JPS6124479B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for treating electrocoating waste liquid, and more specifically, to a method for purifying electrocoating paint waste liquid by ion exchange to maintain the electrocoating liquid at a specified performance. It is. A typical example of a conventional electrodeposition coating waste liquid treatment method will be explained based on the drawings. FIG. 1 is a flowchart showing the basic treatment system of the waste liquid treatment method. The electrodeposition coating liquid overflowing from the electrodeposition coating tank (hereinafter referred to as electrodeposition tank) A of the surface treatment line is received in a sub-tank B, and is circulated along the solid line by a pump (not shown).
E and F indicate an anion exchange tower and a cation exchange tower, respectively, and the anion exchange tower exchanges anionic impurities such as sulfate ions and chloride ions brought in from the pretreatment process, and converts them into sodium, aluminum, etc. The cationic impurities are ion-exchanged in a cation exchange tower. Thereafter, it is returned to the electrodeposition tank A via a heat exchanger (not shown). Further, if necessary, a portion of the electrodeposition paint is returned to the electrodeposition tank A from a bypass provided with a filter D. Composition of the liquid in electrodeposition tank A
The pH and liquid temperature are monitored by appropriate means and the pump is shut down when these fall within predetermined limits. When the ion exchange ability of the ion exchange resins E and F decreases, known regeneration operations such as backwashing, regeneration, and extrusion are performed to restore the ion exchange ability. In the backwashing process, etc., a large amount of pure water flows from the pure water tank M into the ion exchange towers E and F along the dotted line and is sent to the waste water tank I. In the applicant's operation example, the amount of resin in the anion exchange tower E shown in Fig. 1 is 1350, and after 2 hours of ion exchange treatment, the amount of resin is approximately 14 m ³ per hour.
Continue to flow pure water for 15 to 30 minutes. Since the amount of resin remaining in the ion exchange tower is less than 1350, the resin concentration will be diluted by recovery, water washing, and backwashing. Similarly, the cation exchange column is also diluted. Therefore, the diluted solution has too low a paint component to be used for electrodeposition coating, and furthermore, the paint component cannot be completely separated from the electrodeposition ion exchange tower, so the paint is not recovered and is drained with N. The current situation is that it is being processed. The concentration of paint components in the bath solution in electrodeposition tank A is diluted by moisture brought in from the material to be treated. Also, when the paint is used effectively as a coating film or when the paint is pumped out from the tank, the concentration of paint components in the bath is diluted, so the concentration of the solution replenished to the bath solution in electrodeposition tank A is also diluted. must be higher than the specified concentration in the tank. Therefore, when the electrodeposition tank A is replenished with the liquid recovered by extrusion with a large amount of aqueous liquid, the bath liquid overflows from the electrodeposition tank A. Therefore, in the past, paint was not actually collected. Another drawback of the conventional ion exchange purification method is that the waste liquid discharged from the waste water tank I during operations such as backwashing, extrusion and second water washing creates a pollution problem. In other words, due to the paint contained in the waste liquid,
The BOD, COD, SS, etc. are high, so even if wastewater is treated with apparatus N using a polymer flocculant exceeding the normal amount, the flocculation effect is small. Therefore, cloudy water is discharged every time the ion exchange resin is regenerated.
It causes pollution problems such as BOD, COD, SS and dirty color. Figure 2 is a recent flowchart of a method for treating electrocoating waste liquid using a reverse osmosis treatment device. In FIG. 2, the coating waste liquid is sent from the sub-tank B to the reverse osmosis treatment device G, and the permeated water separated from the coating waste liquid is sent to the washing tank (washing tank for electrocoated aluminum sash, etc.). In addition to the permeated water, industrial water is supplied to the washing tank to maintain a predetermined amount. The paint components separated from the paint waste liquid by reverse osmosis treatment are collected in a concentration adjustment tank J, and after being adjusted to a predetermined concentration, the paint components are transferred to an electrodeposition tank A.
Return to The washing water needs to be applied to the wastewater treatment facility N. In Japanese Patent Application No. 52-64022, the applicant of this patent discloses that when the exchange capacity of the electrodeposited ion exchange tower decreases, pure water is flowed through the ion exchange tower to extrude the paint components and obtain an aqueous liquid containing the paint components. Next, we proposed a method for treating electrocoating waste liquid, which consists of subjecting only the aqueous liquid to reverse osmosis treatment to recover paint components, and returning the recovered paint components to the conductive paint tank. According to this method, the paint-containing water discharged from the ion-exchange tower can be treated in a closed circuit at the stage of restoring the processing capacity of the ion-exchange tower, and paint components can be recovered from the paint-containing water. One drawback of this method is that since pure water is required to recover paint components, a pure water purification device must be installed in the wastewater treatment facility, which increases costs. In view of the above facts, the present invention aims to achieve the advantages of the above patent application without using pure water. The present invention applies ion exchange to the waste liquid from the electrodeposition coating tank when carrying out the electrodeposition coating method in which the treated material is electrocoated in an electrodeposition coating tank and then the treated material is washed with water in a water washing tank. In a method for treating electrocoating waste liquid that includes treatment in a tower, reverse osmosis treatment is applied to the paint-containing aqueous liquid discharged from the ion exchange tower to obtain a recovered electrocoat liquid and permeated water, When the exchange capacity of the ion exchange tower decreases, the permeated water is passed through the ion exchange tower to discharge the paint-containing aqueous liquid, and the recovered liquid of the electrodeposition paint is returned to the electrodeposition coating tank. Here, the electrodeposition tank and its sub-tank are collectively referred to as the electrodeposition coating tank. Hereinafter, the present invention will be explained based on the drawings. FIG. 3 is a processing system diagram that is an improved version of the conventional processing system shown in FIG. Normally, the paint-containing water overflowing from the electrodeposition tank A into the sub-tank B is passed through ion exchange towers E and F, and the paint-containing water from which impurities have been exchanged and removed is returned to the electrodeposition tank A. The electrodeposition coating liquid, in which water is brought into the electrodeposition tank A from an alumite sealing treatment device for the material to be treated or a hot water washing tank (not shown) disposed upstream of the electrodeposition tank A, is diluted. Water containing paint to prevent this dilution is applied to the reverse osmosis treatment device G. Reverse osmosis treatment equipment G
The permeated water separated from the paint-containing water (waste liquid from sub-tank B) by
The water is sent to the tank and reused as washing water. When recovering paint components from ion exchange towers E and F, part of the permeated water is collected in a receiver tank K along the dotted line, and when the ion exchange capacity decreases, it is sent to ion exchange towers E and F to remove the paint in the tower. Use as extrusion water to recover. The recovered paint-containing water is stored in a liquid receiving tank L, and adjusted in a concentration adjusting tank J to a concentration suitable for use in the electrodeposition tank A. If necessary, the permeated water stored in the receiving tank K may be sent to a concentration adjusting tank J to adjust the concentration of the electrodeposition coating liquid. The reverse osmosis membrane used in the reverse osmosis treatment in device G must be resistant to paint solvents. Such a reverse immersion membrane is preferably one in which the joints between the modules are chemically or mechanically treated to resist swelling and shrinkage caused by solvents. A considerable portion of the paint solvent is separated into permeate water, and more than 99% of the resin solids are separated into the recovered liquid. An example of the ratio of various components of the electrodeposition coating liquid mixed into permeated water is as follows. Resin solid content: 0.0003-0.07% Butyl cellosolve: 50-56.5% Methanol: 99-100% Isopropyl cellosolve: 68-75% Amine (total of triethylamine and dimethylamine: 70-77% The above percentages are included in the electrocoating waste liquid This is a value that compares the rate of mixing into permeated water by weight percentage based on the weight of the component.The solvent mixed at the above ratio is 50% of the permeated water.
It may weigh more than Since the permeated water obtained by reverse osmosis treatment to recover paint from ion exchange towers E and F contains a solvent, compared to the method of the previous application which uses pure water,
It is advantageous in the following respects. That is, when the resin solid content remaining in the ion exchange tower comes into contact with pure water, it gels and becomes difficult to recover. However, according to the present invention, gelation does not occur because a high concentration of solvent components is present in the permeate water. Furthermore, when the ion exchange resin is exposed to air and then comes into contact with pure water, resin solids adhere to the surface of the ion exchange resin, making it impossible to regenerate it. However, according to the present invention, since a highly concentrated solvent portion is present in the permeate water, gelation does not occur on the surface of the ion exchange resin. In order to restore the ability of the ion exchange resin to exchange and remove ions such as sulfate radicals, iron, chlorine, aluminum, etc., the anion exchange tower undergoes the known steps of water washing, backwashing, regeneration, extrusion, water washing, and displacement. will be held. According to the present invention, it is necessary to be able to recover paint components with permeated water before performing the water washing. The water washing may be performed with pure water or permeated water. Backwashing may be performed using permeated water, but it is preferable to use pure water. Extrusion and washing are performed with pure water. Next, in the cation exchange tower, it is necessary to recover paint components using permeated water before washing with water. Washing with water can be performed with permeated water or pure water. The paint-containing water is filtered before reverse osmosis treatment.
It is beneficial to remove dirt, dust, etc. By measuring the pH, specific resistance, or resin solid content concentration of the paint-containing water in the liquid receiving tank L, the paint concentration currently present in the ion exchange resin is estimated. As long as the paint is present in the ion exchange resin, it is preferable to collect the paint by passing the paint-containing water through a reverse osmosis device. The permeated water obtained by reverse osmosis treatment and sent from the receiving tank K is returned to the electrodeposition tank A after adjusting the components necessary for electrodeposition in a concentration adjustment tank J. When the exchange capacity of the ion exchange column decreases, the above series of operations is repeated again. Therefore, according to the present invention, paint components can be recovered very effectively in a completely closed system. An apparatus for carrying out the method according to the present invention includes an electrodeposition bath, a washing bath, a reverse osmosis treatment device that communicates with the electrolytic bath and/or the washing bath, and a valve provided at the bottom of the device. and an ion exchange tower in communication with each other. A specific example of the ion exchange column of the above apparatus is illustrated in FIG. 4 as reference numeral E(F). The main body of this ion exchange tower is a cylindrical tank that contains an ion exchange resin. Several viewing windows 2 are provided on the outer wall of the main body 1 so that the state of the bath liquid inside can be observed. A nozzle 3 for injecting water or a chemical solution for ion exchange resin is attached to the upper part of the main body. Similarly, a nozzle 4 for injecting paint is also installed. These nozzles 3 and 4 extend through the wall of the tank and are connected to a water sprinkler pipe 5. At the bottom of the tank, a floor section 6 that partitions the inside of the tank is connected to the inner wall of the tank. This floor part 6 is made of ion exchange resin (not shown)
It supports the bath and allows the bath liquid to flow down. Therefore, the floor section 6 is made up of a plurality of plates arranged one above the other and separated from each other in the horizontal direction. A chemical solution outlet 7 is provided at approximately the same level as this support bed, and a solution outlet 8 for regeneration is similarly provided. This exit 8
is opened and closed by a regeneration valve (not shown).
An outlet pipe 11 to which a recovery valve 9 and an air blowing valve 10 are attached is fixed below the support bed 8. The recovery valve 9 introduces and shuts off paint waste liquid to the reverse osmosis treatment device. A mesh enclosure cover 12 is provided at the bottom of the tank to prevent foreign matter from entering the outlet pipe 11. In the above-mentioned ion exchange tower, the levels of bath liquid and other materials are determined as follows. The ion exchange resin is filled to about half the height of the tank _h1 from the support plate 6. The height of the paint-containing water entering the tank during ion exchange purification is _h2 , which corresponds to the inlet of the paint water. Next, the height of the paint after some of the paint water is removed to recover the paint is, for example, 5 from the resin height _h1 .
Set at cm high h ₃ . Liquid detection tube 13 that monitors the bath liquid level so that it does not fall below this height.
is provided. The level of the bath liquid level when the permeated water is replenished during paint recovery is _h4 , and the height of the backwashing liquid is _h5 , and appropriate liquids are used to monitor each level. Install a detection tube. The above ion exchange tower is operated as follows. The bottom collection valve 9 is opened to drain the liquid to a height _h3 , and the end point is detected in the liquid detection chamber 13. next,
Permeated water is introduced from the water introduction nozzle 3 to a height h ₄ and the introduction is stopped by a liquid detection tube (not shown). Subsequently, the air introduction valve 10 is opened so that the air loosens the ion exchange resin and removes the paint from the resin. Then, the process returns to the beginning and the water contained in the paint is removed and subjected to reverse osmosis treatment. According to the ion exchange tower as described above, there is no need to pneumatically extrude paint-containing water within the ion exchange tower above the height of the ion exchange resin. That is, permeated water is passed through an ion exchange tower, and then the pressure of this permeated water pushes out paint-containing water from the bottom through a valve, and the extruded aqueous liquid is again subjected to reverse osmosis treatment to produce paint. is collected. As the reverse osmosis device, a spiral type, a fiber-like type, and a tubular type can be used. However, when collecting paint components, 23
Since it is necessary to withstand a pressure of about 28 Kg/cm ² , a foliated fiber type is preferred because it is difficult to expand and contract. Furthermore, since turbulent flow can be caused in the tube of the reverse osmosis device, there is an advantage that dirt is less likely to adhere to the semipermeable membrane. Furthermore, even if the paint adheres, it can be cleaned mechanically using a sponge hole or the like, so there is an advantage that the effectiveness of its use does not deteriorate even if a large amount of impurities are mixed into the paint-containing liquid. Examples of the present invention will be described below. Example The treatment system for electrocoating paint wastewater in this example was as shown in FIG. The operating conditions for the anion exchange tower are shown in the table below.

【table】

【table】 The following table shows the operation of the cation exchange tower.

[Table] In this example, the reverse osmosis membrane used was Type B7 manufactured by DuPont, and the electrodeposition coating liquid used was AL-700 manufactured by Honey Kasei (resin content: 13%). The proportion (permeability) of the paint components that escaped into the permeated water that passed through the reverse osmosis device relative to the components in the electrolytic solution was 100 parts as shown in the table below. The concentration of the solvent portion in the permeated water was approximately 18% (however, the concentration is a measured value).

【table】

[Table] When this permeated water was allowed to flow through the electrodeposition ion exchange column, no gelation of the resin component of the paint was observed in the column. As a result, the resin content of the paint was recovered at a high rate of 99.4%, and the ability of the ion exchange resin was also well recovered. The effects achieved by the present invention are as follows. (1) By eliminating paint components from wastewater from electrodeposition ion exchange purification equipment, BOD and COD in wastewater can be reduced.
value decreases. By completely eliminating the contamination of paint components into wastewater, the paint can be reused and losses are reduced. (2) By using the permeate water obtained from the reverse osmosis device to regenerate the ion exchange resin, the amount of pure water used is reduced compared to a method in which regeneration is performed using only pure water. (3) The effects of (1) and (2) above enable closed wastewater treatment. (4) Since the resin solid content of the paint does not gel in the ion exchange tower, the paint recovery efficiency is increased and the ion exchange resin is not wasted. (5) According to the present invention, paint components are removed from paint water without using a polymer flocculant, so problems associated with the use of polymer flocculants are eliminated.

[Brief explanation of the drawing]

Figures 1 and 2 are system diagrams showing a conventional method for treating electrocoating waste liquid, Figure 3 is a treatment system diagram according to a specific example of the present invention, and Figure 4 is a specific example of an ion exchange column. FIG. A...Main tank (electrodeposition tank), B...Sub tank, C...Pump, D...Filter, E...Anion exchange tower, F...Cation exchange tower, G...Reverse osmosis treatment device, H...Washing tank, I...Wastewater tank, J...Concentration adjustment tank, K...Receiving tank, L...Liquid receiving tank, M...Pure water tank, N...Wastewater treatment equipment, 3...
Pure water inlet, 4...Paint-containing water inlet, 5...Water pipe,
6... Support bed, 7... Chemical solution outlet, 8... Outlet during regeneration, 9... Recovery valve, 10... Air introduction valve.

Claims (1)

[Scope of Claims] 1. When carrying out an electrodeposition coating method in which a material to be treated is electrocoated in an electrodeposition coating tank and then the material to be treated is washed with water in a water washing tank, a method is adopted in which the In a method for treating electrocoating waste liquid that includes treating the waste liquid in an ion exchange tower, reverse osmosis treatment is performed on the paint-containing aqueous liquid discharged from the ion exchange tower to remove the recovered electrocoat liquid and permeated water. and flowing the permeated water through the ion exchange tower when the exchange capacity of the ion exchange tower decreases,
A method for treating electrocoating waste liquid, which comprises discharging an aqueous paint-containing liquid and returning the recovered electrocoat liquid to the electrocoating tank.