JPS5933004B2 - Electrodialysis method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a novel electrodialysis method, particularly in the operation of an electrodialysis desalination device using an ion exchange membrane, which allows a higher concentration rate to be obtained with a relatively small device without reducing dialysis efficiency. Regarding possible electrodialysis methods.

Electrodialysis, in which a large number of cation-exchange membranes and anion-exchange membranes are arranged alternately between a set of anodes and cathodes to concentrate or desalinate an electrolyte solution under direct current, is an example of plating. Various applications have been developed, including treatment and regeneration of flush water and desalination of seawater, and many of them have already been put into practical use.

Although there are various types of electrodialysis methods of this type, each method has its advantages and disadvantages, and none of them are superior in equipment, cost, or efficiency.

A typical conventional electrodialysis desalination method will be explained with reference to FIGS. 1 to 3. The method shown in FIG. 1 is a batch type or a batch type.

In this case, a certain amount of the raw wave processing solution is flowed from the raw wave processing solution storage tank R to the dilution chamber A of the dialysis tank, where it comes into contact with the concentrated liquid that has been flowed from the concentrated liquid storage tank C to the concentration chamber B of the dialysis tank. The water is electrodialyzed and desalinated, returned to the original storage tank R, and recovered as treated water S.

Such a method is suitable for small-scale operation and has high desalination efficiency, but the current flowing through the tank fluctuates widely.

It also operates intermittently and requires a large storage tank.

The method shown in Figure 2 is called the internal circulation continuous method.
The raw wave processing solution Q is continuously supplied to the solution tank R and sent to the dilution chamber A.

On the other hand, the concentrated liquid tank C comes into contact with the concentrated liquid sent to the concentration chamber B and is desalted, a part of which is recovered as treated water S, and a part of which is returned to the raw wave processing solution tank R and added to the solution Q. and further subjected to dialysis treatment.

The concentrate is also continuously recycled.

This type of system is suitable for medium-sized or larger scales, allows continuous operation, and requires only a small raw water storage tank.

Furthermore, the dialysis current is also constant.

However, if the desalination rate is high, the desalination efficiency will be inferior.

Figure 3 shows a system called a transient flow multi-stage continuous type. In the figure, three dialysis tanks are connected, and the raw wave processing solution Q is continuously passed through the dilution chambers of the first, second, and third dialysis tanks. A, it is desalinated and recovered as treated water S, while the concentrated liquid sequentially passes through the concentration chambers B of three dialysis tanks from the same liquid tank C, and returns to liquid tank C.
used in circulation.

This method is suitable for large-scale operation, allows continuous operation, and has a constant dialysis current.

However, when increasing the desalting efficiency, the desalting efficiency is the same as that of the batch method, but the number of stages is required.

Various methods for improving the above three methods have been proposed, but in those methods, the lower limit of the electrolyte concentration in diluted water is generally around 300 ppm, although it is affected by the electrolyte concentration in the raw wave treatment solution, and it is not recommended to It is said that low concentrations cannot be used.

This is because the dialysis efficiency decreases due to an imbalance of substances such as electrolyte back-diffusion and water electroosmosis due to the difference in salt concentration between the concentrated solution and the desalted water.

Even when the recovered treated water or desalinated water is used as industrial water, it has a conductivity at the same level as tap water (at 25°C, the conductivity is 150-300μ0/cm, hereinafter referred to as TDS of 80-300μ0/cm).
In many cases, a water quality of about 1.50 ppm) is required.

Furthermore, when desalting is performed to make the water as good as tap water, the concentration of the concentrated liquid is high, and its reuse is often required.

Conventionally, even if electrodialysis was applied as a technology for desalting a treated liquid with a low electrolyte concentration, it was not economical or efficient, and the salt concentration in the concentrated liquid could not be reused. Ta.

As a result of various experiments and research aimed at providing an improved electrodialysis method that satisfies the above requirements, the present inventor found that if the salt concentration in the concentrated solution is 5000 ppm or less, the salt concentration in the desalinated water is 50 ppm. It has been experimentally confirmed that the following formula is followed to a certain extent, and the present invention has been achieved.

That is, although the amount of desalination per membrane unit area decreases as the concentration decreases, it is effective in terms of the use of recovered water, and the dialysis power efficiency does not change within the above concentration range.

Cτ−Ce−τ Here Cτ: Salinity concentration Co of desalinated water after dialysis time τ:
Salt concentration in the raw wave treatment solution e: A natural number: A constant determined by the dialysis tank applied voltage, temperature, liquid flow rate, and device characteristics τ: Residence time in the dialysis tank The present invention is based on this knowledge, and the present invention is based on this knowledge. Two or more electrodialysis tanks having a dilution chamber and a concentration chamber are connected, and the dialysis process is performed while circulating the liquid in each chamber of each dialysis tank. This system is characterized in that by passing the concentrated water through the dilution chamber in the next stage, a liquid with a relatively low salt concentration is desalted and a concentrated liquid with a higher concentration is obtained.

To explain the present invention in more detail with reference to FIG. 4 showing one embodiment, the present invention is provided with a cathode 1 and an anode 2, and a plurality of anion exchange membranes 7 and cation exchange membranes 8 are alternately provided between them, and an electrode chamber 3 is provided. , 4, two electrodialysis tanks I and II each having a concentration chamber 5 and a dilution chamber 6 are connected and used.

The continuously supplied raw wave processing solution Q is once stored in the same solution storage tank R, and then sent to the dilution chamber 6 of the first dialysis tank (2).

A certain amount of water is supplied in advance from the storage tank R to the storage tanks C1, C2, El, and E2 as needed.

The water in storage tanks E, , and E2 is filled with suitable salt (preferably Na).
2SO4 (non-electrolyzed salt) and 5000p
Keep the concentration around prn.

E. The electrode solution is supplied to the electrode chambers 3 and 4 of the first dialysis tank (2).

The liquid C1 is supplied to the concentration chamber 5 of the first dialysis tank I, and further to the dilution chamber 6 of the second dialysis tank.

The E2 electrode solution is supplied to electrode chambers 3 and 4 of the second dialysis tank.

The liquid C2 is supplied to the concentration chamber 5 of the second dialysis tank (2).

The combined solution is circulated in each chamber of the first and second dialysis tanks I and II to undergo dialysis treatment.

The electrolyte in the raw wave treatment solution Q sent from the storage tank R to the dilution chamber 6 of the first dialysis tank I is transferred to the dilution chamber, where it is desalted and diluted, and then sent to the treated water or desalinated water storage tank. It is recovered as treated water S.

On the other hand, the liquid C1 is transferred to the solution Q in the concentration chamber 5 of the first dialysis tank (■).
The liquid in this tank is also sent to the dilution chamber 6 of the second dialysis tank and undergoes dialysis treatment, and the salt therein is sent to the concentration chamber 5 of the second dialysis tank. The liquid is transferred to the liquid in the storage tank C2 and diluted.

The liquid C2 is concentrated in the concentration chamber of the second dialysis tank (2) and then taken out as a concentrated liquid U.

When the salt content in the electrode chamber becomes of a type or reaches a concentration that is unsuitable for continuing the electrodialysis process, this electrode solution is sent to C1 or C2 for treatment or to be disposed of separately. .

As a result, the solution in the concentration chamber is gradually concentrated, and the solution in the dilution chamber is gradually diluted.

Therefore, if the desalination amount of both dialysis tanks ■ and ■ is the same, storage tank C
Although the salt of No. 1 is concentrated in the first dialysis tank I, it is diluted in the second dialysis tank to keep its concentration constant.

Then, the salt content of the liquid in the storage tank C2 is concentrated, and the treated water in the storage tank is diluted.

Thus, according to the present invention, it is possible to desalinate even a raw wave treatment solution with a relatively low salt concentration without reducing dialysis efficiency, reuse the treated water as industrial water, and reuse the concentrated liquid. It becomes possible to concentrate up to a certain concentration.

Moreover, the scale of the second dialysis tank is approximately 10% of the scale of the first dialysis tank.
or less, which is advantageous because it is possible to increase the concentration rate with a relatively small device.

Although the case where two dialysis machines are used to perform two-stage dialysis treatment has been described above, the number of stages is not limited to two stages, and can be further increased depending on the purpose.

Next, examples of the present invention will be given.

Anion-cation exchange membrane (commercially available standard membrane, effective membrane area 2 d
rrj) were placed alternately between a platinum-plated hot titanium anode and a stainless steel cathode at 1% intervals.
Two electrodialysis tanks were constructed with a concentrating chamber, a diluting chamber, and an electrode chamber, and while the solution was being circulated in each chamber, electricity was applied to saline solutions of various concentrations as shown in the flow sheet in Figure 4. Perform dialysis.

Residence time in the first dialysis tank ■ is τ1, desalination rate is vl
Assume that the residence time in the second dialysis tank ① is τ2, and the desalination rate is v2.

Table 1 shows a comparative example of the scale of each dialysis tank based on experimental values when each dialysis tank is operated at the limiting current density and the capacity of the storage tank C1 is set to 1/10 of the dilution chamber flow rate.

From this result, according to the method of the present invention, by combining the second-stage dialysis tank with a size of 10% or less of the first-stage dialysis tank, dialysis efficiency can be avoided (relatively low concentration It will be appreciated that continuous desalination can be carried out at 100 mL and the concentrate can be concentrated to a concentration that can be reused.

It goes without saying that the present invention can be effectively used not only for desalination treatment of saline water, but also, for example, for treatment of waste liquid from metal plating.

Thus, the present invention can provide a truly effective method for this type of electrodialysis.

[Brief explanation of drawings]

Figures 1 to 3 are flow sheets showing typical examples of conventional electrodialysis methods, and Figure 4 is a flow sheet showing one embodiment of the method of the present invention. In Figures 1 to 4, A...... dilution chamber, B...
・・Concentration chamber, C・・Concentrate storage tank, Q・・・・
- Raw wave processing solution, R...Same solution storage tank, L...
...Treatment water (desalinated water) storage tank, El, E2...
・Electrode solution storage tank, C1, C2... Concentrated solution storage tank, S
... Treated water, U ... Concentrate. In Fig. 4, 1... cathode, 2... anode, 3... cathode chamber, 4... anode chamber, 5
...Concentration room, 6...Dilution room (desalination room)
, 7... Anion exchange membrane, 8... Cation exchange membrane.

Claims (1)

[Claims] 1 Two or more electrodialysis tanks having an electrode chamber, a dilution chamber, and a concentration chamber are connected, and the dialysis treatment is performed while circulating the liquid in each chamber of each dialysis tank, and the first stage or subsequent stages are performed. The concentrated solution passed through the concentration chamber of the dialysis tank is further passed through the dilution chamber of the next stage dialysis tank, thereby desalting the solution with a low salt concentration and obtaining a concentrated solution with a high concentration. Electrodialysis method.