JPH0550062A - Purifying method for aqueous solution - Google Patents

Abstract

PURPOSE:To provide a precoating method which improves the quality of treated water and prolongs the life of a precoating material. CONSTITUTION:A powder ion exchange resin (a) and ion exchange fibers (b) consisting of a polyacrylic ion exchange polymer having a carboxyl group and a polymer for reinforcement are used as the precoating material in this method for purifying an aq. soln. with a precoated filter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing impurities contained in water or waste water in nuclear power plants, thermal power plants, pharmaceutical companies, etc., and more particularly to a method for purifying an aqueous solution using a precoat filter. Is.

[0002]

2. Description of the Related Art Conventionally, a powdery ion exchange resin has been used as a precoat material in a precoat type filter for purifying water or wastewater in a nuclear power plant or a thermal power plant. Precoat filtration is a precoat material on some kind of support, which forms a filtration layer with a certain thickness.
It is a general term for methods of removing impurities contained in water to be treated by passing through the layer. Recently, there is a method of pre-coating a powder ion-exchange resin on a support element by water pressure, and passing water to be treated through the layer for purification.
The device is called a precoat filter.

This precoat material is backwashed and replaced with a new precoat material when the differential pressure during passage of water reaches a certain value. However, in many cases, the specified differential pressure is reached before the ion exchange capacity of the precoat material is used up effectively,
At the time of backwashing, the differential pressure was controlled.

Particularly in a nuclear power plant, all the waste pre-coated materials which are backwashed and recovered are stored and stored because they contain radioactive substances, and the ever-increasing measures for them have been raised as a new social problem.

Therefore, for the purpose of reducing waste, it has become necessary to extend the period until backwashing after precoating (the water sampling life of one precoating material) as long as possible.
This does not mean that the differential pressure rise of the precoat material can be prevented and the water sampling life can be extended, and it does not make sense unless the quality of the treated water is equal to or higher than that of existing materials.

If it becomes possible to improve the quality of treated water, it is also effective in greatly reducing the radiation exposure of workers of nuclear power plants.

As a method corresponding thereto, improvement of the precoat material is considered, and use of ion exchange fiber as the precoat material has been devised (Japanese Patent Laid-Open No. 55-6738).
4).

[0008]

However, these ion-exchange fibers have not been able to achieve the above-mentioned object, because they have an effect that the precoat material does not physically generate cracks.

In order to prolong the life of the precoat practically, it is required that the precoat layer composed of the ion exchanger has an appropriate porosity and is not consolidated when passing water.

However, if the precoat material is swollen too much to prevent consolidation, ions will leak and the quality of the treated water will be extremely deteriorated. Therefore, it is not preferable to mix the precoat material itself having no ion-exchange performance, and it is therefore essential that the powder-ion-exchange resin is ion-exchange fiber.

At this time, the ion exchange fiber is required to have elasticity to water pressure and good hydrophilicity and wettability to some extent.

An object of the present invention is to provide a method for purifying an aqueous solution which solves the drawbacks of the prior art, prolongs the filtration life of the precoat, and improves the quality of treated water as compared with the conventional method. Is.

[0013]

That is, the present invention has the following configuration.

In the method for purifying an aqueous solution with a precoat filter, a powder ion exchange resin (a) as a precoat material and an ion exchange fiber (b) composed of a polyacrylic ion exchange polymer having a carboxyl group and a reinforcing polymer are used. A method for purifying an aqueous solution, which is used.

The present invention will be described in detail below.

The ion exchange fiber (b) used in the present invention is
It is characterized by the fact that it is a fiber composed of a polyacrylic ion exchange polymer having a carboxyl group and a reinforcing polymer, and has good wettability of acrylic in water, swelling property, elasticity against compression, and fiber strength due to the effect of the reinforcing polymer. Therefore, the precoat layer can be effectively prevented from being consolidated. The mixing mode of the ion-exchange polymer and the reinforcing polymer is not particularly limited, but for example, a core-sheath fiber containing an ion-exchange polymer as a main component of a sheath component and a reinforcing polymer as a core component, a multi-core mixed and a multi-core composite It is preferable that the fibers have sufficient mechanical strength, are effective in preventing consolidation, and have a large specific surface area as an ion exchanger.

Further, even if another polymer is used as a reinforcing material in blend spinning or the like, it does not depart from the gist of the present invention.

If the proportion of the reinforcing polymer in the ion exchange fiber (b) is too small, the mechanical strength will be weak, and conversely, if it is too large, the ion exchange capacity and the adsorption amount will decrease, so that it is preferably 10 to 10. 70%, and more preferably 20 to 50%.

As the reinforcing polymer, poly-α is used.
Any material such as olefin, polyamide, polyester, polyacryl can be considered, but polyacryl is preferable from the viewpoint of ease of production. In addition, since it is treated with acid and alkali when it is made into an ion-exchange fiber, it is necessary to have some acid resistance and alkali resistance.

The method for producing the ion-exchange fiber in the present invention is arbitrary, but specifically, a solution in which a specific alkali metal hydroxide aqueous solution and a cross-linking agent are mixed after forming polyacrylonitrile into a required form A method for producing a core-sheath type ion-exchange fiber in which polyacrylonitrile having a carboxyl group by selectively hydrogelating the fiber outer layer portion to have polyacrylonitrile as the fiber inner layer portion is caused by the action of.

Examples of the alkali metal hydroxide used for this purpose include hydroxides of alkali metals such as Na, K and Li, or a mixture thereof. As the cross-linking agent, generally known formalin, hydrazine, hydroxylamine and the like can be used. It is preferable that the crosslinking treatment and the hydrolysis are performed at the same time. That is, an aqueous solution in which the crosslinking agent and an alkali metal hydroxide are allowed to coexist is prepared,
The fibers are dipped and heated to the reaction temperature for crosslinking treatment and hydrolysis. In that case, the most important thing is not to reduce the fiber physical properties of the base acrylic fiber as much as possible.

The ion exchange fiber has a diameter of 15 to 15 from the viewpoint of having a high specific surface area and preventing consolidation of the precoat layer.
100 μm is preferable. More preferably 15-50 μ
m, particularly 15 to 30 μm (dry state) is most preferable.

The fiber length is preferably 0.1 to 1 mm for the purpose of maintaining an appropriate porosity of the precoat layer. More preferably, 0.15-0.6 mm, especially 0.2-0.
4 mm is most preferred.

As the cross-sectional shape of the fiber, various shapes such as a circular star shape, a flat shape, and a triangle shape are used, and there is no problem.

The powder ion exchange resin used in the present invention preferably has a particle size of 1 to 250 μm, more preferably an average particle size of 60 μm or less. Specifically, powders of styrene-divinylbenzene copolymers with excellent chemical stability and ion-exchange performance, ion-exchange resins with ion-exchange groups introduced or ion-exchange resins composed of acrylic acid monomer-divinylbenzene copolymers can be used. The thing crushed can be mentioned.

The ion exchange group of the powder ion exchange resin in the present invention means an anion exchange group and a cation exchange group.

As the anion-exchange group, a strongly basic anion-exchange group obtained by treating a haloalkylated product with a tertiary amine such as trimethylamine, and a secondary or lower amine such as isopropylamine, diethylamine, piperazine or morpholine. Examples of the weakly basic anion-exchange group obtained by the treatment include strong basic anion-exchange group from the viewpoint of treatment performance in the present invention.

As the cation exchange group, a sulfonic acid group,
An aminocarboxyl group such as a phosphonic acid group, a carboxyl group or an iminodiacetic acid group is preferably used, but a sulfonic acid group is more preferable from the viewpoint of processing performance in the present invention.
However, when the volume of the waste precoat material is reduced by incineration, there is a problem of damage to the incinerator by SO _x gas, and it is necessary that the material be a carboxyl group.

Here, the combination of the ion exchange fiber and the powder ion exchange resin as the precoat material in the present invention is:
[Fc, Ra] and [Fc, Rc, Fa] are possible, but [Fc, Rc, Ra] is most preferable because it is important to improve the quality of treated water especially for purification of wastewater for nuclear power plants. Where Fc is the cation exchange fiber of the present invention, Rc,
Ra means powder cation and powder anion exchange resin, respectively.

In the present invention, the ratio of the ion exchange fibers to the total amount of the precoat material is 10 to 6 in terms of dry weight.
0% is preferable. It is more preferably 15 to 50%, further preferably 20 to 40%. This is because when the fiber content is low, the effect is small in terms of the proper porosity of the precoat layer, the effect of preventing consolidation and the securing of a high specific surface area, and when the fiber content is too high, the porosity of the precoat layer becomes large and the pressure difference leads to a long life. This is because the quality of the treated water is inferior. The ratio of cation exchanger / anion exchanger in the precoat material of the present invention is preferably in the range of 1/10 to 10/1,
For the purification of waste water for nuclear power plants, 1/2 to 10/1 is preferable, and 1/1 to 10/1 is particularly preferable.

The method of use as the precoat material is arbitrary. For example, the powder cation / anion exchange resin and the ion exchange fiber are stirred and mixed in water to form a floc body, or the powder cation / anion exchange resin is stirred and mixed in water to form a floc body. After that, the ion-exchange fiber is mixed and stirred to form a floc body, which is a single-step precoating method by a normal method, a step (multi-stage) precoating method, or a powdered cation / anion exchange resin is stirred and mixed in water to form a floc body. Various combinations such as an overcoat precoating method of precoating and precoating ion-exchange fibers dispersed in water from above, or a body feeding method of precoating the element with the water to be treated and the precoat material at the same time are conceivable. However, from the point of view of operation and maintenance, the method of performing one-step precoating by a usual method is preferable. Further, a dispersant such as a surfactant may be added at the time of stirring and mixing.

As the pre-coated support used in the present invention, all conventional pre-coated filters such as cylindrical type and leaf-shaped type and normal-shaped filtration supports used for ion exchange filtration can be used. Can be applied as is to the method that is usually used today.

The thickness of the precoat layer is 2 to 20 mm.
It is about 3 to 10 mm. In the present invention, the passing speed of the aqueous solution to be treated through the precoat layer is about 1 to 20 m / hr, and the pressure loss is 1.5 to 2 k.
When it reaches about g / cm ² , it is backwashed by a usual method and the support is used repeatedly.

The precoat material using the ion-exchange fiber and the powder ion-exchange resin of the present invention has extended life and improved water quality as compared with the conventional precoat material. It has a thin precoated filtration layer, and has a strong structure that is formed as a whole by forming flocs of a powder ion-exchange resin having ion-exchange fibers at the core, and by mixing the ion-exchange fibers. Good wettability and swellability of polyacryl in water, elasticity by pressure loss and effect of reinforcing polymer keep strength, prevent compaction phenomenon when passing water, maintain porosity necessary for ion exchange or adsorption, and This is because the fibers themselves having a large specific surface area have a very effective ion exchange function, and therefore impurities (colloids such as clads and ions) in the aqueous solution to be treated can be taken in between the grains of the entire precoat layer without waste.

Examples will be shown below, but the present invention is not limited to these.

[0036]

【Example】

Example 90% acrylonitrile and 10% methyl acrylate
A spinning dope prepared by dissolving 10 parts of an acrylonitrile-based polymer consisting of 90 parts in a 48% aqueous solution of sodium thiocyanate was spun in the usual way, stretched 10 times and dried, and after crimping, 0.5 mm It was cut fiber. Next, 100% of an aqueous solution containing 25% of sodium hydroxide and 5% of hydrazine was adhered to this cut fiber, followed by treatment in steam at 110 ° C. for 30 minutes. Further, by activating with hydrochloric acid and then washing with water, a polyacrylic ion exchange fiber having a carboxyl group was produced (exchange capacity 4.1 meq / g-Na, fiber diameter about 20).
μm).

When the cross section of this fiber was observed with an electron microscope, it was confirmed that the outer layer portion was a polyacrylic layer having a carboxyl group and the inner layer portion was a polyacrylic layer having a core-sheath structure.

The exchange capacity was measured by the following method.

1 g of this cut fiber was placed in 50 ml of 0.1N sodium hydroxide and shaken for 2 hours to give 5 ml.
Accurately calculate and calculate by neutralization titration.

Commercially available powder cation exchange resin [“Powdex” -PCH (Organo Co.), having sulfonic acid group, exchange capacity 5.0 meq / g] and commercially available powder anion exchange resin [“Powdex” -PAO]. (Organo Co., Ltd.), having a trimethylammonium group and having an exchange capacity of 3.2 meq / g], the above ion-exchange fibers are mixed at a ratio of 30% of the total amount to give a cation / anion ratio. It was prepared so as to be a 6/1 floc body.

A column (50 mmφ) having an acrylic support plate inside was used, a filter paper was placed on the support plate, and the above-mentioned flocked body was deposited on the filter paper for precoating. The total amount of flocs was 1.96 g (about 1.0 kg / cm ² ). From the top, 8m of the prepared simulated solution containing 5ppm of amorphous iron (ferric hydroxide, average particle size 3.6μm) in terms of iron
Water was passed at a flow rate of / hr until the pressure difference of the precoat material at the nuclear power plant was determined to be 1.75 kg / cm ² , and the average iron content was measured from the filtration time (precoat life) and iron concentration. The removal rate was calculated. The results are shown in Table 1.

Comparative Example 1 A powder ion-exchange resin was prepared in the same manner as in Example 1 except that the ion-exchange fiber was not mixed, so that a floc body having a cation / anion ratio of 6/1 was prepared, and a precoat experiment was conducted. .. The results are shown in Table 1.

Comparative Example 2 The polystyrene fiber thus produced was cut into a length of 0.3 mm to obtain a cut fiber. 1 part by weight of the cut fiber was added to a commercially available crosslinking / sulfonation solution consisting of 7.5 parts by volume of primary sulfuric acid and 0.1 part by weight of paraformaldehyde.
The mixture was reacted at 0 ° C. for 4 hours, further reacted at 100 ° C. for 3 hours and then washed with water. Next, it was treated with alkali and then activated with hydrochloric acid to obtain a cation exchange fiber having a sulfonic acid group. (Exchange capacity 5.0 meq / g-Na,
(Fiber diameter: about 40 μm) However, this fiber is very fragile and powdered during the manufacturing process, which requires extremely careful handling at the laboratory level and was impractical. A similar precoat experiment was conducted. The results are shown in Table 1.

From these results, the effect of mixing the ion exchange fiber of the present invention in the condensate treatment works very effectively for suppressing the increase in the differential pressure of the precoat layer and improving the water quality of the water to be treated. It was found that the elasticity and strength against compression of and the appropriate water swelling property are more effective.

[0045]

[Table 1]

[0046]

EFFECT OF THE INVENTION In the method for purifying an aqueous solution according to the present invention, the ion-exchange fiber composed of the polyacrylic polymer having a carboxyl group and the reinforcing polymer serves as the core of the powder ion-exchange resin to form a flock body, and to form an appropriate void. Rate and compressive strength, the life of the precoat material is dramatically extended, and the excellent ion exchange performance of the fiber with a large surface area makes it possible to improve the quality of treated water. This is a very simple method that can use the ordinary precoating method as it is, and is very effective.

According to the present invention, the volume reduction of wastes of variously used precoat materials for water treatment is promoted, and the radiation exposure of workers concerned at nuclear power plants can be greatly reduced.

The liquid to be treated to which the present invention is applied is not limited but is applied to all liquids using a precoat filter, but is particularly effective for wastewater for nuclear power plants and thermal power plants. is there.

Wastewater from nuclear power plants and thermal power plants
Circulating system condensate, fuel pool water, demineralizer backwash wastewater, steam generation blow water, wet water separator drain water, cavity water, depression pool water, core water, etc. Shows excellent effects on the purification of.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Satoshi Ito 1 9-9 Oe-cho, Minato-ku, Nagoya-shi, Aichi Toray Industries, Inc. Nagoya Plant

Claims (1)

[Claims] 1. A method for purifying an aqueous solution with a precoat filter, comprising: a powder ion exchange resin (a) as a precoat material; an ion exchange fiber (a) containing a polyacrylic ion exchange polymer having a carboxyl group and a reinforcing polymer. ) Is used to purify the aqueous solution.