JPWO2009014165A1 - Method for concentrating colloidal dispersion - Google Patents

Abstract

A method for concentrating a colloidal dispersion by applying a potential gradient to the colloidal dispersion, wherein the apparatus for concentration has a concentrating container for concentrating by immersing the anode and cathode in the colloidal dispersion and has a separation membrane. This is a method for concentrating a colloidal dispersion characterized by not. It is possible to provide a method for concentrating a colloidal dispersion that can be concentrated at a high concentration rate using a small and low energy consumption device without using a separation membrane.

Description

  The present invention relates to a method for concentrating a colloidal dispersion.

In general, as a method of concentrating a colloidal dispersion such as a noble metal colloidal dispersion, a method of concentrating the colloidal dispersion by evaporating water in the colloidal dispersion by heating (hereinafter referred to as “evaporation method”) is known. (For example, refer to Patent Document 1). However, problems such as aggregation of colloidal particles occur when heating at a high temperature. For example, in Patent Document 1, a time of about 15 minutes to 240 minutes at a temperature of about 50 to 90 ° C. under normal pressure or reduced pressure. Has been proposed (see Patent Document 1 [0018]).
However, this evaporation method is inherently accompanied by heating even under mild heating conditions, and may cause alterations such as oxidation and aggregation of the noble metal colloid. In addition, there are problems in that the cost of fuel and electric power for heating and the cost of equipment such as a decompression equipment and a steam recovery cooling device arise, resulting in an increase in manufacturing cost.

As a concentration method that does not involve heating, a method of concentrating an aqueous solution containing an insoluble component such as a solid suspension or a colloid using an osmotic membrane has been proposed (see, for example, Patent Document 2). Patent Document 2 discloses the following concentration method.
That is, the container is divided into two with a semipermeable membrane, and a solution containing an insoluble component such as a solid suspension or colloid to be concentrated (hereinafter referred to as “low osmotic pressure solution”) is placed in one of the containers. A solution adjusted to have a higher osmotic pressure than the low osmotic pressure solution (hereinafter referred to as “high osmotic pressure solution”) is placed on the other side. Thereafter, since the solvent component moves from the low osmotic pressure solution to the high osmotic pressure solution through the osmotic membrane, the concentration of the insoluble component in the low osmotic pressure solution is increased, and as a result, the low osmotic pressure solution is concentrated. It is a method of being done.
However, the method using an osmotic membrane generally has a problem that the processing time is long. Specifically, in the example of Patent Document 2, it takes 12 hours to concentrate milk by 1.5 times using a sodium chloride aqueous solution as a hyperosmotic solution (see Patent Document 2, Example 1). ), 15 hours are required to concentrate the cutting oil drainage (see Patent Document 2 and Example 2). Further, there is a problem in that the solute of the high osmotic pressure solution may be mixed into the solution to be treated.

  In contrast to these methods, there is a method of applying a potential gradient to the colloidal dispersion and concentrating using a phenomenon in which the colloid moves near the electrode depending on the charged state of the colloid. In this case, a concentration gradient occurs in the same direction as the potential gradient. That is, the positively charged colloidal particles gather on the negative electrode side, and the negatively charged colloidal particles gather on the positive electrode side (see, for example, Non-Patent Document 1 and Non-Patent Document 2). The potential gradient is obtained by dividing the applied voltage applied to the electrodes by the distance between the electrodes.

In addition, from the viewpoint of production efficiency, a method for continuously concentrating a colloidal dispersion is desired. However, various methods have been proposed as a method for continuously concentrating a colloidal dispersion. For example, colloidal dispersion by ultrafiltration is proposed. A method for continuously concentrating a dispersion is known (see Patent Documents 3 [0087] and [0102]). Ultrafiltration is a general filtration method that separates water and particles by a filter, and uses a filtration membrane with controlled pores, and drains the solvent by the pressure difference through the filtration membrane and concentrates it. is there. With this method, even minute colloidal particles can be concentrated.
However, the method using ultrafiltration has a problem that it is necessary to exchange the filtration membrane to be used according to the size of the colloidal particles, and the work is complicated. Further, since the concentration ratio cannot be increased and the concentration ratio is usually about 2 to 3 times, a plurality of concentration steps are required to obtain a high concentration colloidal dispersion. Furthermore, since it is necessary to apply a pressure of 0.1 to 1 MPa during filtration, there is a problem that the apparatus is enlarged even when a small amount of concentration is performed.

As a method for continuously concentrating a colloidal dispersion, a method using an ultrafiltration device and an electrodialysis device has been proposed (see Patent Document 4, Claim 3, and [0021]). This concentrates in a short time by combining ultrafiltration with electrodialysis using an ion exchange membrane.
An ion exchange membrane is a porous membrane having a charge, and has the property of allowing only cations or anions to pass through. In the electrodialysis method, the ion components dissolved in water are concentrated by combining the ion exchange membranes. The driving force in this concentration method is the amount of electricity, and ions in water can be concentrated in proportion to the amount of electricity added. Therefore, the concentration ratio is higher than that of the concentration method using pressure-driven membrane separation such as reverse osmosis.
However, since electrodialysis is concentrated by a combination of electrophoresis and a cation exchange membrane and an anion exchange membrane, it is necessary to select the cation exchange membrane to be used and the colloidal material that concentrates the anion exchange membrane. There is a problem that is complicated. In addition, since a large ion conductive current (several A to 10 A at 30 to 40 V) must be flowed during the concentration process, the device itself can be reduced in size, but the power supply device requires a very large device and consumes a large amount of energy. There was also a problem.

JP 2005-169333 A JP-A-9-75677 JP 2002-83518 A JP-A-8-278580 Tamotsu Kondo et al. “Easy Colloids and Interface Science” 21-25 (1983, Sankyo Publishing) Katsuichi Ikeda "Basic Chemistry Selection 22 Colloid Chemistry" 117-121 (1986, Saika Huafusa)

  Under such circumstances, an object of the present invention is to provide a method for concentrating a colloidal dispersion that can be concentrated at a high concentration rate using a small and low energy consumption device without using a separation membrane. .

In the course of research on the technology for supporting noble metal colloid particles having no protective colloid on a substrate by electrodeposition, a potential gradient is applied to a dispersion of charged fine particles such as a colloid dispersion under specific conditions. It has been found that the fine particles move in a direction perpendicular to the free plane (gravity direction), which does not necessarily match the potential gradient, contrary to conventional common general knowledge. That is, as described above, generally, when a potential gradient is applied to a colloidal dispersion, positively charged colloidal particles gather on the negative electrode side, and negatively charged colloidal particles gather on the positive electrode. By controlling the amount of current, such as the ion concentration, the fine particles such as negatively charged noble metal colloid particles hardly cause electrodeposition on the positive electrode, and the high-concentration part and the dilute part in the dispersion so as to move away from the negative electrode It was found that the phenomenon of separation occurs.
Although the details of the mechanism by which this phenomenon occurs are unknown, the present inventors based on this finding, have concentrated on a colloid having a charge, such as a noble metal colloid dispersion, by a method that is essentially not accompanied by heating. completed.
In addition, in the above-described method for concentrating a colloidal dispersion, the present inventors have used a concentrating container having a specific structure, and further a replenishing container for continuously replenishing the colloidal dispersion, so that the colloid can be obtained without using a separation membrane. It has been found that the dispersion can be concentrated efficiently. The present invention has been completed based on such findings.

That is, the present invention
(1) A method for concentrating a colloidal dispersion by applying a potential gradient to the colloidal dispersion, wherein the apparatus for concentration has a concentration container for concentrating by immersing the anode and cathode in the colloidal dispersion, A method for concentrating a colloidal dispersion, characterized by not having
(2) The electrode having the same sign as that of the charge of the colloid is disposed relatively close to the surface of the colloidal dispersion, and the electrode having a different sign is disposed relatively close to the bottom of the concentration vessel. A method for concentrating the colloidal dispersion,
(3) Further, a replenishing container for continuously replenishing the colloidal dispersion is provided, the concentrating container and the replenishing container are connected by an opening of the concentrating container, and the opening is filled with the colloidal dispersion. The method for concentrating a colloidal dispersion according to (1) or (2) above,
(4) The colloid dispersion liquid in the concentration container has a colloid highly concentrated region and a defect region, and the colloid dispersion liquid continuously replenished from the replenishment container is supplied to the colloid highly concentrated region. The method for concentrating the colloidal dispersion according to (3),
(5) The composition and composition ratio constituting the colloid are the same as the composition and composition ratio of the material constituting the anode and cathode, or the material constituting the anode and cathode is an electrochemically inert material with respect to the colloid. A method for concentrating a colloidal dispersion according to any one of (1) to (4) above,
(6) The method for concentrating a colloidal dispersion according to any one of (1) to (5) above, wherein the concentration container is made of an insulating material,
(7) The method for concentrating a colloidal dispersion according to any one of (3) to (6) above, wherein the replenishing container is made of an insulating material, and (8) the above (1), wherein the colloid is a noble metal colloid. A method for concentrating the colloidal dispersion according to any one of to (7),
Is to provide.

  According to the present invention, a colloidal dispersion can be concentrated at a high concentration rate using a small apparatus with low energy consumption without using a separation membrane.

It is explanatory drawing of the concentration method of a colloid dispersion liquid. It is explanatory drawing which shows the isolation | separation state of the colloid dispersion liquid after a voltage application. It is a schematic diagram which shows the structure of the container which isolate | separates and collects a high concentration area | region. It is a schematic diagram which shows the structure of the container which isolate | separates a thin area | region and isolate | separates and collects a high concentration area | region. It is explanatory drawing of the concentration method of a colloid dispersion liquid.

Explanation of symbols

1 Colloidal dispersion (before voltage application)
10 Colloidal dispersion (defect area)
11 Concentration tank 12 Anode 13 Cathode 14 Power supply (DC power supply)
14 'conductor 15 dispersion interface 16 colloid dispersion (high concentration region)
17 Replenishment tank 18 Replenishment colloid dispersion 19 Opening (connection between the concentration tank and the replenishment tank)
21 Discharge valve (near container bottom)
22 Discharge valve (near electrode bottom)

The method for concentrating a colloidal dispersion according to the present invention is a method for concentrating a colloidal dispersion that imparts a potential gradient to the colloidal dispersion, wherein the concentration device immerses and concentrates the anode and cathode in the colloidal dispersion. It has a container and has no separation membrane.
The colloid in the colloidal dispersion of the present invention is present in an insulating dispersion medium such as pure water without being aggregated microscopically due to electrical repulsion. However, it is loosely surrounded by monoatomic ions with the opposite charge of colloidal particles, and as a whole is electrically neutral. In the present invention, an anode and a cathode are immersed in these colloidal dispersions, and concentrated by applying a potential gradient.

Usually, when an electrode is immersed in a dispersion of charged fine particles to apply a potential gradient, positively charged fine particles gather on the negative electrode side, and negatively charged fine particles gather on the positive electrode side. However, under certain conditions, charged fine particles do not undergo such migration and are concentrated in the direction of gravity (downward) with respect to the electrode.
More specifically, when a constant DC voltage is applied between the electrodes in the concentration container, the colloid is uniformly concentrated near the bottom of the container, resulting in a highly concentrated region of colloid and a defect region from which the colloid has been removed. . At this time, almost no current flows. Specifically, it is 1 mA or less with respect to an applied voltage of several tens of volts (V). Here, colloidal particles and the oppositely charged ions that surround them act together and do not undergo electrolysis. In addition, when a current of 1 mA or more flows, electrolysis of a dispersion medium such as water occurs, which results in preventing colloid concentration.
There are various methods for causing such concentration, such as a method for specifying the positional relationship of the electrodes, a method for setting the conditions of the colloidal solution when applying a potential gradient, and a control of the flowing current. There are ways to do it.

As a method for specifying the position of the electrode, there is a method in which an electrode having the same sign as the charge of the colloid is relatively close to the surface of the dispersion and an electrode having a different sign is relatively close to the bottom of the container.
When the colloid is negatively charged, that is, when the charge of the colloid is negative, the electrode having the same sign, that is, the negative electrode is placed relatively near the dispersion surface of the colloid dispersion, The positive electrode, which is an electrode having a different sign from that of the electric charge, is disposed relatively near the bottom of the container.

Also, the concentrated colloidal dispersion is extracted and the same amount of unconcentrated colloidal dispersion is supplied, or the concentrated colloidal dispersion is supplied to the concentrated colloidal region and is equivalent to the amount of colloid supplied. By collecting a concentrated colloidal dispersion, a concentrated colloid can be obtained continuously.
In a more preferred embodiment, the apparatus for concentration has a concentration container for concentrating by immersing the anode and cathode in the colloidal dispersion, and a replenishing container for continuously replenishing the colloidal dispersion, and these containers are The concentrating container is connected at the opening, and the opening is filled with the colloidal dispersion.

The concentrating container is connected to a replenishing container that continuously replenishes the colloidal dispersion liquid through the opening, and the concentrated colloidal dispersion liquid and the dispersion medium in the defect region corresponding to the concentration degree are extracted, and the same amount as the sum of them. By supplying this unconcentrated colloidal dispersion, the colloidal dispersion can be efficiently concentrated without a separation membrane. Alternatively, a concentrated colloid can be obtained continuously and efficiently by supplying an unconcentrated colloidal dispersion to a high concentration region and collecting a concentrated colloidal dispersion equivalent to the amount of colloid supplied. At this time, the dispersion medium corresponding to the amount of the dispersion medium supplied is removed. In particular, the latter embodiment in which the colloidal dispersion continuously replenished from the replenishing container is supplied to the high concentration region of the colloid is preferable.
In addition, the concentration container and the replenishment container are preferably made of a transparent insulating material from the viewpoint of maintaining the electrical insulation of the colloidal dispersion and from the viewpoint of observing the state of concentration. Specific examples include materials such as glass.

The mechanism by which the colloidal dispersion is concentrated by the above method is considered as follows. That is, in an insulating dispersion medium such as pure water, for example, when the colloid is negatively charged, by applying a DC voltage between the electrodes, the colloid is slightly emitted by the electrons emitted from the cathode. Repelled and the colloidal defect area gradually spreads from the vicinity of the cathode. The interface between the defect region and the high-concentration region thus formed moves so as to reduce the surface energy, and the interface becomes smooth and widens. Once the interface between the high-concentration region and the defect region spreads in the container, negative charges, which are electrons emitted from the cathode, are uniformly distributed on the surface of the insulating dispersion medium, Since an equal amount of positive charge is induced at the interface, the electrical interface is considered to be formed horizontally. In this way, an interface in which the concentration of the colloid changes sharply is formed and separated into a defect region and a high concentration region. Moreover, the colloid has a uniform distribution in the high concentration region.
In addition, as described above, when the unconcentrated colloidal dispersion flows into the high concentration region, the colloid is maintained in the high concentration region while moving the interface, so that the colloid is maintained in the high concentration region, and only the insulating dispersion medium is retained. Therefore, a concentrated colloidal dispersion is continuously obtained.
Accordingly, the colloid concentration in the high concentration region can be controlled by determining the distance between the electrode near the bottom of the vessel and the bottom of the vessel and determining the bulk height of the high concentration region.

Moreover, about the density | concentration of the colloid dispersion liquid added continuously, it is desirable that it is the range of 50-500 mg / L. Within this range, the colloidal dispersion is effectively concentrated.
In the case of continuously concentrating the colloidal dispersion liquid as described above, if the concentration is 50 mg / L or more, the amount of the dispersion medium added additionally does not increase too much, so the high concentration region and the defect region (dilute region). Therefore, the continuous interface is effectively concentrated. From the above viewpoint, the concentration of the unconcentrated colloidal dispersion added later is more preferably in the range of 60 to 150 mg / L.

Next, the conditions for preventing the current from substantially flowing through the colloidal dispersion and enabling the concentration of the colloid include the following.
The average particle diameter of the colloid is preferably in the range of an average particle diameter of 1 to 200 nm.
The temperature of the colloidal dispersion is preferably 40 ° C. or lower. By setting the temperature to 40 ° C. or less, the influence of the thermal diffusion of the colloid in the colloidal dispersion is reduced, and the colloidal dispersion is concentrated. The temperature of the colloidal dispersion is preferably as low as possible while maintaining the liquid state of the colloidal solution, for example, the fluid body of the colloidal solution is preferably 25 ° C. or lower.

  In the concentration method of the present invention, the potential gradient is preferably 2 V / cm or more. If it is 2 V / cm or more, sufficient concentration is possible. The upper limit of the potential gradient is usually about 50 V / cm because electrons emitted from the negative electrode disturb the interface.

  The dispersion medium in the method of the present invention needs to have insulating properties. Specifically, the resistivity is preferably 7 MΩcm or more. When the resistivity is less than 7 MΩcm, an electric current flows through the dispersion medium and an electrolysis phenomenon occurs, so that an initial interface formation phenomenon does not appear. Specifically, pure water can be suitably used.

  For colloids that can be concentrated according to the present invention, noble metals include platinum, ruthenium, palladium, rhodium, rhenium, osmium, gold, iridium, silver and the like. These noble metals may be used alone or in combination of two or more. For example, the concentration method of the present invention is suitably applied to a colloidal dispersion composed of an alloy colloidal particle composed of two or more kinds of noble metal elements or a noble metal colloid particle having a core / shell structure in which two or more kinds of noble metal element layers overlap. used.

  In addition, the method of the present invention can be used which does not substantially contain a protective colloid-forming agent. Here, the protective colloid-forming agent is a substance that is conventionally contained in a colloid liquid in order to maintain the dispersion stability of the colloidal particles, and adheres to the surface of the colloidal particles to form a protective colloid. Examples of such a protective colloid-forming agent include water-soluble polymer substances such as polyvinyl alcohol, polyvinyl pyrrolidone, and gelatin, surfactants, and polymer chelating agents (for example, [0013] in JP-A-2000-279818). And the like).

  In the present invention, the noble metal colloid dispersion without protective colloid is prepared by adding a reducing agent to a solution in which a metal chloride is dissolved and reducing metal ions, as described in the above-mentioned patent document. It can obtain by the method of producing | generating. The noble metal colloid dispersion obtained in this way has good dispersion stability of the noble metal colloid particles even when substantially free of a protective colloid-forming agent, and has a practically sufficient long period, for example, 3 to 30 days. Maintains stable dispersibility.

Next, embodiments of the present invention will be described with reference to the drawings.
In the method of concentrating a colloidal dispersion according to the present invention, as shown in FIG. 1, two electrodes, an anode 12 and a cathode 13, are immersed in the colloidal dispersion 1 in a container 11. A power supply 14 is connected.

  The positions of the anode and the cathode are not particularly limited as long as the effects of the present invention are achieved. However, in order to efficiently concentrate the colloid, the following positional relationship is preferable. In other words, if the colloidal charge is negative, the colloidal charge is controlled so that the lower end of the anode is located at the same position as the lower end of the cathode or below the lower end of the cathode. In this case, it is preferable to control so that the lower end of the cathode is located at the same position as the lower end of the anode or below the lower end of the anode with respect to the direction of gravity.

When a voltage is applied to such an electrode, the colloid in the vicinity where the electrode exists moves below the electrode, and as shown in FIG. 2, a dilute region 10 and a high concentration region 16 are formed, and the colloidal dispersion is concentrated. The At this time, the highest position of the high concentration region 16 substantially coincides with the lower end of the electrode 12.
Then, as shown in FIG. 3, the valve 21 is opened to directly separate and collect the high-concentration colloidal dispersion, or as shown in FIG. 4, the valve 22 is opened to separate and collect the diluted dispersion. By doing so, a high concentration colloidal dispersion can be obtained.

Next, FIG. 5 is explanatory drawing which shows the other aspect in the concentration method of the colloid dispersion liquid of this invention. FIG. 5 illustrates a case where the colloid is negatively charged.
In this embodiment, as shown in FIG. 5, two electrodes, an anode 12 and a cathode 13, are immersed in the colloidal dispersion 10 in the concentration container 11, and a power supply 14 for applying voltage is connected to these electrodes. Yes. The replenishing container 17 is connected to the concentrating container 11 through the opening 19, and the opening 19 does not have any diaphragm.

Regarding the positions of the anode and the cathode, since the colloid is negatively charged, the cathode 13 is positioned relatively near the dispersion surface, and the anode 12 is positioned relatively near the bottom of the container. The anode and cathode electrodes extend in parallel to the bottom of the concentration vessel 11 in consideration of the flow of the replenishment colloid dispersion liquid added from the replenishment vessel 17 through the opening 19 throughout the concentration vessel 11.
When a voltage is applied to such an electrode, the colloid moves below the anode, and a high concentration region 16 is generated under the anode.

  The concentration container 11 in the present invention is preferably made of an insulating material, that is, an insulating container. The refill container 17 is also preferably made of an insulating material. The opening 19 needs to be in the high concentration region 16. Concentration containers 11 may be arranged in parallel with a common replenishment container 17.

  The electrode used in the method of the present invention is preferably a noble metal material from the viewpoint of poor solubility in a colloidal dispersion, and in particular, the same metal as the colloid material, and further, the composition and composition ratio constituting the colloid, the anode and the cathode It is desirable that the composition and composition ratio of the materials constituting the same are the same. In addition, other materials that are electrochemically inert to the colloid can be used.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by this example.
Example 1
(1) Preparation of platinum colloid dispersion 50 g of 0.8 mass% chloroplatinic acid aqueous solution (H ₂ PtCl ₆ · 6H ₂ O) was diluted with 850 g of pure water, and this solution was heated until reaching 100 ° C. Further, 100 g of a 1.0 mass% aqueous sodium citrate solution was added to this solution and refluxed for 1.5 hours to obtain a platinum colloid dispersion. Further, the platinum colloid dispersion was subjected to ion exchange through an ion exchange resin of an acidic / basic mixture to obtain a platinum colloid dispersion for concentration. This platinum colloid dispersion had a platinum colloid particle concentration of about 130 mg / L and an average colloid particle size of 5.2 nm. The resistivity of pure water as a dispersion medium is 7 to 20 MΩcm, and no protective colloid is used. In addition, the ion concentration of the colloidal dispersion was measured using an ICP method, and the average particle size of the colloid was measured using a particle size measuring device (FPAR-1000 type measuring device manufactured by Otsuka Electronics Co., Ltd.).

(2) Concentration of platinum colloidal dispersion A 3.5 × 1 × 4 cm ³ plastic concentration tank was prepared. Similarly, the colloid inlet is made of 0.5 × 1 × 4 cm ³ plastic, and the opening has a cross section of 1 × 0.3 cm ² and a length of 1 cm. In this concentration tank, 12 mL of the platinum colloidal dispersion was added. A platinum wire having a diameter of 0.3 mm was used as the electrode, and the electrode position was 6 mm from the bottom of the concentration tank, and the cathode was 5 mm from the surface (water surface) of the colloidal dispersion medium.
A 40 V DC voltage (corresponding to a potential gradient of 26 V / cm) was applied between the electrodes at 25 ° C., and a current of 100 to 200 μA flowed. When voltage is applied, the platinum colloid moves downward from the anode, with the lower end position of the anode as a boundary, the lower side is a region where the platinum colloid is present at a high concentration (high concentration region), and the upper side is where the platinum colloid is present. Not separated into transparent defect areas. After the voltage application was started, it was concentrated about 7 times in 5 minutes.
Further, when 2.5 mL of the unconcentrated colloidal dispersion was additionally supplied here, the interface between the high concentration region and the defect region was partially changed, but the concentration region immediately recovered and the concentration was maintained. On the other hand, even if the colloidal dispersion in the concentrated region was partially removed with a dropper, the concentrated region was recovered immediately and the concentration was maintained.

Example 2
(1) Preparation of platinum colloid dispersion Platinum colloid dispersion containing protective colloid (TMA (tetramethylammonium hydroxide) surface modified platinum colloid dispersion, commercial product manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., platinum content 10 g / L) was concentrated by the method of the present invention. Distilled water (11.4 mL) was added to the TMA surface-modified platinum colloidal dispersion (0.6 mL) to dilute it 20 times to obtain a sample (500 mg / L).
(2) Concentration of platinum colloidal dispersion A 3 × 1 × 4 cm ³ plastic concentration tank was prepared. Similarly, the colloid inlet is made of 1 × 1 × 4 cm ³ plastic, and the opening has a cross section of 1 × 0.3 cm ² and a length of 1 cm. In this concentration tank, 12 mL of the platinum colloidal dispersion was added. As the electrode, a glass tube other than the tip of a platinum wire having a diameter of 0.3 mm was used. As the electrode position, the anode was positioned 12 mm from the bottom of the concentration tank, and the cathode was the surface of the colloidal dispersion medium (water surface). The position was 3 mm below.
A 40 V DC voltage (corresponding to a potential gradient of 26 V / cm) was applied between the electrodes at 25 ° C. The current immediately after voltage application was 8.5 mA. When a voltage is applied, a dilute region of platinum colloid is generated near the cathode and gradually covers the surface of the concentrating tank (diluted region). After 5 minutes, the upper side of the concentrating tank is the dilute region and the lower end of the anode is the boundary. The lower side became a region (high concentration region) present in a high concentration of platinum colloid. The current at this time was 12 mA, and the height of the interface in a stable state was 5 mm from the bottom of the concentration tank.
After 2 hours of standing in this state, when 2 mL of the above-mentioned 500 mg / L TMA surface-modified platinum colloid dispersion liquid was additionally supplied to the colloid inlet, the interface between the high concentration region and the dilute region temporarily increased, but the interface decreased immediately. After 15 minutes, the height of the interface was 5 mm from the bottom of the concentration tank, and the concentration was maintained.
From this state, when 2 mL of the above-mentioned 500 mg / L TMA surface-modified platinum colloid dispersion liquid at the colloid introduction port was additionally supplied, the interface between the high concentration region and the dilute region temporarily rose, but the interface began to decline immediately, Later, the height of the interface was 5 mm from the bottom of the concentration tank, and the concentration was maintained.
Furthermore, when 4 mL of the diluted region was gently taken out with a dropper and 4 mL of the above-mentioned 500 mg / L TMA surface-modified platinum colloid dispersion liquid was additionally supplied to the colloid inlet, the interface between the high concentration region and the diluted region was disturbed. After 30 minutes, the height of the interface was 5 mm from the bottom of the concentration tank, and it was confirmed that concentration was maintained.
During the voltage application, bubbles were generated from each electrode due to electrolysis of water. In this case, it is considered that both ions did not act together in the process of electric field concentration because the ions having the opposite charge to the colloidal platinum particles are much larger than the monoatomic ions. Therefore, electrolysis occurred and an excessive current flowed, but at the same time, electric field concentration seems to have occurred.
Further, in the vicinity of the surface (water surface) of the colloidal dispersion medium on the anode side, a phenomenon in which unevenness of the colloid concentration (color density by visual observation) occurred and propagated in a wave shape in the solution was confirmed. About this, it is thought that the generation | occurrence | production point of a nonuniformity respond | corresponds with the point where the bubble generated on the anode side reaches the water surface and disappears.
Further, when the temperature of the outer surface of the concentration tank was measured with a non-contact type thermometer, the temperature started to increase immediately after the voltage application (0.3 ° C. per minute) and finally became stable at 35 ° C. On the other hand, the temperature of the surface of the replenishing tank remained at about 29 ° C.

Example 3
(1) Preparation of gold colloid dispersion 9.41 g of a 1% by mass chloroauric acid aqueous solution was diluted with 954.32 g of pure water, and this solution was heated until reaching 100 ° C. Further, 14.4 g of a 0.7% by mass aqueous sodium citrate solution was added to this solution and refluxed for 1 hour to obtain a gold colloid dispersion. Further, the gold colloid dispersion was ion exchanged through an ion exchange resin of an acidic / basic mixture to obtain a gold colloid dispersion for concentration.
(2) Concentration of colloidal gold dispersion 12 mL of colloidal gold dispersion was placed in the same plastic concentration tank as used in Example 2. The same electrode as used in Example 2 was used.
A 40 V DC voltage (corresponding to a potential gradient of 26 V / cm) was applied between the electrodes at 25 ° C. The current immediately after voltage application was 58 μA. By applying voltage, a thin region of colloidal gold is generated near the cathode and gradually covers the surface of the concentration tank (dilute region). After 14 minutes, the upper side of the concentration tank is a thin region, and the vicinity of the lower end of the anode is the boundary. The lower side became a region (high concentration region) present at a high concentration of colloidal gold. The current at this time was 70 μA, and the height of the interface was 15 mm from the bottom of the concentration tank.
In this state, when 2 mL of the gold colloid dispersion liquid was additionally supplied to the colloid introduction port, the interface between the high concentration region and the dilute region temporarily increased, but the interface started to decrease immediately and 24 minutes after the voltage application started. The height of the interface was 10 mm from the bottom of the concentration tank, and concentration was maintained.

  Unlike the electrodialysis, the concentration method of the present invention is a concentration utilizing a change in state due to the formation of an electrical interface and consumes little power, so that a small power source can be used. In addition, since a liquid feeding system that does not use a separation membrane and applies pressure is unnecessary, the pump may be small. Therefore, the apparatus can be downsized as a whole, and the colloid can be concentrated effectively in a short time. Further, even if a dilute colloidal dispersion is added, the interface between the high concentration region and the defect region is maintained, and the colloidal dispersion can be continuously concentrated.

Claims (8)

  A method for concentrating a colloidal dispersion by applying a potential gradient to the colloidal dispersion, wherein the apparatus for concentration has a concentration container for immersing and concentrating the anode and cathode in the colloidal dispersion and has a separation membrane. A method for concentrating a colloidal dispersion characterized by not.   2. The colloid dispersion liquid according to claim 1, wherein an electrode having the same sign as that of the charge of the colloid is relatively close to the surface of the colloid dispersion liquid, and an electrode having a different sign is relatively close to the bottom of the concentration vessel. Concentration method.   And a replenishment container for continuously replenishing the colloidal dispersion, wherein the concentration container and the replenishment container are connected by an opening of the concentration container, and the opening is filled with the colloidal dispersion. Item 3. A method for concentrating a colloidal dispersion according to item 1 or 2.   The colloidal dispersion liquid in the concentration container has a colloidal highly concentrated region and a defect region, and the colloidal dispersion liquid continuously replenished from the replenishing container is supplied to the colloidal highly concentrated region. A method for concentrating a colloidal dispersion as described.   The composition and composition ratio constituting the colloid are the same as the composition and composition ratio of the material constituting the anode and the cathode, or the material constituting the anode and the cathode is an electrochemically inactive material with respect to the colloid. The method for concentrating a colloidal dispersion according to any one of 1 to 4.   The method for concentrating a colloidal dispersion according to any one of claims 1 to 5, wherein the concentration container is made of an insulating material.   The method for concentrating a colloidal dispersion according to any one of claims 3 to 6, wherein the replenishing container is made of an insulating material.   The method for concentrating a colloidal dispersion according to any one of claims 1 to 7, wherein the colloid is a noble metal colloid.

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