JP3363979B2 - Water treatment equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water treatment apparatus for treating a liquid to be treated containing a metal component and an organic component to recover the metal component and decompose the organic component. The present invention relates to an electrolytic treatment device for wastewater, which electrolytically treats wastewater containing valuable metals such as the above and organic additives.

[0002]

2. Description of the Related Art Due to strict regulations on wastewater in Japan, factory wastewater, etc. are all treated and discharged after conforming to the wastewater regulations. The wastewater treatment method is mainly a neutralization precipitation method, and this method causes the metal to precipitate as a hydrate or hydroxide by shifting the pH of the wastewater from a neutral range to a weak alkalinity, and this is filtered off, If necessary, the filtrate is treated with resin and further advanced treatment to remove p
This is a method of releasing H after conforming to regulations.

This neutralization precipitation method is theoretically very effective, but as described above, it is not always effective in removing organic COD such as organic additives, and it is not possible to use ozone or hydrogen peroxide. Oxidation treatment is often required, and the existence of this additional step is a major obstacle to achieving efficient wastewater treatment. Although the neutralization precipitation method is effective for recovering free metal ions, it is not suitable for recovering metal ions in the form of metal complex ions present in organic complexes such as chelates, and thus resin treatment, chelate There is also a problem that an additional step such as disassembly is required.

Further, it is often difficult to easily and inexpensively isolate and recover the metal from the metal hydroxide precipitated by the neutralization precipitation method, and the metal recovery by the neutralization precipitation method is economical. Actually, it is hardly done because of the problem. It is known that the electrolytic recovery of the metal from the waste water is also effective because the target metal is recovered not as a compound but as an isolated metal and the isolation step is unnecessary. Furthermore, since the electrolysis method can be carried out relatively inexpensively,
Several types of waste liquid treatment devices intended for electrolytic metal recovery are commercially available and put into practical use.

These electrolytic metal recovery devices are devised so that the surface area of the cathode with which the metal ions come into contact is as large as possible in order to effectively reduce the metal ions. The mainstream is that the anode or a metal anode having a three-dimensional spread is installed, or the cathode side is filled with carbon particles to form a fixed bed type, and the liquid to be treated is caused to flow to the cathode side for electrolysis. Has become. In this type of electrolytic cell, the liquid to be treated is passed between the two electrodes in order to smoothly conduct electricity, or both electrodes are separated by an ion exchange membrane and electrolytic solution such as dilute sulfuric acid is applied to the anode chamber side and the cathode chamber side is exposed. I am flowing the processing liquid. The cathode of these electrolytic cells is basically a monopolar structure and can have an extremely large surface area, which is advantageous for metal recovery, but no consideration is given to the treatment of organic COD or the like contained in the liquid.

As another electrolysis method, a method of using an electrolysis cell in which conductive carbon particles are filled between an anode and a cathode is known. In this method, the carbon particles themselves have a potential difference due to electric resistance within the particles, and the energization causes negative polarization on the anode side and positive polarization on the cathode side, whereby a plurality of carbon particles existing between the anode and the cathode have a bipolar structure. By functioning as, the voltage is increased, but it is intended to effectively recover the metal with a small current. However, even in this method, since carbon particles cannot be expected to exert any effect on the decomposition of organic COD, it is clear that the decomposition of organic COD is not considered at all and only metal recovery is paid attention. Furthermore, a method of recovering precious metals by fluidized bed type electrolysis using carbon particles as a cathode for recovering precious metals from precious metal waste liquid has been proposed, but even in this method, only precious metal recovery is noted, and it is included in many waste liquids. Little attention is paid to the removal of the organic COD, and it is considered that the removal of the organic COD should be performed in a separate step.

[0007]

OBJECTS OF THE INVENTION The present invention contains various organic wastes which normally require recovery of metals, in addition to metals, containing organic components which must be decomposed, and the metal recovery and the decomposition of the organic components are performed in a single manner. It is an object of the present invention to provide a water treatment device capable of performing metal electrodeposition and decomposition of organic components in a single operation, focusing on the fact that wastewater treatment can be performed efficiently if it can be performed by operation.

[0008]

The present invention comprises an electrolyzer filled with semiconductive fine particles containing titanium oxide between an anode and a cathode and a light source, wherein the filled fine particles contain a metal component and an organic component. A water characterized by supplying a liquid to be treated and applying a direct current between both electrodes of the electrolytic cell while applying light, recovering the metal components in the liquid to be treated and decomposing the organic components. It is a processing device.

The present invention will be described in detail below. The present inventors have conducted various studies on electrode materials capable of simultaneously performing electrodeposition by reduction of metal ions and decomposition of organic components, and have found that titanium oxide is the best electrode material, resulting in the present invention. . It is known that semiconducting titanium oxide decomposes water as a photocatalyst when exposed to light. The inventors of the present invention have paid attention to this property and have found that the semiconducting titanium oxide is used as an electrode substance to apply an electric current to decompose an organic component in an electrolytic solution.

Further, when the titanium oxide was installed in an electrolytic cell as a cathode for electrolysis and used for reducing metal ions in an electrolytic solution, it was also found that the reduced metal was electrodeposited on the surface and recovered. It was In the present invention, titanium oxide is used as fine particles to fill the space between the anode and the cathode of the electrolytic cell and used in the state where the electrolytic surface area is maximized, similarly to the conventional metal recovery using carbon particles.

When a current is applied between both electrodes, the titanium oxide is polarized and has a certain orientation, that is, the part facing the anode is negatively polarized and the part facing the cathode is positively polarized. In this way, the liquid to be treated containing metal ions and organic components is supplied to the electrolytic cell filled with titanium oxide, and both electrodes are irradiated with light from the light source so as to be preferably parallel to the longitudinal direction of both electrodes. When a direct current is applied between the titanium oxide particles, the metal ions are reduced in the negatively polarized portion of each titanium oxide particle to be deposited as a simple metal, and the reductive decomposition of the organic component is also positively caused in the negatively polarized portion by using the applied light as a catalyst. Oxidative decomposition of the organic component is carried out in the polarization part, so that metal recovery and organic component decomposition can be carried out simultaneously.

[0012] Of the two functions, there is almost no effect of light on the electrodeposition of metals. This is because the hydrogen overvoltage on the negative polarization side that determines metal electrodeposition is base for most metals and the light applied Is considered to have no effect on this overvoltage. Titanium oxide having both of the above functions is required to be semiconducting and have a large surface area, and such titanium oxide fine particles can be prepared as follows. That is, 100 to 300 mesh powder of natural rutile is placed in vacuum or in an inert / non-oxidizing atmosphere of nitrogen at 1100 ° C to 15 ° C.
Oxygen defects are formed in titanium oxide by heating and sintering at 00 ° C., that is, TiO _2−x is given conductivity to be a semiconductive oxide. Alternatively, natural rutile is pulverized to about 350 mesh, or synthetic rutile powder of similar particle size is kneaded as it is or with a small amount of titanium sponge and heated and baked at 1100 ° C to 1500 ° C in a reducing or inert atmosphere for 1 to 100 hours. To conclude. When titanium sponge is used as a reducing agent, it may be used in an oxidizing atmosphere.

The method of giving semiconductivity to titanium oxide is not limited to these, but may be sintered together with metals having different valences such as tantalum and niobium. To prepare semiconducting titanium oxide by this method, titanium oxide, tantalum oxide and niobium oxide are mixed in the form of fine powder to form a pellet, and if necessary, a titanium sponge is added, followed by firing under the above-mentioned conditions. It suffices if they are bonded, and a rutile type semiconductive oxide can be obtained even in an oxidizing atmosphere. The semiconducting titanium oxide prepared in this way was thoroughly crushed and weakly sintered at 1000 ° C or less with a small amount of foaming agent or binder to obtain a grain size
Use porous powder of about 10 to 200 mesh. As a result, semiconductive titanium oxide fine particles having a surface area about 10 times larger can be obtained.

The titanium oxide fine particles are filled in the space between the anode and the cathode installed in the electrolytic cell with a space. Since the fine particles are weakly bound to each other by the binder, they can be installed integrally between the electrodes in an arbitrary shape.
The electrolytic cell to be used is not particularly limited, but is preferably made of, for example, quartz glass, which is thin and has good transparency, in order to transmit the applied light and illuminate the entire titanium oxide fine particles.

The electrode to be used is not particularly limited, but it is desirable that the anode is a titanium substrate coated with semiconducting titanium oxide because both electrodes are not simply electrolyzed by water but decomposition of organic components occurs. In addition, since the decomposition of organic components hardly occurs at the cathode, a normal titanium electrode may be used. However, considering that higher voltage is applied than normal electrolysis and that halogen ions may exist in the liquid to be treated, titanium-tantalum alloy or titanium-niobium alloy is used as the electrode material instead of titanium with low breakdown voltage. It is desirable to use it as a base material. However, since these are expensive, they may be appropriately selected according to the application.

Needless to say, a titanium base material obtained by impregnating niobium or tantalum by sintering to form an alloy or a base material having a surface formed of niobium or tantalum can be used. The light to be applied to the electrolytic cell having such a configuration may be visible light, but it is desirable to use ultraviolet light having higher energy than visible light, and to effectively decompose organic components by ultraviolet light in almost all wavelength regions. You can Further, a direct current is used as a current to be passed between both electrodes, because when an alternating current is used, the metal simple substance once electrodeposited on the negative polarization part is redissolved by positive polarization.

The target liquid to be treated is not particularly limited as long as it contains metal ions and organic components, but it is difficult to reduce the amount of organic components to a level at which it can be discharged by ordinary treatment such as plating waste liquid. The present invention is particularly effective when used as a target. The liquid to be treated may be filled in the entire electrolytic cell for batch treatment, or may be flowed through the electrolytic cell in a flow state. The metal electrodeposited on the titanium oxide fine particles is oxidatively dissolved by electrolysis using the titanium oxide fine particles as an anode to be recovered as a solution containing the metal ions, or dissolved in an acid to be recovered as a metal solution. As a result, the titanium oxide fine particles return to the state before the electrolytic treatment and can be repeatedly used for the electrolytic treatment by the apparatus of the present invention.

FIG. 1 is a cross-sectional plan view showing an example of the water treatment device according to the present invention. 1 is an electrolytic bath for water treatment, which is made of a light transmissive material such as quartz glass, especially an ultraviolet ray transmissive material,
A plate-shaped anode 2 and a plate-shaped cathode 3 are installed near the left and right side walls in the electrolytic cell 1. A space between the electrodes 2 and 3 accommodates a filler layer 4 which is formed by mixing titanium oxide fine particles alone or particles of titanium oxide, tantalum oxide and niobium oxide and sintering them. Before and after the electrolytic cell 1 (up and down in the drawing), 1
A pair of ultraviolet lamps 5 are installed so that the filling layer 4 can be irradiated with ultraviolet rays through the front and rear wall surfaces of the electrolytic cell 1.

While supplying a liquid to be treated containing a metal component such as copper ions and an organic component such as a plating liquid additive from a liquid to be treated inlet (not shown) installed at the bottom of the electrolytic bath 1, When electricity is applied between both electrodes 2 and 3, the liquid to be treated comes into contact with the negatively polarized portion of the filling layer 4 and the metal ions in the liquid to be treated are reduced to simple metals, and the surface of the titanium oxide fine particles or the like of the filling layer 4 is reduced. To deposit. On the other hand, the organic component in the liquid to be treated comes into contact with the positively polarized portion of the packed layer 4 and is oxidatively decomposed and converted into a harmless component which can be discharged as it is. The metal simple substance electrodeposited on the surface of the packed layer 4 is taken out of the electrolytic cell 1 together with the packed layer 4 and treated with an acid to elute, or a pure metal ion-containing solution is obtained by electrolyzing the packed layer 4 as an anode. After being recovered, the packed bed 4 can be reused for the water treatment.

[0020]

EXAMPLES Next, examples of treatment of the liquid to be treated using the water treatment apparatus according to the present invention will be described, but the examples do not limit the present invention.

[0021]

[Example 1] To a synthetic rutile powder having a particle size of 350 mesh or less, a titanium sponge in an amount 1/10 that of metal was added as a metal, sufficiently mixed in a wet manner, and further press-molded into a pellet form, which was Semiconducting particles were prepared by sintering in air at 1300 ° C. for 2 hours. The electric resistance of this sintered pellet was 10 ^-2 Ωcm. The pellets were pulverized again, and a nonionic surfactant and dextrin were added to the pellets for foaming and solidification, and so-called dull sintering was performed at 900 ° C. Further, it was pulverized with a ball mill to obtain a 40 to 100 mesh granular material.

This granular material was filled in a box type electrolytic cell made of quartz glass having a thickness of 10 mm between an anode and a cathode placed at a distance of 10 cm, and the depth was set to 10 mm and the width and height were set. To form a 10 cm rectangular solid packed bed. The anode was a titanium substrate whose surface was coated with a complex oxide of tantalum oxide and titanium oxide, and the cathode was a titanium plate. Side wall where both electrodes of the electrolytic cell do not exist (200 ~ from 2 directions of 100 × 100 mm side)
While irradiating with ultraviolet rays having a wavelength of 400 using an ultraviolet lamp, 100 pp of copper ions were introduced into the electrolytic cell from the bottom.
m, the diluted sulfuric acid containing 150 ppm as a COD was supplied so that the diluted sulfuric acid could pass through the packed bed at a speed of 50 cm / min, and a direct current was passed between both electrodes to carry out electrolysis. CO in the liquid to be treated taken out of the electrolytic cell
D was 10 ppm or less and copper ion was 0.1 ppm or less. When the ultraviolet lamp was turned off while maintaining this state, COD increased to 20 ppm.

[0023]

Comparative Example 1 A liquid to be treated was treated under the same conditions as in Example 1 except that carbon powder was used in place of the semiconductive titanium oxide of Example 1 as a filling layer. The liquid to be treated becomes black and turbid, and the COD after filtration is 125-
140 ppm and copper ion content is 1.5 ppm
Therefore, although copper ion recovery can be performed at almost the same level, C
It was found that there was a problem with OD processing.

[0024]

[Example 2] Instead of adding titanium sponge to titanium oxide, purified tantalite (main components are tantalum oxide and niobium oxide) corresponding to one tenth molar amount of titanium oxide.
Example 1 except that the powder was added and sintered at 1500 ° C. for 2 hours
Semiconductive fine particles were prepared in the same manner as in. The semiconductive sintered particles were filled as porous particles in the same manner as in Example 1 between the anode and the cathode in the same electrolytic cell as in Example 1 as 40 to 100 mesh particles, and further under the same conditions as in Example 1. When electrolysis was performed, the treated liquid after treatment had a COD of 10 ppm or less and a copper ion content of 1 ppm or less.

[0025]

INDUSTRIAL APPLICABILITY The present invention comprises a light source and a light source in which semiconductive fine particles containing titanium oxide are filled between an anode and a cathode, and a liquid to be treated having a metal component and an organic component in the filled fine particles. The water treatment apparatus is characterized in that a direct current is applied between both electrodes of the electrolytic cell while supplying and applying light to recover the metal component in the liquid to be treated and decompose the organic component. Carbon particles used for conventional electrolytic wastewater treatment are effective in recovering metal ions in the wastewater, but have little effect in removing organic components contained in most wastewater.

The fine particles mainly composed of titanium oxide which constitute the packed bed used in the electrolytic cell of the water treatment apparatus of the present invention are effective not only for recovering metal ions but also for oxidative decomposition of organic components. However, by irradiating the filling layer with light, the metal recovery efficiency is hardly changed, but the decomposition of the organic component is greatly accelerated. When the liquid to be treated containing the metal component and the organic component is treated by the water treatment apparatus according to the present invention, the metal recovery and the organic component decomposition can be simultaneously performed with high efficiency in a single process. When titanium oxide is used alone as the particles that form the filling layer, it is desirable to generate oxygen defects in the particle structure to generate conductivity.

The particles can be made conductive by mixing tantalum or niobium, which is an oxide of a metal having a different valence from the titanium oxide particles, and sintering the particles. The light used may be visible light, but it is desirable to use ultraviolet light having higher energy than visible light in order to enhance the decomposition efficiency of organic components, and in order to effectively utilize the visible light or ultraviolet light, the electrolytic It is desirable that the wall surface of the tank be made of a material that transmits visible light and ultraviolet rays.

[Brief description of drawings]

FIG. 1 is a cross-sectional plan view showing an example of a water treatment device according to the present invention.

[Explanation of symbols]

1 ... Electrolyzer for water treatment 2 ... Anode 3 ... Cathode 4 ... Packing layer 5 ... UV lamp

─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-52-11643 (JP, A) JP-A-48-89548 (JP, A) JP-A-5-155726 (JP, A) JP-A-60- 187322 (JP, A) JP 60-118289 (JP, A) JP 60-118236 (JP, A) JP 5-200387 (JP, A) JP 60-28884 (JP, A) JP-A-4-61933 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C02F 1/461 C02F 1/32 C02F 1/72 C25C 7/00

Claims (4)

(57) [Claims] 1. An electrolytic cell filled with semiconductive fine particles containing titanium oxide is provided between an anode and a cathode and a light source, and a liquid to be treated having a metal component and an organic component is supplied into the filled fine particles. A water treatment apparatus, characterized in that a direct current is passed between both electrodes of the electrolytic cell while shining light to recover the metal components in the liquid to be treated and decompose the organic components. 2. The water treatment apparatus according to claim 1, wherein the fine particles are titanium oxide having oxygen defects. 3. The water treatment apparatus according to claim 1, wherein the fine particles are rutile type oxides in which tantalum and / or niobium are mixed in titanium. 4. The water treatment apparatus according to claim 1, wherein the light source is an ultraviolet lamp, and the electrolytic cell is made of an ultraviolet transparent material.