JP2006021079A - Contaminant removal method using electro-osmosis stream and contaminant removal apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve removal efficiency or recovery efficiency of a contaminant. <P>SOLUTION: AC voltage is superposedly applied, in addition to DC voltage, to treating objects, e.g., polluted soil, sludge or incineration ash containing harmful contaminants 5, such as heavy metals like lead, mercury, cadmium, arsenic, chromium, zinc, manganese or beryllium, harmful organic compounds like PCB (polychlorobiphenyls) or dioxins, or organic metal compounds, to cause vibration on solid phase particles 1 in the treating objects. Thus, while preventing the solid phase particles 1 from changing into a dense condition, moisture in the treating objects is moved by electro-osmosis stream Y, to efficiently remove and recover the contaminants 5. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a contaminant recovery technique using an electroosmotic flow. More specifically, the present invention relates to a technique for improving the recovery efficiency of pollutants by applying an alternating voltage to a direct current voltage in the electroosmotic flow formation stage.

  In recent years, there has been a problem of soil contamination due to harmful pollutants such as chromium, lead, mercury and other heavy metals, PCB, dioxins and other organic compounds, and organometallic compounds when redeveloping the factory site. In addition, there is a strong demand for the development of an effective recovery treatment technique for the harmful pollutants contained in sludge, sludge, incineration ash, and the like.

  Taking soil purification technology as an example, technologies such as soil oxidation, bioremediation, phytoremediation, and electroremediation have been proposed. However, these technologies are associated with the occurrence of secondary contamination, high costs, and long treatment times. And there are problems such as differences in purification capacity depending on the type of soil.

  As a soil purification technique, a method using an electroosmosis phenomenon has been proposed. That is, it is a technique for recovering contaminants contained in soil by applying a DC voltage to the soil and moving soil water in one direction by electroosmotic flow. Advantages of this technology are that harmful substances can be recovered in a solution state, low cost, in-situ purification can be performed, and treated soil can be reused.

  For example, in Patent Document 1, contaminated soil or sludge is interposed between an anode and a cathode, a liquid is present in the anode, a DC voltage is applied, and harmful substances are moved together with the liquid by electroosmosis or the like. A technique for recovering and then electrolyzing the recovered liquid is disclosed.

  In Patent Document 2, an electroosmosis phenomenon is generated by a DC voltage, and contaminated soil water and cleaning water in the contaminated soil are moved from the anode side to the cathode side to cover the electrode member on the cathode side. A technique is disclosed in which contaminants are adsorbed and contaminated water is collected and pumped into a hollow tube.

  In Patent Document 3, in a dehydration apparatus using an electroosmosis phenomenon obtained by applying a DC voltage, a technique for removing and cleaning a solvent containing contaminants transferred from a positive electrode to a negative electrode from a material to be treated (soil). Is disclosed.

  Patent Document 4 discloses a technique for imparting an electroosmotic effect to a contaminated soil widely and uniformly by applying a DC voltage to planar positive and negative electrodes arranged above and below a container for storing the contaminated soil.

In Patent Document 5, using a center electrode and a plurality of peripheral electrodes surrounding the center electrode, a DC voltage is applied in parallel between the electrodes to dehydrate the soil by electroosmosis, and then the polarity of the applied voltage is reversed. Thus, a technique for preventing secondary contamination by restoring the pH value of the treatment area is disclosed.
Japanese Patent Application Laid-Open No. 08-281247. Japanese Patent Application Laid-Open No. 08-155429. Japanese Patent Laid-Open No. 06-287933. JP 2002-035736 A. Japanese Patent Laid-Open No. 06-226300.

  Conventional soil remediation techniques using electroosmosis have not been widely used because of the problem of differences in the removal efficiency of pollutants due to differences in soil properties. This problem is thought to be due to various parameters of the soil.

  For example, the adsorption of pollutants to soil makes it difficult to move pollutants by electroosmosis flow (EOF). In addition, when an osmotic flow is caused by applying a DC voltage, the movement of the solution (water in the soil) is caused by the influence of electrophoresis and the fine particles that move in one direction due to the electroosmotic flow enter the gap between larger particles. This hinders the technical problem that the removal or recovery efficiency of pollutants is significantly reduced.

  Accordingly, the main object of the present invention is to provide a pollutant recovery method and pollutant recovery apparatus using electroosmotic flow that can significantly improve the removal or recovery efficiency of pollutants contained in soil and the like. To do.

  First, after many years of diligent research, the present inventors applied an AC voltage superimposed on a DC voltage used to form an electroosmotic flow, and this AC voltage caused vibration (vibration) to particles. By providing this, it is possible to effectively prevent the phenomenon that the particles of the object to be treated such as soil particles become dense during the movement process due to the electroosmotic flow. It has been newly found that the removal or recovery efficiency can be significantly improved.

  Therefore, in the present invention, firstly, a DC voltage is applied to an object to be treated containing a contaminant, and moisture in the object to be treated is moved by an electroosmotic flow to thereby remove the contaminant from the object to be treated. And a contaminant removal method for superimposing an AC voltage on the DC voltage in the step of forming the electroosmotic flow. That is, this method is characterized in that the contaminant-containing water in the object to be processed is moved to the electrode side by employing an electroosmotic flow while applying vibration to the object particles (for example, soil particles).

  Here, although the said to-be-processed object is not specifically limited, For example, in the case where it is one selected from soil, sludge, sludge, incineration ash (including fly ash), or this combination, this invention is Particularly preferred. In the present invention, the AC voltage superimposed on the DC voltage is preferably a low-frequency AC voltage.

  Further, the application of the AC voltage may be a method in which the DC voltage is applied in parallel over the entire time during which the DC voltage is applied, but is not limited thereto, and it is possible to reliably achieve uniform electroosmotic flow. The number of times or the application timing may be appropriately selected according to conditions such as the type of the object to be processed.

  For example, (1) from the start of DC voltage application until the end of voltage application until the end of voltage application, (2) intermittently after application of DC voltage, and (3) from application start to end of DC voltage application When an AC voltage is applied at a timing such as within a predetermined time, electric energy can be saved. As the scope of implementation of the method becomes wider or the scale of the apparatus for carrying out the method increases, the saving effect of electric energy increases.

  Next, in the present invention, secondly, the moisture in the workpiece is moved by electroosmotic flow by means capable of applying an alternating voltage and a direct current voltage to the workpiece containing the pollutant, Provided is a pollutant removing device that removes the pollutant from the object to be treated.

  This device can reliably collect harmful pollutants in a solution at a low cost, and can be purified in situ. Further, since harmful pollutants can be reliably removed from the treated object such as the soil subjected to the purification treatment, the treated object can be reused.

  According to the present invention, particles of an object to be treated, such as soil particles, are applied by superimposing an AC voltage on a DC voltage used to form an electroosmotic flow, and vibrating the particles (vibration action) by the AC voltage. Can be effectively prevented from becoming dense. As a result, the electroosmotic flow can be generated uniformly, and the contaminant removal or recovery efficiency can be significantly improved.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments for carrying out the invention will be described with reference to the accompanying drawings. Each embodiment shown in the attached drawings shows an example of a typical embodiment of the thing and method concerning the present invention, and, thereby, the scope of the present invention is not interpreted narrowly.

  First, FIG. 1 is a conceptual diagram of the basic configuration of an apparatus for carrying out the pollutant removal method according to the present invention (when the zeta potential of particles is a positive value), and FIG. 2 is another basic configuration of the apparatus. Is a conceptual diagram (when the zeta potential of the particle is a negative value).

  When a voltage is applied to a system in which the solid phase particle 1 and the liquid phase 2 exist, charge separation occurs at the interface between the solid phase particle 1 and the liquid phase 2, and a layer called an electric double layer 3 is formed. At this time, when the zeta potential of the solid phase particle 1 shows a positive value (see FIG. 1), when a DC voltage is applied to the liquid phase 2, the solvent 4 in the vicinity of the solid phase particle 1 has a weak reverse charge. (In this case, it has a negative charge). On the other hand, when the zeta potential of the solid phase particle 1 shows a negative value (see FIG. 2), when a DC voltage is applied to the liquid phase 2, the solvent 4 in the vicinity of the solid phase particle 1 has a weak reverse charge. (In this case, it has a positive charge).

  Reference numeral 5 shown in FIGS. 1 and 2 indicates harmful pollutants made of heavy metals and harmful organic compounds present in the liquid phase 2. Heavy metals are, for example, lead, mercury, cadmium, arsenic, chromium, zinc, manganese, beryllium and the like, and harmful organic compounds are PCB (polychlorinated biphenyls), polychlorinated dibenzoparadoxins (PCDDs), polychlorinated dibenzofurans (PCDF). ) And other organic chlorinated solvents such as trichlorethylene and tetrachloroethylene.

  When a DC voltage is applied to the liquid phase 2 in which the harmful pollutant 5 exists, an electroosmotic flow Y is formed in the vicinity of the electric double layer 3 (in the direction opposite to the electrophoresis direction (X)). By causing the liquid phase 2 (for example, water in the soil) to flow toward the anode or the cathode side by the electrodynamic action of the electroosmotic flow Y, the harmful pollutant 5 contained in the liquid phase 2 is obtained. It can be moved to the anode or cathode side and recovered.

  However, as shown in FIGS. 1 and 2, the direction of the electroosmotic flow Y and the direction of the electrophoretic X of the fine solid phase particle 1a are opposite, which affects the electrodynamic action of the electroosmotic flow Y. Will affect. Furthermore, when a DC voltage is applied, the solid phase particles gradually become dense, and the flow of the liquid phase 2 is inhibited. For these reasons, the removal effect (recovery effect) of the pollutant 5 by the electroosmotic flow Y is reduced.

  The change in which the solid phase particles 1 gradually become dense will be described using, for example, the models shown in FIGS. 1 and 2. For example, there are many finer solid phase particles 1a between the solid phase particles 1 and 1. It can be considered that the liquid phase 2 is gradually narrowed by entering. When the solid phase particle 1 is positively charged, the solid phase particle 1a becomes dense and clogged on the cathode side, and when the solid phase particle 1 is negatively charged, the solid phase particle 1a is on the anode side. Becomes dense and clogged.

  Therefore, if the AC voltage is applied so as to be superimposed on the DC voltage, the AC voltage vibrates the fine solid-phase particles 1a and effectively changes the solid-phase particles 1a in a dense state. Can be prevented. That is, the electroosmotic flow Y can be uniformly formed in the liquid phase 2.

  Next, FIG. 3 is a diagram schematically showing a preferred embodiment of the contaminant removal apparatus according to the present invention.

Reference numeral 10 in FIG. 3 indicates a contaminant removal apparatus (hereinafter abbreviated as “apparatus”). The apparatus 10 includes a storage unit 11 for storing the workpiece 6, a cleaning water supply unit 12 for supplying the cleaning water W ₁ to the storage unit 11, and contaminated water moved by the electroosmotic flow Y. A contaminated water recovery unit 13 for primary storage of W ₂ .

At both ends of the accommodating portion 11, the mesh-like counter electrodes E ₁ -E ₂ capable of passing a solution is provided. The counter electrodes E ₁ -E ₂ are connected to a DC power supply G, and can adopt a configuration in which a DC voltage can be applied to the washing water W ₁ flowing into the storage portion 11 by an on / off operation of the switch S _1. Has been. In addition, the code | symbol A in FIG. 1 represents the ammeter.

The DC power supply G, AC oscillator 14 is connected via a switch S _2, i.e., the on / off operation switch S _2, a configuration capable of freely superimposed application at a predetermined timing an AC voltage on a DC voltage ing. Even if it is not this structure, if it is a circuit which can superimpose an alternating voltage on a direct voltage, it is employable.

  Here, the frequency of the alternating voltage and the optimum conditions for the amplitude can be determined by factors such as the size distribution of the solid phase particles and the zeta potential. For example, the optimum condition may be found and set according to the type and properties of the workpiece 6.

  Here, FIG. 4 is a timing chart showing a typical example of the voltage application procedure.

  The present invention is characterized in that the alternating voltage (AC) is superimposed and applied to the direct voltage (DC). As a suitable procedure example of the voltage application, first, as shown in FIG. As described above, it is possible to adopt a procedure in which an alternating voltage is continuously applied to a direct current voltage over the entire process of the voltage application process.

  Next, as shown in FIG. 4 (II), a procedure of applying an AC voltage superimposed on a DC voltage from the latter half of the voltage application process can be employed. The AC voltage application start timing is preferably before the change in which the solid phase particle 1 (1a) becomes dense appears.

  Further, as shown in FIG. 4 (III), a procedure for intermittently applying an AC voltage to a DC voltage, or as shown in FIG. 4 (IV), applying a DC voltage. The AC voltage may be superimposed and applied only within a predetermined time during the process.

  Which voltage application procedure is adopted may be appropriately selected depending on, for example, the type and properties of the object 6 to be processed. However, when compared with the voltage application procedure (I), the voltage from (II) to (IV) The application procedure is advantageous in that power consumption can be saved.

  The inventors of the present invention have a main purpose of verifying the effects of the present invention, a test in which only a DC voltage is applied (comparative example), and a test in which a low-frequency AC voltage is superimposed on a DC voltage (Examples 1 to 1). 4) was carried out. That is, the effects of the present invention were verified by comparing and comparing the results of Examples 1 to 4 with the results of Comparative Examples.

  In addition, among Examples 1 to 3 in which alumina particles having a positive zeta potential are assumed as soil particles, “Example 1” (alumina particles: average particle size 3.3 μm (particle size 1 to 6 μm), “implementation” In “Example 2” (alumina particles: average particle size 3.8 μm (particle size 1 to 9 μm)), suitable conditions for the frequency of the AC voltage were verified, and “Example 3” shows the amplitude of the AC voltage (Amplitude, amplitude). “Example 4” is a test in which kaolin particles having a zeta potential opposite to those in Examples 1 to 3 are assumed as soil particles.

  A series of tests were performed using a simulated voltage application device 20 having a configuration as shown in FIG. The apparatus 20 includes a glass cylindrical cell 21 having an inner diameter of 1.0 cm and a length of 5.0 cm. The cylindrical cell 21 contains alumina nitrate (aluminum oxide, Kishida Chemical special grade reagent, average particle size) containing copper nitrate solution (0.1 mol / L) adjusted to pH 5 with acetic acid / sodium acetate (buffer solution). 3.3 μm (particle size 1 to 6 μm) (“Example 2” is filled with an average particle size of 3.8 μm (particle size 1 to 9 μm), and four electrodes (reference electrodes 22a and 22b: An experiment of removing copper as a pollutant was performed using Ag / AgCl, counter electrodes 23a and 23b: mesh platinum, and a membrane filter (Millipore, pore size: 0.1 μm) and covered both ends of the cylindrical cell.Acetic acid / sodium acetate solution of pH 5 was used as the electrolytic solution, and alumina particles were assumed to be soil particles having a positive zeta potential. It is.

  A non-illustrated potentiostat (4-electrode potentiostat HV-501 manufactured by Hokuto Denko Co., Ltd.) was connected to each electrode in the electrolyte solution outside the cylindrical cell 21 so that a constant potential could be applied by the four-electrode method. . In this "four-electrode method", the voltage applied between the counter electrodes 23a-23b is controlled by reference electrodes 22a-22b placed at both ends of the sample, and an accurate constant potential is applied to the sample. Adopted to make it possible and used instead of DC power supply. That is, in this experiment, an accurate voltage and current value are obtained by applying a voltage with a potentiostat through four electrodes.

By connecting an AC oscillator (not shown) (manufactured by Stanford Research Systems, using only the built-in oscillator of the lock-in amplifier SR830) to the potentiostat, an AC voltage can be superimposed and applied to the DC voltage. In addition, the application condition of alternating voltage was confirmed with the oscilloscope.
(Comparative example)
The DC voltage was set to 5 V (1.0 V / cm), and electrolysis was performed for 6 hours under the voltage conditions (without applying an AC voltage superimposed). The solution in the cylindrical cell 21 was adjusted to pH 5 by using an acetic acid / sodium acetate buffer solution. Copper was quantified by using a plasma emission spectroscopic analyzer (JCAP-757 ICAP-757). In the following results, with respect to the amount of copper added to the particles in the cylindrical cell, the amount of copper transferred to the anode or cathode side container was expressed as recovery rate (%) = (copper transfer rate / copper addition). Amount) x100.

  The results are shown in the following “Table 1”. In this test as well, the particles assumed as a model of soil particles are alumina particles having the same particle size as those of Example 1 and Example 3 described later.

  As shown in the above-mentioned “Table 1”, in the electroosmosis phenomenon when no AC voltage is applied (in the case of only DC voltage), the recovery of copper ions assumed as a contaminant is very low. That is, the proportion of copper recovered in the anode side solution was only 1.0% (see “Table 1”).

  Since the zeta potential of alumina particles is a positive value, copper ions (divalent cations) should move to the anode side according to the principle of electroosmosis (see FIG. 1). The result was the opposite.

  This is because the direction of electroosmotic flow Y in alumina is opposite to the direction of migration of copper ions (the same direction as the electrophoresis of fine solid phase particles), thus reducing the copper ion removal effect (recovery effect). Can be estimated.

  Further, it was confirmed that the alumina particles on the cathode side after the end of this comparative example test were in a dense state and were tightly packed in the cell. From this result, it was estimated that the fact that the particles became dense by electrophoresis and the movement of the solution did not occur due to clogging was also a major factor that reduced the copper recovery effect by electroosmotic flow. .

Example 1
Next, a test was conducted to investigate the copper recovery effect when a low-frequency AC voltage was superimposed on the DC voltage, and the relationship between the AC voltage frequency and the copper recovery rate assumed for the contaminant.

  More specifically, the frequency condition of the AC voltage is set to 0 Hz (that is, only the DC voltage: the control section), 2 Hz, 5 Hz, and 10 Hz, and the amplitude is set to 0.283 V (0.056 V / cm). The test was conducted with setting. The DC voltage was set to 5 V (1.0 V / cm), and electrolysis was performed for 6 hours under the superimposed application condition of AC voltage.

  The results of this test are shown in “Table 2” below. This "Table 2" shows the copper ion concentration of each of the anode side solution and the cathode side solution for each frequency condition.

  As shown in the above-mentioned “Table 2”, in the recovery of copper in the presence of alumina particles having a positive zeta potential, the optimum frequency condition was 5 Hz. The efficiency with which copper can be recovered by electroosmotic flow was about 17 times (17.4 / 1.0) higher than when no AC voltage was applied (see Comparative Example, “Table 1”).

(Example 2)
Next, an experiment similar to that of Example 1 was performed using alumina particles having a larger particle diameter than that of Example 1. The frequency of the alternating voltage was 0.5 Hz, 5 Hz, 20 Hz, and 30 Hz. In this test, a “control group” to which only a DC voltage was applied was prepared, and the result was compared with the result in the case of applying an AC voltage. The results of this test are shown in the following “Table 3”.

  As shown in the above-mentioned “Table 3”, even in the case of a system in which the average particle diameter of alumina particles is large, the concentration of copper ions in the anode-side solution is increased by applying an alternating voltage to the direct current voltage. Thus, it was found that the removal or recovery efficiency of copper ions can be improved.

  Similar to the result of “Example 1” described above, the copper ion concentration in the anode side solution was highest when the frequency was 5 Hz. Further, an increase in the copper recovery rate in the anode side solution was observed even at a frequency of about 0.5 Hz, and an increase in the copper recovery rate in the anode side solution was also observed in the frequency range of 20 Hz and 30 Hz. It was.

  Further, when the results of “Example 2” and the results of “Example 1” were compared, Example 2 which is a system in which the average particle diameter of the alumina particles is large showed better copper ion removal or recovery efficiency. For example, the copper recovery rate of the anode side solution at a frequency of 5 Hz was 17.4% in Example 1, whereas it was 23.6% in Example 2. This is thought to be because the system in which the average particle diameter of the alumina particles is larger is less likely to cause the alumina particles to change to a dense state.

  As a result of the above “Example 1” and “Example 2”, alumina particles that can be assumed as soil particles are forcibly vibrated by a low-frequency alternating voltage applied in a superimposed manner, thereby bringing the alumina particles into a dense state due to electric field formation. It can be presumed that this change was prevented and the solution in the sample could be moved efficiently.

Example 3
Next, in order to examine the optimum condition of the amplitude, the test was performed by setting the frequency of the AC voltage to 5 Hz. The amplitude conditions were 0.071V, 0.141V, 0.283V, and 0.566V. The alumina particles used are the same as those in Example 1. The results are shown in the following “Table 4”. This "Table 4" shows the copper recovery rate of each of the anode side solution and the cathode side solution for each frequency condition.

  As shown in the above-mentioned “Table 4”, the highest recovery rate was obtained under the condition of an amplitude of 0.141 V, and the copper recovery rate in the anode side solution was about 22%. This corresponds to about 6 times the 0.071V condition.

Example 4
Next, about kaolin often used as a soil model (high-grade soil, chemical reagent manufactured by Wako Pure Chemical Industries, average particle size 6.9 μm (particle size 1 to 12 μm) (zeta potential is minus opposite to alumina), An experiment similar to Examples 1 to 3 was performed under the condition of a moisture content of 31%, which corresponds to the model shown in FIG.

  As a result, in the condition without AC voltage application (control group), the copper recovery rate was 13.5% for the cathode side solution (0.96% for the anode side solution), whereas the frequency was 5 Hz. When an alternating voltage with a condition of 0.141 V was superimposed on the direct voltage, a copper recovery rate of 29.7% on the cathode side (0.58% on the anode side) was obtained. The results are summarized in the following “Table 5”.

  From the result of “Example 4”, it was verified that the removal efficiency (recovery efficiency) of copper can be improved by the AC voltage even under the condition where particles having a negative zeta potential exist.

  From the results of the above tests, it was found that the copper recovery rate was greatly improved by applying an alternating voltage to the direct voltage. It was also verified that the removal efficiency (recovery efficiency) can be further improved by obtaining the optimum conditions from the viewpoint of frequency and amplitude.

  Therefore, the present invention can be evaluated as a completely new method as a contaminant removal method for contaminated soil and the like, and can be applied not only to contaminated soil but also to separation of solutes in a system containing small particles. it is conceivable that.

  Furthermore, it has been clarified that the recovery efficiency of copper ions can be improved in both systems where alumina particles (plus) and kaolin particles (minus) with different zeta potentials exist. The present invention is considered to be useful as a purification technique for processed products.

  A method or apparatus according to the present invention includes a heavy metal such as lead, mercury, cadmium, arsenic, chromium, zinc, manganese, and beryllium, a harmful organic compound such as PCB and dioxins, and a soil containing a harmful pollutant such as an organometallic compound, It can be used as a technology for removing and collecting contaminants such as sludge, sludge, and incinerated ash.

It is a conceptual diagram (when the zeta potential of particles is a positive value) of a basic model of an apparatus for carrying out the pollutant removal method according to the present invention. It is a conceptual diagram (when the zeta potential of particles is a negative value) of another basic model of the device. It is a figure showing simply a suitable embodiment of the device. It is a timing diagram which shows the typical example of the procedure of a voltage application. It is a figure which shows schematic structure of the electrolyzer employ | adopted by the test concerning an Example and a comparative example.

Explanation of symbols

1 Solid phase particles (1a Fine solid phase particles)
2 Liquid phase 3 Electric double layer 5 Hazardous pollutant Y Electroosmotic flow

Claims (5)

  A method for removing contaminants from the object to be treated by applying a DC voltage to the object to be treated containing a contaminant and moving moisture in the object to be treated by electroosmotic flow. A pollutant removal method, wherein an alternating voltage is superimposed on the direct current voltage in the step of forming an osmotic flow.   The pollutant removal method according to claim 1, wherein the object to be treated is one selected from soil, sludge, sludge, and incinerated ash, or a combination thereof.   2. The pollutant removal method according to claim 1, wherein the AC voltage is a low-frequency AC voltage. 2. The contaminant removal method according to claim 1, wherein the application of the AC voltage is performed at any one of the following timings (1) to (3).
(1) From the start of application of a DC voltage until the end of voltage application from the lapse of a predetermined time.
(2) After applying DC voltage, intermittently.
(3) Within a predetermined time from the start to the end of application of DC voltage.   The contaminants are removed from the object to be treated by moving the moisture in the object to be treated by means of an electroosmotic flow by means capable of applying an alternating voltage and a direct current voltage to the object to be treated containing the contaminants. A pollutant removing device characterized by that.

Images