JP2011230006A - Method of flocculating dispersed fine particle in liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separation and recovery technique for fine particles, which can be achieved at a low cost without the need of a special additive and without making a structure complicated, and to provide a fine particle flocculation technique in which particularly, a load on an environment is small and which can be used in various scenes in common.SOLUTION: The method of flocculating the fine particles includes: inserting a plurality of electrodes into a liquid to be treated, in which the fine particles are dispersed; and applying voltage between the electrodes so as to have an electric field strength of 0.1-100 V/m.

Description

  The present invention relates to a technique for agglomerating fine particles in a fluid, and more particularly to a method for separating and collecting fine particles with simple equipment by increasing the sedimentation rate of fine particles by applying an ultra-low electric field to the fluid.

  There is a need for technology for homogenizing, separating, and refining fine particles dispersed in water in the production process of industrial wastewater and domestic wastewater, and in the production process of ink, cosmetics, pharmaceuticals, and the like. One of the widely used techniques for removing such fine particles in the water to be treated includes inorganic flocculants such as polyaluminum chloride, aluminum sulfate, polyferric sulfate, polyacrylamide, polydimethyl There is a method in which an organic flocculant such as aminoethyl methacrylate is added to remove the flocculence. In this treatment, particles suspended in water repel each other due to their electric charge on the surface, and they do not settle for a long time. An intermolecular attractive force acts between each other to form an aggregate, which creates a larger aggregate (floc), thereby accelerating the sedimentation speed and facilitating operations such as filtration.

As a technique using a flocculant, for example, an anionic or nonionic organic polymer flocculant is added in a treatment method for polluted water having a suspended solid concentration of 10 kg / m ³ or less to form a floc and pass through a fabric layer. In which the water-soluble organic polymer compound is mixed with the sludge and then treated with a mixture of an insolubilizer and a polymer flocculant that insolubilizes the water-soluble organic polymer compound. There are a method (Patent Document 2) for taking a solid content into a large, strong and highly hydrophobic floc (Patent Document 2), a method using an ion-exchange resin surface having a granular bond structure as an adsorbent (Patent Document 3), and the like. These can improve the filtration efficiency by removing the fine particles that were in a dispersed state after separating them as a lump rather than separating them as they are, but in some cases they require a large amount of flocculant, so in terms of cost Moreover, since the settled floc becomes an aggregate with not only the fine particles to be removed but also the aggregating agent, there may remain a problem in terms of operation such as a large processing amount after separation.

  Examples of not using such a flocculant include those using an adsorbent composed of crystalline fibers of basic magnesium sulfate and magnesium hydroxide (Patent Document 4), As wastewater treatment including fine particles such as cutting wastewater, wastewater containing silicon fine particles discharged by processing a silicon ingot is one that performs high concentration of fine particles by ultrafiltration membranes or microfiltration membranes in multiple stages (Patent Document 5). There are a hollow fiber type filtration means and a centrifugal separation means (Patent Document 6). None of them requires the addition of a flocculant, so the operation is simple, but there are problems in terms of maintenance such as clogging of the filtration membrane.

  In addition, as a method for uniformizing the particle size of organic silicone fine particles used as a raw material for cosmetics and paints, a method of fractionating with a polymer membrane filter (Patent Document 7), useful as a light diffusing agent for liquid crystal display spacers and backlights. A method of discharging a resin melt or solution from a liquid jet head into a liquid or gas insoluble medium in a controlled size in the production process in providing spherical resin particles close to monodisperse with controlled particle size ( Patent Document 8). Since it is not necessary to simply remove the fine particles as in the case of waste liquid treatment, it is necessary to pay close attention to uniformize the particle size of the fine particles.

  Thus, when the fine particles dispersed in the aqueous medium are separated, aggregated, or selected to have a uniform particle size, the cost is reduced, the operation method is simple, and There is a need for technology that does not require special equipment.

JP 62-117694 A Japanese Patent Laid-Open No. 7-999 JP-A-3-232528 JP 2001-246386 A Japanese Patent Laid-Open No. 10-15357 JP 2010-64197 A JP 2006-117867 A JP 2004-300136 A

  An object of the present invention is to provide a technology for separating and collecting fine particles that can be realized at low cost without requiring a special additive or the like and without having a complicated configuration. The purpose is to propose a fine particle agglomeration technique that can be commonly used in various situations.

  As a result of diligent studies to solve the above-mentioned problems and achieve the intended purpose, the fine particles dispersed in water form an electric double layer on the surface and are uniformly dispersed by electrostatic repulsion between the particles. Focusing on the point that it is easy to maintain the state, we found that it would be good to break this state.

  That is, according to the present invention, a plurality of electrodes are inserted into a liquid to be treated in which fine particles are dispersed, and a voltage is applied between the electrodes so that an electric field strength of 0.1 to 100 V / m is obtained. The dispersed fine particles protected by the multi-layer are suspended and aggregated by breaking the electric double layer. Each particle floats in the liquid while repelling each other by the electric double layer, but this is deformed / shrinked by applying voltage, and the intermolecular attractive force (van der Waals force) that is originally working Is considered to be due to the strong action.

  The voltage application time varies depending on conditions such as the type of fine particles to be aggregated and the floating solvent, but a period of about 0.1 to 1000 seconds is preferable. The fine particles agglomerated according to the present invention naturally settle when left standing, but can be positively removed from the solution by passing through a filtration device or the like.

  The method for agglomerating fine particles according to the present invention has a wide range of condition settings depending on the type of liquid to be treated and the type of fine particles, but it is sufficient that the electrode immersed in the solution and electrical connection to it can be secured. A simple method can be proposed at a low cost without requiring complicated equipment. In addition, since the conventional method using a flocculant hardly recovers the flocculant, it was difficult to continuously treat the solution. However, in the present invention, the voltage application to the electrode is extremely simple. It is an operation, easy to process repeatedly, and can be used continuously.

FIG. 1 is a diagram schematically showing an apparatus for measuring the effect of agglomerating fine particles according to the present invention. FIG. 2 is a diagram showing the results according to Example 1 of the present invention. FIG. 3 is a diagram showing the results according to Example 2 of the present invention. FIG. 4 is a diagram showing the results according to Example 3 of the present invention. FIG. 5 is a diagram showing the results according to Example 4 of the present invention. FIG. 6 is a diagram showing the results according to Example 5 of the present invention. FIG. 7 is a diagram showing the results according to Example 6 of the present invention. FIG. 8 is a diagram showing the results according to Example 6 of the present invention. FIG. 9 is a diagram showing the results according to Example 6 of the present invention. FIG. 10 is a diagram showing the results according to Example 6 of the present invention. FIG. 11 is a diagram showing the results according to Example 6 of the present invention.

Hereinafter, preferable conditions and the like related to the aggregation method of the present invention will be described.
The fine particles dispersed in the liquid to be treated form an electric double layer by charge separation occurring at the interface. In the vicinity of the surface, ions having a charge opposite to that of the fine particles gather so that the positively or negatively charged fine particles are electrically neutral. Such ions surround the surface of the fine particle, and the electric double layer is formed by surrounding the layer having the electric charge and the layer having the opposite electric charge. However, the layer of ions in the liquid does not form a region simply and clearly in this way, but the ion concentration of charges opposite to the fine particles is high near the surface of the fine particles, and gradually decreases with increasing distance. Since the ions on the surface of the particles are strongly attracted, this layer is called the fixed layer, the layer where the distribution of both ions gradually becomes uniform is called the diffusion layer, and the fine particles are accompanied by part of the inside of the fixed layer and the diffusion layer. Moving in the liquid. The surface where this movement occurs is called the sliding surface, and the potential of the sliding surface when the potential is measured by defining the potential of a region that is sufficiently away from the fine particles and electrically neutral as zero is called the zeta potential.

  If the absolute value of the zeta potential increases, the repulsive force between the fine particles becomes stronger, so a stable dispersion state is taken in the liquid. If the zeta potential is close to zero, the repulsive force becomes weaker, and the interparticles originally possessed by the fine particles Aggregates easily due to attractive force. In the present invention, by inserting a plurality of electrodes into a liquid in which fine particles are dispersed and applying an extremely low voltage, the electric double layer is displaced and reduced, and as a result, the absolute value of the zeta potential is reduced. I found it. And this phenomenon is used to actively agglomerate fine particles dispersed in the liquid, to separate the fine particles from the liquid, and to select and equalize the size of the fine particles that remain dispersed in the liquid. To do.

  The fine particles targeted by the present invention are inorganic particles such as bentonite, hectorite, kaolin, talc, hydroxyapatite, dolomite, barium sulfate, magnesium oxide, aluminum oxide, titanium oxide, silicone resin, polymethyl methacrylate, polycarbonate, polystyrene Organic particles such as polyethylene, polyacrylstyrene, polyvinyl chloride, melanin resin, polyurethane resin, polyester resin, and the like, which are all fine particles that form an electric double layer in solution. The concentration in these solutions is about 0.000001 to 0.1, preferably about 0.00001 to 0.01, in terms of volume fraction (v / v). When the concentration is lower than the above range, aggregation tends to take time because the number of fine particles present in the range where the intermolecular attractive force of the fine particles acts is small. Further, although the concentration may be higher than the above range, some of them naturally aggregate even if left standing, and the necessity of applying the present invention is low.

  The fine particles become the liquid to be treated of the present invention in a state of being suspended in a solvent. The solvent is generally water, but may be a mixed solution with alcohol or the like, or a treatment solution in which fine particles are dispersed in an alcohol alone solvent. Note that the temperature of the solution during the treatment may be room temperature, and it is not necessary to manage and control the temperature.

  In the present invention, a plurality of electrodes are inserted and used in the liquid to be treated, but the material of the electrodes is not particularly limited, and gold, platinum, silver, aluminum, palladium, copper, zinc, tin oxide, carbonized carbon Commonly used electrode materials such as silicon and graphite can be used. The plurality of electrodes are not necessarily limited to using the same material, and two or more types can be used in combination. Among these electrode materials, platinum is preferable in consideration of pH change of the solution and resistance to various compounds.

  For each electrode, for example, it is most common to dispose two electrodes in the treatment liquid at an interval of 0.1 to 10 mm relative to each other, and the treatment liquid is allowed to flow through the gap, Can be processed continuously. Further, the three electrodes may be arranged so as to occupy the apex position of the triangle, or may be arranged in parallel with the center electrode and the front and rear thereof at an appropriate interval similar to the above. In particular, a preferable arrangement is a comb shape from the viewpoint of increasing efficiency.

  A voltage is applied to the electrode so as to have an electric field strength of 0.1 to 100 V / m. When the electric field strength is less than 0.1 V / m, since the action on the electric double layer is not sufficient, the absolute value of the zeta potential cannot be reduced, and the expression of the fine particle aggregation effect tends to be difficult, and the electric field strength is set to 100 V. Even if it is larger than / m, it does not affect the improvement of the coagulation effect so much, and on the contrary, excess electric energy is consumed, which is not preferable because the cost increases.

  The voltage can be applied by continuously applying a constant voltage, applying a voltage intermittently, or applying a voltage so that the electric field strength changes. Either a direct current or an alternating current power source may be used.

  The voltage application time is 0.1 to 1000 seconds, preferably 1.0 to 600 seconds. If the time is shorter than 0.1 seconds, the effect on the electric double layer is too small to obtain the desired effect of agglomerating the fine particles, and even if the time is longer than 600 seconds, the fine particles are sufficiently aggregated. It is because it may become energized.

The aggregation effect by the fine particle aggregation method of the present invention can be measured by a change in transmitted light intensity of the liquid to be treated as one evaluation method. As long as the fine particles are floating in the liquid to be treated and remain stable, the light transmitted through the liquid to be treated is scattered, the transmitted light intensity is lowered, and the fine particles aggregate and settle to become transparent. This is because the intensity of light transmitted through the liquid to be processed increases. More specifically, in the quartz cell (1) of the spectrophotometer shown in FIG. 1 (having a rectangular parallelepiped space having a height of 45 mm and a capacity of 3.5 ml from a square bottom of 10 mm in length and width) ^Two platinum electrodes (2) having an area of 396 mm ² (length 40 mm, width 9.9 mm) are installed. At this time, the installation place in the cell is arranged along both side walls of the cell so as not to block the transmitted light (3) (therefore, the distance between the electrodes is about 10 mm). And the to-be-processed liquid 10 is inject | poured in a cell to the height of about 25 mm, and it is set as the state where the electrode was immersed in the to-be-processed liquid.

  After injecting the liquid to be processed, the power supply voltage (4) is applied to the electrodes for a predetermined time or at an appropriate interval so that the electric field strength falls within the predetermined range. Measuring the light transmittance of the cell at a wavelength of 540 nm with a spectrophotometer and detecting the change with time of the transmitted light intensity of the liquid to be treated, whereby the fine particles (5) in the liquid to be treated are aggregated and settled Can be observed. In addition, as long as there is no notice in particular, the transmitted light intensity shown in the following examples set a height of about 13.75 mm from the bottom surface of the cell as a temporary measurement position.

  In order to clarify the present invention more specifically, some examples according to the present invention are shown below.

  As a liquid to be treated, 0.0034 g of bentonite particles having a particle size of 2.3 μm were dispersed in 2.3 mL of water. The volume fraction at this time is 0.0005. 2.45 mL of the liquid to be treated is placed in a quartz cell in which a platinum electrode as shown in FIG. 1 is disposed, and an applied electric field is an electric field of direct current or alternating current (50 Hz or 1000 Hz) with an electric field strength of 0.3 V / mm. I applied. The change in transmitted light intensity (%) of the liquid to be treated in this case was measured, and the result is shown in FIG.

  As is clear from FIG. 2, it was not possible to observe that the particles settled when no electric field was applied, whereas according to the method of the present invention, either direct current or alternating current was extremely difficult. It can be seen that the liquid to be treated becomes transparent in a short time. From FIG. 2, it can be seen that the particles agglomerate and settle only after a certain amount of time from the start of measurement, and that they are advancing rapidly. However, since the transmitted light intensity of this example is measured at a predetermined height from the cell bottom as described above, the transparency at that position is as shown in the figure. It is not transparent. Rather, the upper layer of the liquid to be treated starts to become transparent, and the transparent region changes so as to spread from the middle layer to the lower layer. Therefore, if the transmitted light intensity is measured at the upper layer, it is observed that the change in the transmitted light occurs in a shorter time.

  The liquid to be treated was the same as in Example 1, and the measurement position of transmitted light intensity (%) was 1 mm below the water surface. The applied voltage is a DC voltage of 0.3 V / mm, and the measurement results are shown in FIG.

  This test is intended to measure the time until the fine particles start to settle, and although it cannot be said unconditionally depending on the fine particles and other conditions, it can be seen that the test starts at least about 120 seconds (s) in this embodiment. . Moreover, since the transparency increases sharply when sedimentation begins, the aggregation of fine particles gradually increases, and the size grows irreversibly to the level of sedimentation, and it is difficult to think of growing while repeating aggregation and dispersion. It suggests.

  The liquid to be treated was the same as in Example 1, and the applied voltage was a direct current having an electric field strength of 0.3 V / mm. It was examined in detail how long the transmitted light intensity started to change (aggregate). The result is shown in FIG.

  From FIG. 4, it can be seen that aggregation starts within 1 second after the application of the electric field, whereby the transmitted light intensity once decreases. This is considered to be due to the fact that in the state where fine particles are uniformly dispersed, the scattering of light becomes stronger due to the start of aggregation. As the agglomeration further proceeds, the transmitted light intensity begins to rise as the particles settle.

  A DC voltage having an electric field strength of 0.3 V / mm was applied in the same manner as in Example 1 except that methanol was used as the solvent for the liquid to be treated. In addition, the electrode used the tin oxide instead of the platinum electrode. The reason for this is to clarify that when a platinum electrode is used, the silver paste connecting the conducting wire for voltage application is dissolved in methanol, and that the electrode other than platinum also exhibits an effect. An electrode is used. The change in transmitted light intensity (%) of the liquid to be treated in this case was measured, and the result is shown in FIG.

  As shown in FIG. 5, it can be seen that the intensity of transmitted light is faster when the electric field is applied than when no electric field is applied. Since bentonite particles are difficult to maintain a floating state in a solvent such as alcohol, they gradually settle even in the absence of an electric field, but aggregation and sedimentation are further promoted by the method of the present invention.

  A liquid to be treated similar to that in Example 1 was used, and direct current voltages of 0.09 V / mm, 0.1 V / mm, 0.3 V / mm, and 1.0 V / mm were applied. The change in transmitted light intensity of the liquid to be treated at this time was measured, and the result is shown in FIG.

  FIG. 6 shows that under the conditions of this example, the agglomeration effect is not observed when the electric field strength is 0.09 V / mm, and the agglomeration effect is observed when the electric field strength is 0.1 V / mm or more, and at least 0.3 V / mm. It can be seen that a sufficient agglomeration effect is exhibited when the electric field strength is mm.

  A DC voltage having an electric field strength of 0.3 V / mm was applied in the same manner as in Example 1 except that hectorite having a particle diameter of 45 μm was used as the fine particles of the liquid to be treated. The result is shown in FIG.

  Since the hectorite of this example has a high water permeability at a volume fraction of 0.0005, the transmitted light intensity is about 94% from the beginning. And if it is an electric field, it will float in water with this state, but if the electric field strength of 0.3 V / mm is applied, it can be set to the transmitted light intensity of about 100.

  A DC voltage having an electric field strength of 0.3 V / mm was applied in the same manner as in Example 1 except that monodisperse polymethyl methacrylate (hereinafter abbreviated as PMMA) having an average particle diameter of 5 μm was used as the fine particles of the liquid to be treated. The result is shown in FIG.

  As shown in FIG. 8, even in the absence of an electric field, PMMA gradually settles. However, it can be seen that aggregation and sedimentation can be promoted by applying an electric field. Although this example is intended for organic fine particles instead of the inorganic fine particles exemplified above, the present invention can be applied regardless of organic or inorganic.

  A DC voltage having an electric field strength of 0.3 V / mm was applied in the same manner as in Example 7 except that polydisperse polymethyl methacrylate (hereinafter abbreviated as PMMA) having an average particle diameter of 5 μm was used as the fine particles of the liquid to be treated. The result is shown in FIG.

  FIG. 9 shows that unlike in Example 7, in the case of no electric field, aggregation / precipitation of fine particles hardly occurs. This result comes from the difference between the monodispersion and the polydispersion shown in the previous example, but PMMA with a particle size of about 5 μm originally tends to aggregate in water, and if the particle size is smaller than that, it disperses in water. This suggests that it exists stably. In other words, polydispersed PMMA has an average particle size of 5 μm from the smallest to a larger particle size of 5 μm, so naturally it includes PMMA smaller than 5 μm and larger PMMA and has a smaller particle size. More PMMA is contained. Since the PMMA having a particle size smaller than 5 μm floats stably in water, the transparency of the liquid to be treated does not easily increase even if a larger PMMA settles. However, it can be understood that even the PMMA having such a small particle diameter that hardly aggregates can be easily settled by applying the present invention. Aggregation proceeded faster than in the case of monodispersion. This is presumably because PMMA having a small particle size is aggregated into PMMA having a large particle size to accelerate the sedimentation rate.

  Electric field strength of 0.3 V / mm was the same as in Example 1 except that bentonite particles having a particle size of 2.3 μm and polydisperse polymethyl methacrylate (hereinafter abbreviated as PMMA) having an average particle size of 5 μm were used as fine particles of the liquid to be treated. The DC voltage was applied. The result is shown in FIG.

  FIG. 10 shows that the coagulation effect can be exhibited by the method of the present invention even in a situation where organic fine particles and inorganic fine particles are mixed. Moreover, when it presumes from the condition which becomes transparent rapidly, it is estimated that each organic fine particle (PMMA) and inorganic fine particle (bentonite) do not aggregate selectively, but each fine particle aggregates indiscriminately. The If it is selective aggregation, the aggregation rate of each (organic / inorganic fine particles) will be somewhat different, and in such a case, it will not become transparent at least abruptly, but will have a certain width. It is because it is thought that it will become transparent.

  A DC voltage having an electric field strength of 0.3 V / mm was applied in the same manner as in Example 1 except that titanium oxide having a particle size of 25 μm was used as the fine particles of the liquid to be treated at a volume fraction of 0.00024. The result is shown in FIG.

  As shown in FIG. 11, the titanium oxide of this example does not have a very high dispersion stability in water. However, it can be seen that application of the present invention accelerates the sedimentation velocity. Since titanium oxide has various functions such as strength, lightness, heat resistance, corrosion resistance, and catalytic activity, it is used in a very wide range of fields. Therefore, it is shown that the method of the present invention is highly useful for the purpose of purifying industrial wastewater and domestic wastewater.

  As shown in the above examples, the intermolecular attractive force inherent to each other in the fine particles by disturbing the electric double layer on the fine particle surface existing in the liquid to be treated by the fine particle aggregation method of the present invention and lowering the zeta potential. Will act. In general, fine particles having different sizes are present in the liquid to be treated, and therefore, more effective separation and removal can be achieved by agglomeration of small and large fine particles.

  The fine particle agglomeration method of the present invention can be carried out with a simple configuration in which a plurality of electrodes are inserted into a liquid to be treated, so that environmental purification for industrial wastewater and domestic wastewater, and dispersion in water in production processes of ink, cosmetics, pharmaceuticals, etc. Many applications are expected, such as homogenizing, separating, and purifying fine particles.

DESCRIPTION OF SYMBOLS 1 Quartz cell 2 Platinum electrode 3 Transmitted light 4 Power supply voltage 5 Fine particle

Claims (2)

Insert multiple electrodes into the liquid to be treated in which fine particles are dispersed,
A method for agglomerating fine particles, characterized in that a voltage is applied between electrodes so that an electric field strength of 0.1 to 100 V / m is obtained.   The fine particle aggregation method according to claim 1, wherein the voltage application time is between 0.1 and 1000 seconds.

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