JPH05115879A - Treatment of dyestuff aqueous solution - Google Patents

Abstract

PURPOSE:To solve a defect that time and cost are required in the decolorization treatment of a dyestuff aqueous solution by the conventional active carbon adsorption treatment or hypochlorous ion addition treatment by replacing the relevant processes with an electrolysis treatment. CONSTITUTION:This dyestuff aqueous solution containing chloride ion is treated by applying current with an insoluble electrode. Active chlorine or hypochlorous ion is generated by anodic oxidation of chloride ion and the active chlorine or the like acts on a chromophore of a dyestuff to decompose and to decolor. The method is economical as addition of a reagent is unnecessary and does not need a posttreatment as there is no residue of the reagent. And if conc. of residual active chlorine after treatment by applying current is large, the active chlorine is decomposed by reduction treatment such as application of current or the addition of a reagent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating an aqueous solution containing a dye, and more particularly to a method for decolorizing an aqueous dye solution by electrolytic decomposition of a dye component in a waste dye solution.

[0002]

2. Description of the Related Art At present, various kinds of synthetic dyes of hundreds of kinds are synthesized, and natural dyes are also used. The dye has a chemical structure containing various functional groups and has high chemical stability. As a method of removing the dye component remaining in the dyeing waste liquid after dyeing using the dye, that is, a method of decolorizing the waste liquid, an activated carbon adsorption method or an oxidizing agent such as ozone or sodium hypochlorite is used. There is an oxidative decolorization method. The adsorptive decolorization method using activated carbon is extremely effective, but it has a drawback that it requires a large amount of activated carbon and requires high-temperature treatment to regenerate the activated carbon, resulting in a large apparatus and a huge cost.

Ozone treatment is considered to be carried out by reacting ozone with an unsaturated bond portion such as a chromophore of a dye to cleave and oxidize the unsaturated bond via an intermediate such as ozonide. .. Ozone has a high degree of oxidation, but some compounds do not decolorize depending on processing conditions or dye type. Further, since ozone is a gas and it is difficult to contact the solution efficiently, the efficiency of the solution treatment may not be sufficient, and ozone may be toxic and may be dangerous during the treatment. The method of adding an aqueous solution of sodium hypochlorite is generally used because it is a simple treatment method, but it takes a long time to decolorize, and the amount thereof is likely to be excessive. Since various dyes are mixed in the treatment of the dye waste liquid, the amount of the aqueous sodium hypochlorite solution and the decoloring time differ depending on the type of the dye, so that this decolorizing step is always managed manually. Further, since the sodium hypochlorite aqueous solution contains an excessive alkali for preventing the decomposition of hypochlorite ions, it is necessary to neutralize the treated water before discharging.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the various drawbacks of the conventional methods for treating an aqueous dye solution and to provide a method for treating an aqueous dye solution which has good decolorization efficiency and does not require complicated maintenance and can be carried out at a low cost. And

According to the present invention, active chlorine and / or hypochlorite ions are produced by electrolyzing an electrolytic solution using a dye aqueous solution containing chloride ions as an electrolytic solution and using an insoluble electrode. A method for treating an aqueous dye solution, which is characterized in that the aqueous dye solution is treated with the active chlorine and / or hypochlorite ion, and a high concentration of available chlorine such as active chlorine is further added to the aqueous dye solution after the treatment. If residual hypochlorite ions remain, a reduction treatment is carried out to decompose the available chlorine.

The present invention will be described in detail below. When a dye aqueous solution containing chloride ions is treated by the method of the present invention, chloride ions present in the dye aqueous solution are oxidized at the anode to generate active chlorine, and the active chlorine is generated or at the cathode by ordinary water electrolysis. It is presumed that the chromophore of the dye is oxidatively decolorized by the oxidizing power of the hypochlorite ion formed by the reaction of the generated hydroxyl ion and the active chlorine, and the decolorization efficiency by the aqueous dye solution treatment according to the method of the present invention. Is superior to the conventional decolorization efficiency by adding an aqueous solution of sodium hypochlorite. Not only is the oxidizing power of active chlorine generated on the anode superior to that of sodium hypochlorite,
By contacting with hypochlorite ion or active chlorine on the anode also a chromophore that is difficult to be oxidatively decolorized even when contacting with sodium hypochlorite in a solution by directly oxidizing the dye on the anode It is presumed that it is easily decolorized.
It is also presumed that the chromophore having an unsaturated bond of the dye is reduced and decolored on the cathode.

The chloride ion used in the present invention is not particularly limited, and examples thereof include sodium chloride, calcium chloride, ammonium chloride and potassium chloride.
These chloride ions are converted into active chlorine or hypochlorite ion by electrolytic treatment, and then the active chlorine or hypochlorite ion reacts with the dye and returns to chloride ion again.
Therefore, the chloride ion concentration in the aqueous dye solution may be considerably low as long as the reaction between the active chlorine or hypochlorite ion generated on the anode and the dye occurs rapidly,
When it takes time to react the dye with chloride ion, it is desirable to increase the concentration of the chloride ion to accelerate the reaction rate with the dye, and the chloride ion concentration in the dye aqueous solution is generally 0.5. g / liter or more, preferably 5
g / liter or more. When the chloride ion concentration in the aqueous dye solution decreases, the concentration diffusion rate is controlled, and the production efficiency of active chlorine or hypochlorite ion decreases. In the aqueous dye solution to be treated, the chloride ion may be contained, for example, as a residue of the chloride ion added in the dye synthesis step. If the chloride ion concentration is within the above range, further chloride is added. It is not necessary to add ions, but when chloride ions are not contained at all or when the content is insufficient, the chloride ions are added before the energization (electrolysis) treatment.

The dye aqueous solution containing such chloride ions is subjected to an electric current treatment to decolor the dye aqueous solution. The various conditions of the energization treatment cannot be uniquely determined depending on the chloride ion concentration, the dye concentration, the type of dye, and the like. For example, the anode current density is about 0.5 to 20 A / dm ² , and the liquid temperature is 5 to 5. 40 ° C
Generally, it is set as a degree. If the liquid temperature is too low, the generation efficiency of active chlorine or hypochlorite ion will decrease, and if it exceeds 40 ° C, the self-decomposition of active chlorine or hypochlorite ion will start and the decolorization efficiency will decrease. Therefore, it is desirable to heat in winter and cool in summer. What is most needed to maintain the optimum conditions when the type of dye, that is, the type of chromophore, is to select the catalyst for the electrode coating, which may greatly change the decolorization efficiency. The electrodes used will be described in detail.

The conductive substrate of the anode of the insoluble electrode used in the present invention is iron, nickel, titanium, tantalum, niobium,
It is zinc or an alloy thereof, and is appropriately selected depending on the type of dye and the liquidity of the dye aqueous solution. The shape of the electrode substrate is
Plate shape, expanded metal, punching metal, wire mesh,
It can be of any shape, such as a cord-shaped wire. Furthermore, expanded metal, punching metal, wire mesh, blind wire, metal fiber laminated body, metal fiber woven cloth, wire roll, metal felt, sintered metal porous body, etc. are attached to a plate-shaped substrate by a known method such as bolting or welding. It is also possible to use an electrically bonded product as the electrode substrate. These may be laminated in a plurality of layers in consideration of the strength of the electrode base body and the amount of electricity supplied. A substrate obtained by nitriding, borating or carbonizing the surface of the electrode substrate can also be used as the electrode substrate and can be appropriately selected in consideration of the composition of the electrolytic bath and the like. For the nitriding treatment and the like, known methods such as ion plating and sputtering can be adopted. Providing an intermediate layer of an oxide or a platinum group metal of at least one metal selected from titanium, zirconium, niobium, tin, antimony, tantalum, etc. between such an electrode substrate and an electrode coating described later to extend the electrode life. You can also It is sufficient that the intermediate layer coating has a thickness of 10 μm or less, preferably 5 μm or less. If the coating of the intermediate layer is too thick, the electrolytic voltage will rise and the cost will increase.

The method for coating the intermediate layer is such that the salts of these component metals are dissolved in a soluble solution, coated and thermally decomposed in an oxidizing atmosphere or a reducing atmosphere to precipitate the target oxide or metal. Known methods such as a decomposition method, a sputtering method, a chemical vapor deposition method, an electroplating method, and a chemical plating method can be applied, and are appropriately selected according to the purpose. The substance constituting the electrode coating (catalyst) directly coated on the intermediate layer or on the substrate is a platinum group metal or a platinum group metal oxide or titanium, zirconium, niobium, tin, antimony, tantalum or cobalt. , Composite materials containing one or more metal oxides of base metal elements such as silicon are used. As the coating method, the same method as the intermediate layer coating,
That is, known methods such as a thermal decomposition method, a sputtering method, a chemical vapor deposition method, an electroplating method, and a chemical plating method can be applied.
If necessary, in the case of a thermal decomposition method, the above-mentioned coating forming means may be repeated, or in other methods, the amount of current supplied, the coating time, etc. may be controlled to obtain an electrode coating having a desired thickness. Besides this, a ferrite electrode or a lead-based electrode can also be used. The ferrite electrode can be obtained by a known method in which Fe ₂ O ₃ is the main component, various metal oxides having a valence of 1 to 5 are added thereto, and the sintering is performed. Examples of the added metal include manganese, iron, cobalt, nickel, copper, zinc and the like, and the metal preferably has a spinel structure. The shape of the ferrite electrode can be a round bar or a square plate, and the thickness of the electrode is about 3 to 12 mm. Since this ferrite electrode has a high electric resistance in the electrode, the shape, the electrode size, the thickness of the electrode coating, and the like are appropriately determined in consideration of the amount of energization.

Examples of lead-based electrodes include lead dioxide electrodes, lead or lead alloy electrodes, and the like. The lead dioxide electrode is a low-cost electrode with high oxygen overvoltage and unique anodic catalytic ability and high corrosion resistance, but it has a problem that it has a problem of bondability and cracks easily occur. The problem can be solved by providing or electroplating the lead dioxide coating with a dispersant to alleviate the internal strain. The lead alloy electrode is less worn than the lead dioxide electrode, and the eluted lead ions that cause sludge formation react with chloride ions in the electrolytic solution to form insoluble lead chloride, so the lead ions are not eluted into the solution. Can be prevented. In addition, there is a graphite electrode, which disappears as carbon dioxide gas or carbonate ions when oxygen is generated, but in the present invention, the anode reaction is a chlorine generation reaction and is hardly consumed. Can be used for any purpose. In the present invention, active chlorine or hypochlorite ion is electrolytically generated in the anode as described above, and the active chlorine or the like causes oxidative decomposition of the chromophore of the dye to decolorize the aqueous dye solution. On the other hand, the material of the cathode is not particularly limited as long as it has corrosion resistance to the aqueous dye solution, and examples thereof include graphite, aluminum, iron, nickel, titanium, tantalum, zirconium, lead, alloys thereof, or platinum group metals or oxides thereof. A coated product can be used.

When a dye aqueous solution is treated by using these electrodes and the above dye reacts rapidly with active chlorine, etc., as described above, the chromophore of the dye in the dye aqueous solution is decomposed to cause decolorization of the dye aqueous solution. Done. When the reaction of the dye with active chlorine or hypochlorite ion is slow, the active chlorine or the like may accumulate and remain in the dye aqueous solution after the treatment. The active chlorine and the like have a sterilizing power due to their strong oxidizing power, and may destroy the ecosystem of the natural environment, and it is desirable to reduce the concentration of the active chlorine and the like. When the decolorized dye aqueous solution is further treated with activated sludge, the concentration of active chlorine or hypochlorite ion in the treated dye aqueous solution must be zero. In order to remove the active chlorine and the like, it is desirable to carry out a reduction treatment, and as the reduction treatment, addition of chemicals such as ozone, thiosulfate and hydrosulfite, or electrolytic reduction is effective. In ozone reduction, residual ozone is decomposed quickly with chloride ion and oxygen as a product, and when thiosulfate such as sodium thiosulfate is used, the reduction product is sodium sulfate which is not a problem even if it is contained in wastewater. Also, hydrosulfite is an inexpensive and highly reducing agent. Furthermore, in the case of electrolytic reduction, the surface area of the cathode to be reduced is large and can be easily achieved by using, for example, a porous cathode. In the case of this electrolytic reduction, addition of reagents is unnecessary and no residue is generated. Therefore, it is particularly useful.

There are cases in which various metals and metal oxides that are catalysts used in dye synthesis remain in the aqueous dye solution and these metals and the like are contained in the waste dye solution. These metals, particularly metal ions such as manganese and iron, are deposited as an oxide on the anode to inhibit the production of active chlorine and reduce the decolorization efficiency. In order to prevent a decrease in this decolorization efficiency, a solution containing active chlorine or hypochlorite ions generated by electrolysis is mixed in advance with a solution containing metal ions to oxidize these metal ions, and then an electrolyte solution is prepared. do it.

[0013]

EXAMPLES Next, examples of decolorizing treatment of dye aqueous solution by the method of the present invention will be described, but the present invention is not limited thereto. Electrode samples were prepared as follows prior to decolorization of the aqueous dye solution. Electrode Sample 1 A commercially available titanium plate having a length of 100 mm, a width of 100 mm and a thickness of 3 mm was degreased with acetone, washed with a hot oxalic acid solution, further washed with pure water and dried to obtain an electrode substrate. A solution of tin chloride and niobium chloride dissolved in ethanol at a molar ratio of 1: 1 was applied to the electrode substrate, dried, and then baked at 550 ° C. for 10 minutes. This operation was repeated to form an intermediate layer coating having a thickness of 3 μm. Next, iridium chloride, platinum chloride and palladium chloride are dissolved in butanol solution and the molar ratio of each metal is 4: 1: 1.
Was prepared. The solution was applied onto the substrate coated with the intermediate layer, dried, and baked at 550 ° C. for 10 minutes. Repeat this operation to form an electrode coating with a thickness of 15 μm.
And

Electrode Sample 2 A commercially available titanium plate having a length of 100 mm, a width of 100 mm and a thickness of 3 mm was subjected to sandblasting, and then immersed in an aqueous sodium hydroxide solution at about 80 ° C. for 2 hours for degreasing. 5% after washing
Immersion in a hydrofluoric acid aqueous solution, washing with water, and immediately, a 1 μm platinum plating layer was formed using an ammonium phosphate and sodium phosphate bath containing chloroplatinic acid. The titanium plate coated with the platinum plating is used as an electrode substrate and is electrolyzed in a lead dioxide electrodeposition bath in which lead nitrate is dissolved at a temperature of 50 ° C. and a current density of 4 A / dm ² using stainless steel as a cathode, and coated with lead dioxide. A lead dioxide electrode having a layer thickness of 0.6 mm was prepared and used as sample 2.

[0015]

Example 1 An electrode sample 1 was used as an anode, a lead plate having the same size as the anode was used as a cathode, and a yellow dye waste liquid containing mainly an azo dye-based acid mordant dye (containing about 5% sodium chloride) 1
A direct current of 10 A was applied for 1 hour while stirring at room temperature using 1 liter of the electrolytic solution.

Comparative Example 1 To 1 liter of the same dye waste solution as in Example 1 was added 150 ml of a commercially available 12% aqueous sodium hypochlorite solution, and the mixture was stirred at room temperature for 1 hour.

[0016]

Example 2 Electrode sample 1 was used as an anode, and stainless steel SUS304 having the same size was used as a cathode. Sodium chloride was added to a green dye waste liquid mainly containing anthraquinone vat dye to prepare a solution having a sodium chloride concentration of 10%. The solution contained about 300 ppm manganese ions. 1 liter of the dye waste liquid (Example 2-1) and separately the dye waste liquid 1
To the liter, the solution decolorized in Example 1 (Example 2-2) was added.
A liquid to which 100 ml of a direct current was applied for 10 minutes at 20 A / dm ² was added to each of the solutions to which a direct current of 20 A was applied for 1 hour while stirring at room temperature.

[Comparative Example 2] Commercially available 12
% 300% aqueous sodium hypochlorite solution was added, and the mixture was stirred at room temperature for 1 hour.

[0017]

Example 3 A lead-tin (5%) plate having a length of 100 mm, a width of 100 mm and a thickness of 5 mm was used as an anode, and graphite of the same size was used as a cathode, and an orange dye waste liquid (about 3 % Of sodium chloride) was used as an electrolytic solution, and a DC current of 5 A was applied for 30 minutes while stirring at room temperature.

Comparative Example 3 To 1 liter of the same dye waste solution as in Example 3 was added 50 ml of a commercially available 12% aqueous sodium hypochlorite solution, and the mixture was stirred at room temperature for 30 minutes.

[0018]

Example 4 A lead dioxide electrode of electrode sample 2 was used as an anode, a platinum-plated titanium plate of the same size was used as a cathode, and sodium chloride was added to a blue dye waste liquid mainly composed of anthraquinone-based vat dye to give a sodium chloride concentration of 4 % Aqueous solution was prepared, and 1 liter of the aqueous solution was used as an electrolytic solution, and a direct current of 10 A was applied at room temperature for 2 hours with stirring.

Comparative Example 4 To 1 liter of the same dye waste solution as in Example 4 was added 300 ml of a commercially available 12% aqueous sodium hypochlorite solution, and the mixture was stirred at room temperature for 2 hours. Table 1 shows the results of colorimetry and the state of precipitation after electrification for each of the electrolytes (dye waste liquid) of Examples 1 to 4 and Comparative Examples 1 to 4 before and after energization were collected in a colorimetric tube. I summarized it in.

[0019]

[Table 1]

Further, Table 1 shows the results of measuring the residual effective chlorine concentration of the electrolytic solution (dye waste solution) after energization by iodometric titration with sodium thiosulfate. A reduction treatment was carried out by passing a direct current through the electrolytes of Example 1, Comparative Example 1, Example 3 and Comparative Example 3 through a ferrite anode and a graphite cathode having an area ratio of 1:10 (anode current density 5 A / dm. ² , cathode current density
0.5 A / dm ² ). Further, the required amount for the electrolytic solution of Example 2-1, Example 2-2, Comparative Example 2, Example 4 and Comparative Example 4 (the amount calculated to be necessary for reducing residual available chlorine from the analysis results) ) Sodium thiosulfate was added to perform reduction treatment. Table 1 shows the measured values of the residual available chlorine concentration in the electrolytic solution after each reduction treatment. From Table 1, it can be seen that the liquid obtained by the electric current treatment using the insoluble electrode of the aqueous dye solution has a higher degree of decolorization (the liquid color is lighter) than the liquid obtained by the treatment with hypochlorous acid and precipitates. Further, it is also understood that effective chlorine remaining after the energization treatment can be significantly reduced (energization treatment) or reduced to almost zero (sodium thiosulfate addition treatment) by performing reduction treatment.

[0021]

INDUSTRIAL APPLICABILITY The present invention produces an active chlorine and / or hypochlorite ion by electrolyzing an electrolytic solution using an aqueous solution of a dye containing chloride ion and an insoluble electrode. A method for treating an aqueous dye solution, which comprises treating the aqueous dye solution with chlorine and / or hypochlorite ions. Chloride ions are contained in the aqueous dye solution electrolytically treated according to the present invention, and by electrolytically oxidizing the chloride ions, the chloride ions are oxidized to active chlorine, and the active chlorine is converted to hydroxide ions. Reacts to produce hypochlorite ions. The active chlorine or hypochlorite ion reacts with the dye component on the anode and reacts with an unsaturated bond portion such as a chromophore to cleave and oxidize the unsaturated bond, whereby decolorization is performed.

This method of the present invention is inexpensive because the dye aqueous solution can be treated without using a reagent, the operation is stable, and no post-treatment or regeneration of the added reagent is required, which is troublesome. It can be controlled easily without hanging. Moreover, unlike the conventional treatment with hypochlorite ion, active chlorine or hypochlorite ion generated by electrolysis reacts with the dye component on the surface of the anode, so that the decomposition of the dye component is promoted and the decolorization efficiency is greatly improved. When an intermediate layer made of a platinum group metal or titanium is formed between the electrode base of the insoluble electrode and the electrode coating, the adhesion between the electrode base and the electrode coating is improved, the electrode life is extended, and the aqueous dye solution is treated for a long period of time. It will be possible to do. Then, in the decomposition of the dye component by this electrolytic oxidation, it is necessary to adjust the initial addition amount of chloride ion according to the slow reaction rate of the dye component and active chlorine, etc. The concentration of residual available chlorine in the dye aqueous solution after decomposition becomes high. In this case, further reduction treatment by energizing or adding chemicals is performed to decompose the residual available chlorine (conversion to chloride ion).
The residual effective chlorine concentration can be reduced to zero or significantly to prevent environmental pollution.

Claims (3)

[Claims] 1. An active chlorine and / or hypochlorite ion is produced by electrolyzing an electrolytic solution using a dye aqueous solution containing chloride ions as an electrolytic solution and using an insoluble electrode.
A method for treating an aqueous dye solution, which comprises treating the aqueous dye solution with the active chlorine and / or hypochlorite ion. 2. The method of claim 1, wherein the insoluble electrode comprises an electrode substrate, an intermediate layer formed on the electrode substrate, and an electrode coating formed on the intermediate layer. 3. An active chlorine and / or hypochlorite ion is produced by electrolyzing the electrolyte solution using an aqueous solution of a dye containing chloride ions as an electrolyte solution and using an insoluble electrode.
A method for treating an aqueous dye solution, which comprises treating the aqueous dye solution with the active chlorine and / or hypochlorite ion, and further reducing the aqueous dye solution to reduce the residual available chlorine concentration.