so that titanium is easily reduced.

In such a production method, the pH of the reaction solution is repeatedly adjusted.
Specifically, in the production of metal particles, a metal salt is dissolved in an alkaline reaction solution to deposit metal particles. Then, the metal particles are separated from the reaction solution to obtain metal particles. After separating the metal particles, the reaction solution is regenerated. That is, the reaction solution is acidified and the reaction solution is electrolyzed. And in the production | generation of the next metal particle, the same process is repeated using the regenerated reaction solution. That is, when the metal is deposited, the reaction solution is made alkaline, and when the reaction solution is electrolyzed, the reaction solution is made acidic.

JP 2003-147416 A JP 2004-18923 A

  Such a method for producing metal particles has an advantage that titanium can be reused. However, since a pH adjuster is used every time metal particles are produced, a large amount of pH adjuster is consumed in mass production of metal particles. Since the pH adjusting agent is not a substance constituting the metal particles, there is a demand for reducing the amount of the pH adjusting agent used.

  The present invention has been made in view of such circumstances, and the object thereof is a method for producing metal particles that can reduce the amount of a pH adjuster used in the method for producing metal particles using titanium as a reducing agent. Is to provide.

  (1) The invention according to claim 1 is a method for producing metal particles in which metal particles are produced by reducing the metal ions in a solution containing trivalent titanium ions and metal ions. Preparing a reaction solution containing metal ions to be reduced by the reaction and trivalent titanium ions, adding ammonia as a pH adjuster to the reaction solution to make the reaction solution alkaline, and stirring the reaction solution A step of separating the metal particles from the reaction solution, and a step of separating ammonia from the reaction solution by heating and recovering the ammonia, and reusing the recovered ammonia as the pH adjuster. The gist.

(2) The invention according to claim 2 is summarized in that in the method for producing metal particles according to claim 1, recovered ammonia and aqueous ammonia are used as the pH adjuster.
In some cases, the pH value of the reaction solution cannot be set to a predetermined value only with the recovered ammonia. Therefore, in the present invention, ammonia water is used as a pH adjuster in addition to the recovered ammonia. Moreover, by using ammonia water as the replenishing ammonia, the pH of the reaction solution can be quickly increased to a predetermined value as compared with the case of using ammonia gas for replenishment.

  (3) The invention according to claim 3 is the method for producing metal particles according to claim 1 or 2, wherein the reaction solution from which the metal particles are separated is acidified, electrolyzed, and trivalent titanium ions are converted. The gist is to regenerate the reaction solution as a containing solution.

  By making the reaction solution acidic, the reduction rate of titanium ions is increased. For this reason, the ratio of trivalent titanium ions to the total amount of titanium ions can be increased by making the reaction solution acidic and then electrolyzing the reaction solution.

  (4) The invention according to claim 4 is the method for producing metal particles according to any one of claims 1 to 3, wherein the ammonia is separated from the reaction solution by heating and the ammonia is recovered. The gist is to recover ammonia by bringing ammonia generated by heating the reaction solution into contact with water. According to this method, since facilities such as a compressor and a cooler are unnecessary, it is possible to recover ammonia with simple facilities as compared with the compression method and the cooling method.

  (5) The invention according to claim 5 is the method for producing metal particles according to any one of claims 1 to 4, wherein the reaction solution is ammonium chloride, trisodium citrate, sodium tartrate, sodium acetate. And at least one complexing agent selected from the group consisting of gluconic acid.

  In this invention, a complexing agent is included in the reaction solution. The complexing agent forms a complex with metal ions and titanium ions, and slows the redox reaction rate of both. That is, the growth of the metal particles can be moderated and the particle size can be reduced as compared with the method of depositing metal without including a complexing agent.

  (6) The invention according to claim 6 is the method for producing metal particles according to any one of claims 1 to 5, wherein the reaction solution is polycarboxylic acid, polyacrylic acid, polyvinyl alcohol, polyvinylpyrrolidone. And at least one dispersant selected from the group consisting of polyethyleneimine.

  The dispersing agent suppresses the growth of metal particles precipitated in the reaction solution and suppresses the metal particles from gathering together. That is, it has a function of inhibiting the formation of secondary particles or aggregates. For this reason, it can suppress that a metal particle becomes large too much and formation of a secondary particle or an aggregated particle by including a dispersing agent in a reaction solution.

  ADVANTAGE OF THE INVENTION According to this invention, in the manufacturing method of the metal particle which uses titanium as a reducing agent, the manufacturing method of the metal particle which can reduce the usage-amount of a pH adjuster can be provided.

The flowchart which shows the manufacturing process of a metal particle. The schematic diagram of a metal particle production | generation apparatus. The schematic diagram of a metal particle production | generation apparatus. The schematic diagram of an electrolysis apparatus. The scanning electron micrograph figure of the metal particle produced | generated by the 1st production | generation. The scanning electron micrograph figure of the metal particle produced | generated by the 2nd production | generation.

[Production method of metal particles]
With reference to FIG. 1, the manufacturing method of a metal particle is demonstrated.
First, a reaction solution is prepared (first step; step S110). Specifically, a metal salt, a reducing agent, a dispersing agent, a complexing agent, and a pH adjusting agent are dissolved in water.

As the reducing agent, trivalent titanium ions are used.
A source of trivalent titanium ions is, for example, titanium trichloride.
Trivalent titanium ions are oxidized by reducing metal ions to become tetravalent titanium ions, but are electrolytically reduced in the subsequent steps to be regenerated into trivalent titanium ions. And it is reused for the production | generation of the next metal particle. For this reason, the supply of trivalent titanium ions is performed during the initial production of metal particles.

The metal salt is selected according to the composition of the metal particles to be generated.
When producing nickel particles, for example, nickel chloride is used.
Trivalent titanium ions can reduce various metal ions. Examples of metal ions reduced by trivalent titanium ions include metal ions such as tungsten, tantalum, rhenium, iron, cobalt, nickel, copper, silver, gold, and platinum. By including these cations in the reaction solution, metal particles having these metals as a composition can be generated. Moreover, it is also possible to produce | generate the metal particle containing 2 or more types of metals by including 2 or more types of metal ions in a reaction solution.

As the dispersant, a substance that suppresses aggregation of metal particles precipitated in the reaction solution and suppresses excessive growth of metal particles is used.
Metal particles having a particle size of 1 μm or less may aggregate in a solution to produce secondary particles. In order to suppress such aggregation of metal particles, a dispersant is included in the reaction solution. For example, polycarboxylic acid, polyacrylic acid, polyvinyl alcohol, polyvinyl pyrrolidone, polyethyleneimine, etc. are used as the dispersant. Moreover, you may select and use 2 or more types from the group of these substances.

  As the complexing agent, one that coordinates to the metal ion and moderates the reduction of the metal ion is used. For example, ammonium chloride, trisodium citrate, sodium tartrate, sodium acetate, gluconic acid and the like are used. Moreover, you may select and use 2 or more types from the group of these substances.

In the next step (second step; step S120), the reaction solution prepared in the first step is made alkaline.
Trivalent titanium ions have the effect of reducing metal ions in alkalinity. For this reason, when depositing metal particles, the reaction solution is made alkaline by dissolving the pH adjuster in the reaction solution.

  As a pH adjuster, at least one of ammonia and aqueous ammonia is used. In the reduction of the metal ions, a base such as sodium carbonate can be used, but in this embodiment, a substance that is gaseous at normal temperature, easily dissolved in water, and exhibits alkalinity is used. That is, a substance that easily recovers the pH adjusting agent after the production of the metal particles is employed as the pH adjusting agent.

  In order to shorten the time for raising the pH of the reaction solution to a predetermined value, it is preferable to use ammonia water together with ammonia gas. Specifically, since the rate of increase in pH due to ammonia gas decreases as the pH increases, ammonia water is additionally charged after a predetermined time has elapsed since the start of ammonia gas supply.

As the ammonia gas, the ammonia recovered in the fifth step shown below is used.
Ammonia water having a constant concentration is used. In addition, you may prepare ammonia water using the ammonia and pure water which were collect | recovered at the 5th process.

  Ammonia mainly has the property of making the pH of the reaction solution alkaline, but in another aspect, it also has the property of forming a complex with a metal ion. For this reason, it is thought that a part of ammonia coordinates to titanium ions or metal ions.

In the next step (third step; step S130), the reaction solution is stirred.
Metal particles grow by stirring the reaction solution. The reaction solution is stirred for several minutes to several hours.

  Although it is considered that the growth of individual metal particles varies, the variation in the particle size of the generated metal particles is small. This is because the growth rate of the metal particles decreases when the particle size becomes a predetermined size or more. That is, it is considered that as the metal particles grow, the dispersant adheres to the surface of the metal particles, and the metal deposition on the surface of the metal particles is suppressed. Moreover, since a dispersing agent adheres to the surface of a metal particle, it suppresses aggregation of metal particles. For this reason, secondary particles or aggregated particles are hardly formed.

  In addition, ammonia gas is generated during the stirring of the reaction solution. The ammonia gas is preferably recovered. Thereby, the recovery rate of ammonia can be increased, and ammonia can be prevented from leaking to the outside.

In the next step (fourth step; step S140), the metal particles are separated from the reaction solution.
The metal particles are separated from the reaction solution by a method such as sedimentation, centrifugation, and filtration. When the metal particles are ferromagnetic, the metal particles may be collected by a magnet. For example, when nickel, iron, or cobalt is contained in the metal particles, the metal particles are collected using a magnet.

In the next step (fifth step; step S150), ammonia is recovered from the reaction solution.
Ammonia is recovered by heating the reaction solution. That is, the reaction solution is heated, and the ammonia gas generated thereby is recovered by an ammonia recovery device. And in order to reuse ammonia at a 2nd process, ammonia is stored in a storage tank.

  Examples of the ammonia recovery device include a water flow type scrubber and a compression liquefaction device. In addition, the apparatus employ | adopted as an ammonia collection | recovery apparatus is not limited to these. Any device that can recover and reuse ammonia can be used. For example, a method of adsorbing ammonia on an adsorbent (for example, zeolite) and desorbing ammonia by heating the adsorbent is also conceivable.

  In a water flow type scrubber, ammonia is recovered by dissolving ammonia in water. In this case, ammonia is stored in a state dissolved in water. When reusing ammonia, the water stored in the ammonia recovery device (water containing ammonia) is heated to turn ammonia into gas (ammonia gas), and ammonia is taken out from the solution.

  In the compression liquefaction device, the gas discharged from the reaction solution is compressed with a compressor, and the ammonia is further cooled with a cooling device. In this case, ammonia is liquefied and stored. When reusing ammonia, it is used as ammonia gas by heating liquid ammonia.

  Ammonia does not directly participate in the oxidation-reduction reaction during the precipitation of metal particles. Ammonia is hardly decomposed by the oxidation-reduction reaction. For this reason, 60 to 80% of the amount added when the reaction solution is made alkaline in the second step can be recovered in this step.

In the next process (sixth process step S160), the reaction solution is subjected to electrolytic treatment.
The concentration of tetravalent titanium ions in the reaction solution is high. Therefore, in order to recycle the reaction solution, the tetravalent titanium ions are reduced to increase the concentration of the trivalent titanium ions.

  Tetravalent titanium ions are likely to be reduced when acidic. For this reason, the reaction solution is acidified, and the reaction solution is circulated to the cathode side of the electrolysis apparatus for electrolysis. According to the electrolytic treatment, 95% or more (molar ratio) of titanium ions in the solution can be converted to trivalent titanium ions.

The electrolytically treated reaction solution is reused for the next generation of metal particles.
That is, in the second production of metal particles, a reaction solution is prepared using an electrolytically treated reaction solution. And the process similar to the production | generation process of the 1st metal particle is performed, and a metal particle is produced | generated. In the subsequent production of metal particles, the reaction solution used in the past is similarly regenerated and used. That is, the reaction solution containing titanium ions is repeatedly used in the production of metal particles.

  In the following description, the production process of the metal particles is completed (that is, the metal particles are generated through the processes from the first process to the sixth process) as “one-time production of metal particles”. Call it.

The effect | action in the manufacturing method of such a metal particle is demonstrated compared with the conventional manufacturing method.
The conventional manufacturing method has the same steps as the steps from the first step to the fourth step shown in the present embodiment. However, the pH adjuster used when making the reaction solution alkaline is not particularly limited. For this reason, conventionally, sodium carbonate, which is easy to handle, is preferably used. Moreover, in the conventional manufacturing method, the pH adjuster is not collect | recovered.

  That is, in the conventional manufacturing method, the pH adjuster thrown in by one production of metal particles is not reused. For this reason, it is necessary to add a pH adjuster to the reaction solution every time the metal particles are produced. When sodium carbonate is used as the pH adjuster, the concentration of sodium ions in the reaction solution increases as a result of regenerating and repeatedly using the reaction solution. As a result, the formation of a metal ion complex is inhibited, and the variation in the particle size of the metal particles is increased. Moreover, as a result of the high concentration of sodium ions, the reaction solution cannot be recycled.

  The same situation occurs when ammonia is used as the pH adjuster. That is, as a result of regenerating and repeatedly using the reaction solution, the concentration of ammonia in the reaction solution increases, and as a result, the variation in the particle size of the metal particles increases.

  Moreover, in the conventional manufacturing method, since a pH adjuster is consumed in the production of metal particles, it is necessary to store a large amount of the pH adjuster as a raw material. In particular, when ammonia is used for pH adjustment, it is necessary to handle it as a dangerous substance, and therefore, there is a problem that it takes more time for storage management than sodium carbonate or the like.

  In contrast, in the method for producing metal particles of the present embodiment, ammonia is used as a pH adjuster, and ammonia is separated from the reaction solution and recovered in the fifth step of the production process. The recovered ammonia is reused as a pH adjuster.

  That is, since it has the process of isolate | separating ammonia from a reaction solution, it is suppressed that ammonia concentration becomes high too much. As a result, it is possible to suppress an increase in the variation in the particle diameter of the metal particles due to the high concentration of ammonia. In addition, since the ammonia recovered from the reaction solution is reused, the amount of ammonia used (total amount of use) can be reduced when repeatedly producing metal particles. For this reason, there is also an advantage that the storage amount of ammonia is reduced.

With reference to FIG. 2, an example of the metal particle production | generation apparatus 1 which produces | generates a metal particle is demonstrated.
FIG. 2 shows an example of an apparatus suitable for the production of ferromagnetic metal particles.
When manufacturing ferromagnetic metal particles, the metal particles can be recovered by a magnet. On the other hand, when producing non-magnetic metal particles, the apparatus configuration is different because the metal particles cannot be collected by a magnet.

The metal particle generation apparatus 1 includes a reaction apparatus 10 that generates metal particles and an ammonia recovery apparatus 50 that recovers ammonia.
First, the reaction apparatus 10 will be described.

  The reaction apparatus 10 includes a reaction tank 20 that stores a reaction solution, a stirring device 30 that stirs the reaction solution, a recovery device 25 that recovers metal particles, and a heating device 40 that heats the reaction solution. . The collection device 25 is configured by a magnet or an electromagnet.

The reaction tank 20 is provided with a pH sensor 21 that detects the pH of the reaction solution and a titanium ion sensor 22 that detects the concentration of trivalent titanium ions in the reaction solution.
An ammonia discharge port 27 for discharging ammonia gas is provided at the ceiling of the reaction tank 20. In addition, ammonia gas is mainly generated by stirring the reaction solution (third step) or heating the reaction solution (fifth step).

In the upper part of the reaction tank 20, an inlet 23 for introducing the reaction solution is provided.
In the lower part of the reaction tank 20, there are provided a discharge port 24 for discharging the supernatant of the reaction solution and an ammonia input port 26 for supplying ammonia gas. A first gas pipe 51 through which ammonia gas flows is connected to the ammonia inlet 26.

  The stirring device 30 includes a shaft rod 31 and a stirring blade 32. When stirring the reaction solution, the stirring blade 32 rotates at a predetermined rotational speed. The rotational speed of the stirring blade 32 is controlled in accordance with the amount of metal particles deposited.

The heating device 40 is provided at the bottom of the reaction vessel 20.
The heating device 40 heats the reaction solution to a predetermined temperature when separating ammonia from the reaction solution.

Next, operation | movement of the reaction apparatus 10 is demonstrated along the flow of the manufacturing process of a metal particle.
In the first step, a reaction solution is prepared. This preparation is performed in an apparatus different from the reaction apparatus 10.

In the second step, the pH of the reaction solution is adjusted.
First, the reaction solution prepared in the first step is poured into the reaction tank 20 from the inlet 23.
At this time, the reaction apparatus 10 detects the pH of the reaction solution by the pH sensor 21. Based on the detected pH value and the target pH value (hereinafter, target pH), the amount of ammonia gas to be introduced into the reaction solution is calculated, and ammonia gas is supplied to the reaction tank 20 in accordance with the calculated amount. Further, when the value of the pH sensor 21 approaches the target pH, ammonia water is injected. In the first production of metal particles, the pH may be adjusted only with aqueous ammonia without using ammonia gas.

In the third step, the reaction solution is stirred.
At this time, the reaction device 10 drives the stirring device 30.
The operating time of the stirring device 30, the rotational speed of the stirring blade 32, and the like are controlled according to the concentration change rate of the trivalent titanium ions. For example, when the concentration change rate of the trivalent titanium ions proceeds faster than the set reaction rate, the rotational speed is decreased.

In the fourth step, the metal particles are separated from the reaction solution.
The stirring device 30 is stopped and the metal particles are allowed to settle. Then, when the sedimentation of the metal particles is completed, the metal particles are recovered by the recovery device 25.

In the fifth step, ammonia is recovered.
At this time, the reaction apparatus 10 heats the reaction solution with the heating apparatus 40.
Ammonia gas generated from the reaction solution is guided to the ammonia recovery device 50 through the second gas pipe 52.

Next, the ammonia recovery device 50 will be described.
The ammonia recovery device 50 includes an ammonia recovery tank 53 for dissolving ammonia in water, an ammonia storage tank 54 for storing water containing ammonia (ammonia-containing water), and a heating device 55 for heating the ammonia-containing water.

  The ammonia recovery tank 53 is connected to a second gas pipe 52 that guides ammonia gas discharged from the ammonia discharge port 27 of the reaction tank 20. The ammonia recovery tank 53 has the same structure as the water flow scrubber. That is, the ammonia recovery tank 53 dissolves ammonia in water by causing ammonia gas to flow through the mist of water and bringing water and ammonia gas into contact with each other.

Next, operation | movement of the ammonia collection | recovery apparatus 50 is demonstrated along the flow of the manufacturing process of a metal particle.
In the third step, the reaction solution is stirred. At this time, ammonia gas is generated from the reaction solution. The ammonia gas is sent to the ammonia recovery device 50 through the second gas pipe 52. The ammonia recovery device 50 injects water into ammonia gas. Thereby, ammonia is dissolved in water. This water (containing ammonia) is stored in the ammonia storage tank 54.

Ammonia contained in the ammonia-containing water is used in the second step.
That is, in the second step, ammonia gas is injected into the reaction solution in order to make the reaction solution alkaline. For this purpose, the ammonia-containing water stored in the ammonia storage tank 54 is heated to generate ammonia gas. Then, ammonia gas is supplied to the reaction tank 20 through the first gas pipe 51.

  Referring to FIG. 2, an example of the metal particle generating apparatus 1 suitable for the production of ferromagnetic metal particles is shown. Here, however, the metal particle generating apparatus that can be applied to non-magnetic metal particles is also shown. An example (hereinafter, metal particle generating apparatus 100) is given. The metal particle generating apparatus 100 has a configuration that facilitates recovery of metal particles that are not magnetic. In addition, the same structure as the metal particle production | generation apparatus 1 attaches | subjects the same code | symbol as the metal particle production | generation apparatus 1, and abbreviate | omits the description.

FIG. 3 is a schematic diagram of the metal particle generating apparatus 100.
The metal particle generation apparatus 100 includes a reaction apparatus 10 that generates metal particles, an ammonia recovery apparatus 50 that recovers ammonia, and an ammonia separation apparatus that separates ammonia by storing the supernatant of the reaction solution and heating the supernatant. 110.

  The ammonia separation device 110 includes a storage tank 120 that stores a reaction solution, a stirring device 160 that stirs the reaction solution, and a heating device 140 that heats the reaction solution. The storage tank 120 is connected to the reaction tank 20 of the reaction apparatus 10 by a connecting pipe 180. An ammonia discharge port 130 for discharging ammonia gas is provided at the ceiling of the storage tank 120. A pipe 170 is connected so that ammonia discharged from the ammonia discharge port 130 is guided to the ammonia recovery device 50. A discharge port 150 for discharging the reaction solution from which ammonia has been separated is provided at the bottom of the storage tank 120. On the other hand, the reactor 10 includes the same components (except for the recovery device 25 and the discharge port 24) as those shown in FIG. Furthermore, a discharge port 200 for discharging a suspension containing a precipitate of metal particles is provided in the lower part of the reaction apparatus 10.

Next, the operation of the metal particle generating apparatus 100 will be described.
The operation of the metal particle generating apparatus 100 will be described along the flow of the metal particle manufacturing process.
The operation from the first step to the third step is the same as the operation of the metal particle generating apparatus 1 shown in the above embodiment. That is, the reaction solution is charged into the reaction apparatus 10, and the reaction solution is adjusted to be alkaline and stirred. Next, the metal particles are separated.

The metal particle separation operation is different from that of the metal particle generator 1 of the above embodiment.
Specifically, the stirring device 30 is stopped and the metal particles are allowed to settle. When the settling of the metal particles is completed, a suspension is formed at the bottom of the reaction vessel 20. Therefore, the supernatant of the reaction solution is transferred to the storage tank 120. Thereby, the supernatant liquid and suspension of the reaction solution are separated. The suspension is taken out from the discharge port 200. Thereafter, the metal particles are separated from the suspension by a centrifuge or a filtration device. On the other hand, the supernatant liquid transferred to the storage tank 120 is processed as follows. That is, the supernatant liquid is heated to separate the supernatant liquid (reaction solution) and ammonia. Ammonia is recovered by the ammonia recovery device 50. This step corresponds to the fifth step. According to such a metal particle production | generation apparatus 100, a metal particle can be isolate | separated from a reaction solution irrespective of the presence or absence of the magnetism of a metal particle.

With reference to FIG. 4, the electrolyzer 2 used for regeneration of the reaction solution will be described.
The electrolysis apparatus 2 includes a cathode tank 61 having a cathode 61A, an anode tank 62 having an anode 62A, a first storage tank 63 for storing a reaction solution, and a second storage tank for storing an electrolyte solution to be circulated in the anode tank 62. 64 and a power source 65. The cathode tank 61 and the anode tank 62 are partitioned by an anion exchange membrane 66.

The first storage tank 63 and the cathode tank 61 are connected by two pipes 71 and 72.
The reaction solution circulates in a circulation circuit constituted by the first storage tank 63, the cathode tank 61, and the two pipes 71 and 72.

The second storage tank 64 and the anode tank 62 are connected by two pipes 73 and 74.
The electrolytic solution circulates in a circulation circuit constituted by the second storage tank 64, the anode tank 62, and the two pipes 73 and 74.

The reduction process of the reaction solution by the electrolysis apparatus 2 will be described.
When performing the reduction treatment of the reaction solution, the reaction solution is stored in the first storage tank 63. Then, a pH adjuster is added to the reaction solution to make the reaction solution acidic. As the pH adjuster, sulfuric acid, hydrochloric acid, or nitric acid is used.

  Next, the reaction solution is circulated in a circulation circuit including the cathode tank 61 and the first storage tank 63. At this time, the tetravalent titanium ions are reduced at the cathode 61A and converted into trivalent titanium ions. In addition, hydrogen ions are reduced and hydrogen gas is generated. Hydrogen gas is exhausted from the cathode chamber 61.

In the circulation circuit including the anode tank 62 and the second storage tank 64, the electrolytic solution is circulated. As the electrolytic solution, for example, a sodium sulfate solution is used. In the anode 62A, oxygen is generated mainly by oxidation of hydroxide ions (OH ⁻ ).

The total charge of the solution in the cathode chamber 61 tends to shift to negative due to the reduction reaction. The total charge of the solution in the anode tank 62 tends to shift to positive due to the oxidation reaction. For this reason, anions (A ⁻ ) move from the cathode tank 61 to the anode tank 62 through the anion exchange membrane 66. By performing the electrolysis by circulating the reaction solution in such a circulation circuit, 95% (molar amount) or more of the titanium ions in the reaction solution can be converted into trivalent titanium ions.

[Example]
The generation of nickel particles will be described.
The following (1-1) to (1-6) indicate the first generation of nickel particles.

(2-1) to (2-6) show the second generation of nickel particles.
(1-1) Preparation of reaction solution-To 400 g of pure water, 100 g of ammonium chloride as a complexing agent and 274.5 g of trisodium citrate dihydrate as a complexing agent were added to prepare a solution. The solution was set at 35 ° C. and stirred. Next, 28.5 g of nickel chloride hexahydrate was added to this solution. Further, 240 g of a 20% by mass titanium trichloride solution was added as a reducing agent. Then, 4 g of a dispersant containing a polycarboxylic acid compound (Chukyo Yushi Co., Ltd., Serna D735) was added.

(1-2) Adjustment of pH of reaction solution 185 g of 28% ammonia water was added to adjust the reaction solution to pH 8.8 (35 ° C.).
(1-3) Stirring for 1 hour after stirring of reaction solution and addition of aqueous ammonia.
-Ammonia volatilized during the reaction was recovered by the ammonia recovery device 50.

(1-4) Separation of nickel particles: A magnet was placed under the reaction vessel to precipitate the nickel particles.
-The supernatant liquid was taken out and the suspension containing nickel particles and the reaction solution were separated.
A series of operations of adding pure water to the suspension, stirring and washing, and settling with a magnet was repeated several times. In this way, the nickel particles were washed. Thereafter, moisture was removed by heat drying.
FIG. 5 shows a scanning electron micrograph of nickel particles.
-The nickel particle yield was 92%. The nickel particle yield is calculated by dividing the total amount (molar amount) of nickel particles obtained by this production method by the amount of nickel (molar amount) in the nickel chloride dissolved during the preparation of the reaction solution. Indicates the percentage of the value.

(1-5) Ammonia recovery / reaction solution was heated to 75 ° C., and ammonia gas was recovered by the ammonia recovery device 50. This lowered the pH to 7.5 (room temperature).

(1-6) 50% sulfuric acid was added to the electrolytic treatment / reaction solution to adjust the pH to 4.5, and this solution was injected into the first storage tank 63 of the electrolysis apparatus 2.
-A 10% aqueous sodium sulfate solution was injected into the second storage tank 64 as an electrolytic solution.
-Electricity was supplied between the anode 62A and the cathode 61A, and the electrolytic solution and the reaction solution were circulated in the respective circulation circuits.
-During the reduction treatment, the concentration of trivalent titanium ions was measured by oxidation-reduction titration. Electricity was supplied until the ratio of trivalent titanium in all titanium ions reached 95% or more (molar amount).
-The pH after electrolytic treatment was 5.5.

Next, the second generation of metal particles will be described.
In the second generation of metal particles, a reaction solution obtained by electrolytic treatment of the reaction solution used in the first round (the solution obtained by the electrolytic treatment of (1-6) above) was used. Details will be described below.

(2-1) Preparation of reaction solution-Electroregenerated reaction solution was supplemented with 20 g of ammonium chloride as a complexing agent and 55 g of trisodium citrate dihydrate as a complexing agent. Next, 28.5 g of nickel chloride hexahydrate was added to this solution. Furthermore, 0.8 g of a dispersant containing a polycarboxylic acid compound (Chukyo Yushi Co., Ltd., Serna D735) was supplemented and stirred. During stirring, the temperature of the reaction solution was maintained at 35 ° C. The amount of nickel chloride hexahydrate 28.5 g is equal to the amount added during the first nickel particle generation.

(2-2) Adjustment of pH / Ammonia-containing water stored in the ammonia recovery device 50 was heated to 80 ° C. to generate ammonia gas, and ammonia gas was bubbled into the reaction solution. Thereby, the pH of the reaction solution was raised to 8.5. Immediately after this, 28% aqueous ammonia was added to adjust the pH to 8.8. The added 28% ammonia water was 45 g. This amount corresponds to about 24% of the amount of ammonia water added at the first generation of metal particles.

(2-3) Stirring of the reaction solution / After adding ammonia water, stirring was performed for 1 hour.
-Ammonia volatilized during the reaction was recovered by the ammonia recovery device 50.
(2-4) Separation of nickel particles / Separation of nickel particles was performed in the same manner as the first nickel particles.
-The nickel particle yield was 91%.
FIG. 6 shows a scanning electron micrograph of nickel particles.

(2-4) Ammonia recovery / ammonia recovery was performed in the same manner as in the first generation of nickel particles.
(2-6) Electrolytic treatment / electrolytic treatment was performed in the same manner as in the first generation of nickel particles.

The first generation of nickel particles is compared with the second generation of nickel particles.
First, the following is shown.
The nickel particle yield in the first generation of nickel particles is substantially the same as the nickel particle yield in the second generation of nickel particles. Further, as shown in the photographs of the nickel particles in FIGS. 5 and 6, the average particle size of the first and second metal particles is substantially the same, and the variation in the average particle size is also substantially the same.

  That is, according to the method for producing metal particles of the present embodiment, it can be seen that the reaction solution can be regenerated and reused. Specifically, the reuse of the reaction solution has little influence on the variation in the nickel particle yield, the average particle diameter of the nickel particles, and the average particle diameter of the nickel particles.

Second, the following is shown.
The amount of ammonia replenished for the second generation of nickel particles is 24% by mass of the amount of ammonia used for the first generation of nickel particles. 76% by mass of ammonia is reused. That is, according to the manufacturing method of the metal particle of this embodiment, ammonia consumption can be reduced.

According to the present embodiment, the following effects can be obtained.
(1) The method for producing metal particles of the present embodiment includes a step of preparing a reaction solution, a step of adding ammonia as a pH adjuster to the reaction solution to make the reaction solution alkaline, and stirring the reaction solution, A step of separating metal particles from the solution, and a step of separating ammonia from the reaction solution by heating to recover ammonia. The recovered ammonia is reused as a pH adjuster.

  In this configuration, ammonia is employed as a pH adjuster when making the reaction solution alkaline. Since ammonia becomes a gas (ammonia gas) by heating, it is possible to easily separate ammonia from the reaction solution. For this reason, compared with the case where sodium carbonate etc. are employ | adopted as an alkali pH adjuster, a pH adjuster can be collect | recovered by a simple method and efficiently.

  Further, the recovered ammonia is reused as a pH adjuster. For this reason, compared with the case where ammonia is not reused, the amount of the pH adjusting agent for making the reaction solution alkaline can be reduced in the method for producing metal particles.

  (2) In the method for producing metal particles of the present embodiment, not only recovered ammonia but also ammonia water is used as a pH adjuster. That is, with only the recovered ammonia, the pH value of the reaction solution cannot be set to a predetermined value, and the amount of ammonia may be insufficient. Therefore, occurrence of such a situation can be suppressed. Further, by using ammonia water as the replenishing ammonia, the pH of the reaction solution can be rapidly increased to a predetermined value as compared with the case of using ammonia gas for replenishment.

(3) In the method for producing metal particles of this embodiment, the reaction solution from which the metal particles are separated is acidified, electrolyzed, and the reaction solution is regenerated as a solution containing trivalent titanium ions.
In the second step of the metal particle production process, the reaction solution is made alkaline. At this time, the metal ions are reduced, and the trivalent titanium ions are oxidized to become tetravalent titanium ions. Therefore, in the present invention, in order to reuse this reaction solution, the reaction solution is acidified and then electrolyzed to reduce tetravalent titanium ions. Since the reduction rate of titanium ions is increased by making the reaction solution acidic, the ratio of trivalent titanium ions to the total amount of titanium ions is increased. That is, the regeneration rate of titanium ions is increased. For this reason, the yield in the manufacturing method of a metal particle can be made substantially constant.

(4) In the method for producing metal particles of this embodiment, ammonia is recovered by bringing ammonia into contact with water.
Examples of the ammonia recovery method include a compression method and a cooling method. In this embodiment, ammonia is recovered by contacting with water. According to this method, since facilities such as a compressor and a cooler are unnecessary, it is possible to recover ammonia with simple facilities as compared with the compression method and the cooling method.

  (5) In the method for producing metal particles of the present embodiment, the reaction solution contains at least one complex selected from the group consisting of ammonium chloride, trisodium citrate, sodium tartrate, sodium acetate, and gluconic acid. Include agent. These complexing agents form complexes with metal ions and titanium ions, and slow the redox reaction rate of both. That is, with this configuration, the growth of the metal particles can be made slow and the particle diameter can be reduced compared with the case where the complexing agent is not present in the reaction solution.

  (6) In this embodiment, the reaction solution contains at least one dispersant selected from the group consisting of polycarboxylic acid, polyacrylic acid, polyvinyl alcohol, polyvinyl pyrrolidone, and polyethyleneimine. These dispersants suppress the growth of metal particles precipitated in the reaction solution and suppress the aggregation of the metal particles. That is, it has a function of inhibiting the formation of secondary particles or aggregates. For this reason, it can suppress that a metal particle becomes large too much and formation of a secondary particle or an aggregated particle by including a dispersing agent in a reaction solution. Therefore, with this configuration, variation in the average particle diameter of the metal particles can be reduced.

(Modification)
In addition, the embodiment of the present invention is not limited to the above-described embodiment, and can be implemented by changing it as shown below, for example.

  -The order of the manufacturing process of the metal particle in an Example is as follows. That is, preparation of the reaction solution, pH adjustment (alkalization) of the reaction solution, separation of metal particles, recovery of ammonia, and electrolytic treatment of the reaction solution are performed in this order. On the other hand, instead of the order of such steps, reaction solution preparation, pH adjustment of the reaction solution, recovery of ammonia, separation of metal particles, and electrolytic treatment of the reaction solution can be performed. That is, ammonia may be recovered before the metal particles are separated, and the recovered ammonia may be reused as a pH adjuster. Even in this case, the amount of the pH adjusting agent for making the reaction solution alkaline can be reduced as compared with the case where the ammonia is not reused.

  -Although the Example has given the example of the manufacturing method of nickel particle | grains, application of this invention is not limited to the manufacturing method of nickel particle | grains. That is, the present invention also relates to a metal particle having a composition of at least one selected from the group consisting of tungsten, tantalum, rhenium, iron, cobalt, nickel, copper, silver, gold, and platinum. The invention can be applied. Moreover, the effect of said (1)-(6) can be acquired by the application.

  -In an Example, although ammonia gas and ammonia water are used in order to make a reaction solution alkaline in the 2nd process of manufacture of a metal particle, it does not prevent using basic substances other than ammonia. For example, a small amount of sodium carbonate may be added.

  In the example, ammonia gas and aqueous ammonia are used to make the reaction solution alkaline in the second step of producing the metal particles, but the pH of the reaction solution may be adjusted only with ammonia gas. By increasing the purity of the ammonia gas, the rate of increase in pH can be increased.

  In the example, ammonia gas and aqueous ammonia are used to make the reaction solution alkaline in the second step of producing the metal particles, but the pH of the reaction solution may be adjusted only with aqueous ammonia. As the ammonia water, ammonia water containing water stored in the ammonia storage tank 54 of the ammonia recovery device 50 can be used. In this case, it is preferable to adjust the concentration of ammonia.

  DESCRIPTION OF SYMBOLS 1 ... Metal particle production | generation apparatus, 2 ... Electrolysis apparatus, 10 ... Reaction apparatus, 20 ... Reaction tank, 21 ... pH sensor, 22 ... Titanium ion sensor, 23 ... Input port, 24 ... Discharge port, 25 ... Recovery apparatus, 26 ... Ammonia inlet, 27 ... ammonia outlet, 30 ... stirring device, 31 ... shaft bar, 32 ... stirring blade, 40 ... heating device, 50 ... ammonia recovery device, 51 ... first gas pipe, 52 ... second gas pipe, 53 ... Ammonia recovery tank, 54 ... Ammonia storage tank, 55 ... Heating device, 61 ... Cathode tank, 61A ... Cathode, 62 ... Anode tank, 62A ... Anode, 63 ... First storage tank, 64 ... Second storage tank, 65 ... Power supply 66 ... Anion exchange membrane 71,72,73,74,170 ... Piping 100 ... Metal particle generator 110 ... Ammonia separator 120 ... Storage tank 130 ... Ammonia outlet 140 ... Heating device 150 ... outlet, 160 ... stirrer, 180 ... connection pipe, 200 ... discharge port.

Claims (6)

In a method for producing metal particles, wherein metal particles are generated by reducing the metal ions in a solution containing trivalent titanium ions and metal ions,
Preparing a reaction solution containing metal ions reduced by trivalent titanium ions and trivalent titanium ions;
adding ammonia as a pH adjusting agent to the reaction solution to make the reaction solution alkaline, and stirring the reaction solution;
Separating metal particles from the reaction solution;
Separating ammonia from the reaction solution by heating, and recovering the ammonia,
The method for producing metal particles, wherein the recovered ammonia is reused as the pH adjusting agent. In the manufacturing method of the metal particle of Claim 1,
The recovered ammonia and aqueous ammonia are used as the pH adjuster. A method for producing metal particles, wherein: In the manufacturing method of the metal particle of Claim 1 or 2,
The method for producing metal particles, wherein the reaction solution from which the metal particles have been separated is acidified, electrolyzed, and the reaction solution is regenerated as a solution containing trivalent titanium ions. In the manufacturing method of the metal particle as described in any one of Claims 1-3,
A method for producing metal particles, characterized in that, in the step of separating ammonia from the reaction solution by heating and recovering the ammonia, ammonia is recovered by bringing the ammonia generated by heating the reaction solution into contact with water. In the manufacturing method of the metal particle as described in any one of Claims 1-4,
The reaction solution contains at least one complexing agent selected from the group consisting of ammonium chloride, trisodium citrate, sodium tartrate, sodium acetate, and gluconic acid. . In the manufacturing method of the metal particle as described in any one of Claims 1-5,
The said reaction solution contains the at least 1 sort (s) of dispersing agent selected from the group comprised by polycarboxylic acid, polyacrylic acid, polyvinyl alcohol, polyvinylpyrrolidone, and polyethyleneimine. The manufacturing method of the metal particle characterized by the above-mentioned.