JPH0798187B2 - Aqueous solution purification method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for treating impurities contained in water or wastewater in nuclear power plants, thermal power plants, pharmaceutical companies, etc., and particularly uses a precoat filter. The present invention relates to a method for purifying an aqueous solution.

[Prior Art] Conventionally, in a precoat type filter for purifying water or wastewater in a nuclear power plant, a thermal power plant or the like, a powder ion exchange resin is used as a precoat material.
Precoat filtration is a general term for a method of forming a filtration layer having a certain thickness on a support with a precoat material and removing impurities contained therein by allowing the water to be treated to pass through the layer. There is a method in which a powder ion-exchange resin is pre-coated on a support element by hydraulic pressure and water to be treated is passed through the layer to purify it, and the apparatus is called a pre-coat filter.

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

Particularly in nuclear power plants, all the waste pre-coated materials that have been backwashed and collected contain radioactive substances and are therefore subject to storage and storage, and the ever-increasing measures for them have been raised as new social problems.

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

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

As a method corresponding thereto, improvement of the precoat material is considered, and it has been devised to use ion exchange fibers as the precoat material (Japanese Patent Laid-Open No. 55-67384).

[Problems to be Solved by the Invention] However, these ion-exchange fibers have not been able to achieve the above-mentioned object, because the effect is such that the precoat material does not physically generate cracks.

In order to extend 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. It is necessary for the ion-exchange fiber that has an appropriate porosity in water and an anti-consolidation property to exhibit a certain range of water content, but this point has not been mentioned so far.

Further, in order to improve the water quality, it is important that the ion exchanger constituting the precoat layer has a large specific surface area and an adsorption capacity for impurities, but the water content also greatly affects this.

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

[Means for Solving the Problems] That is, the present invention has the following configuration.

In a method for purifying an aqueous solution with a precoat filter, a powder ion exchange resin and an ion exchange fiber composed of an ion exchange polymer and a reinforcing polymer are used as a precoat material, and the water content of the ion exchange fiber composed of the ion exchange polymer and the reinforcing polymer is used. A method for purifying an aqueous solution, wherein the degree is 1.0 to 3.0.

Hereinafter, the present invention will be described in detail.

The form of the ion-exchange fiber used in the present invention is not particularly limited, and any ion-exchange polymer having a fiber form in the range of water content of 1.0 to 3.0 may be used. It is necessary that the fiber is composed of an ion exchange polymer and a reinforcing polymer in order to efficiently suppress the consolidation of the layer.

Here, the water content is a Na-type (Cl-type) cation (anion).
After sufficiently immersing the exchanger in ion-exchanged water, centrifugal dehydration was performed to remove surface water, and then the weight (W) was immediately measured, and the weight was immediately dried, and then the weight (W ₀ ) was measured to obtain the following formula. It is the value obtained from the above.

Moisture content = (W−W ₀ ) / W _{0 There} is no particular limitation on the mixing mode of the ion-exchange polymer and the reinforcing polymer. For example, a core-sheath containing an ion-exchange polymer as the main component of the sheath component and a reinforcing polymer as the core component. Mold fibers, multicore mixed and multicore composite fibers are preferably used. In particular, the multi-core type composite fiber is preferable because it has sufficient mechanical strength, is effective in preventing consolidation, and has a large specific surface area as an ion exchanger.

The ion exchange polymer is not particularly limited, and examples thereof include polymers obtained by introducing ion exchange groups into polystyrene type, polyacrylic type, polyamide type, polyester type, polyvinyl alcohol type, polyphenol type, poly-α-olefin type compounds and the like. it can. In particular, a polymer obtained by introducing an ion exchange group into a crosslinked and insolubilized polystyrene-based compound is preferable because it is excellent in ion exchange performance and chemical stability, which are extremely important in the present invention.

Further, examples of the reinforcing polymer include, but are not limited to, poly-α-olefin, polyamide, polyester, polyacrylic and the like. Among them, poly-α-olefins are preferable in the production of ion exchange fibers because they have excellent chemical resistance. Poly-α-olefins include, but are not limited to, polyethylene, polypropylene, poly-3-methylbutene-1, poly-4-methylpentene-1 and the like.

The diameter of such an ion exchange fiber is preferably 15 to 100 μm from the viewpoint of having a high specific surface area and preventing the precoat layer from being consolidated. It is more preferably 20 to 70 μm, and most preferably 30 to 50 μm (dry state).

The fiber length is preferably 0.1 to 1 mm for the purpose of maintaining an appropriate porosity of the precoat layer. More preferably from 0.15
Most preferably, it is 0.6 mm, particularly 0.2 to 0.4 mm.

As the cross-sectional shape of this fiber, various shapes other than a circular shape are used.

The powder ion exchange resin in the present invention preferably has a particle size of 1 to 250 μm, more preferably an average particle size of 6
Those having a thickness of 0 μm or less are used. Specifically, powdered ion-exchange resin made by introducing ion-exchange groups into styrene-divinylbenzene copolymer, which has excellent chemical stability and ion-exchange performance, or ion-exchange resin made of acrylic acid-based monomer-divinylbenzene copolymer. It is possible to cite up to crushed ones.

The ion exchange group of the ion exchange fiber and 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 strong 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. Although the weakly basic anion-exchange group obtained by the above is mentioned, a strongly basic anion-exchange group is preferable from the viewpoint of processing performance in the present invention.

As the cation exchange group, an aminocarboxylic acid group such as a sulfonic acid group, a phosphonic acid group, a carboxylic acid group and 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.

As a specific method for producing the ion-exchange fiber in the present invention, a multi-core mixed or composite fiber composed of a polystyrene-based compound and poly-α-olefin is crosslinked to insolubilize the polystyrene part with a formaldehyde source under an acid catalyst, and then A method for producing by introducing an ion-exchange group by a known method, poly-
A method for producing mixed fibers by impregnating α-olefin fibers with styrene-divinylbenzene and introducing an ion-exchange group after copolymerization, ion-exchange groups for polyacrylonitrile / polyamide / polyester fibers by chemical modification or grafting. Can be introduced.

The control of the water content of the ion-exchange fiber depends on the properties of the polymer forming the ion-exchange fiber, and a method suitable for each is used, but in the case of a polystyrene compound, the proportion of the three-dimensional crosslinking degree of the polystyrene part is adjusted. It is possible to give width relatively easily by
In the method of introducing an ion-exchange group by a chemical modification method or a graft method, the ratio of hydrophilic groups or hydrophobic groups is adjusted by changing the graft ratio.

Here, it is important in the present invention that the water content of the ion exchange fiber is in the range of 1.0 to 3.0.

The water content greatly affects the volume and porosity of the ion exchanger in water, and also affects the adsorption rate of impurities.
In general, an ion exchanger having a high water content tends to have a larger impurity adsorption capacity.

When the water content is less than 1.0, the impurity adsorption capacity of the ion exchange fiber itself becomes small and the quality of the treated water deteriorates.
In addition, the volume and porosity of the precoat material in water becomes extremely small, the effect of preventing ion consolidation obtained by mixing the ion-exchange fibers is greatly reduced, and the water pressure increases until the critical pressure is reached. Is very short and the life extension effect is weakened. In addition, the fiber itself becomes rigid, and the characteristics as a fiber with fiexibility are inferior.

On the other hand, when the water content is more than 5.0, the ion-adsorption fiber itself has a large impurity adsorption capacity, but the volume and porosity of the precoat material in water becomes much larger, and it becomes a state like algae in water. Although the effect of preventing consolidation is large, impurities such as ions in the water to be treated are likely to leak, and the quality of the treated water is greatly deteriorated, making it unusable.

Therefore, particularly in applications where importance is attached to water quality such as nuclear condensate treatment, the water content must be in the range of 1.0 to 3.0 because the leakage of impurities must be made extremely small.

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], [R
c, Fa], [Fc, Rc, Fa] [Fc, Fa, Ra] [Fc, Rc, Ra] [Rc, F
a, Ra] [Fc, Rc, Fa, Ra], etc. are preferable considering the improvement of the outlet water quality, and especially [F] for purifying wastewater for nuclear power plants.
c, Rc, Ra] is most preferable. Here, Fc and Fa mean cation and anion exchange fibers, respectively, and Rc and Ra mean powder cation and powder anion exchange resins, respectively.

In the present invention, the ratio of the ion exchange fiber to the total amount of the precoat material is preferably 10 to 60% in terms of dry weight.
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 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 life is reduced in terms of differential pressure. 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 1/10 to 10
Although it is in the range of / 1, 1/2 to 10/1 is particularly preferable for purification of wastewater for nuclear power plants.

The method of use as the precoat material is arbitrary, and for example, a powder cation / anion exchange resin and ion exchange fibers are stirred and mixed in water to form a floc, or a powder cation / anion exchange resin is used.
Anion-exchange resin is stirred and mixed in water to form a floc body, then ion-exchange fibers are mixed and stirred to form a floc body, which is a pre-coating method in one step, a step (multi-stage) pre-coating method, and a body feed pre-coating method. Method, or powder cation-anion exchange resin is stirred and mixed in water to pre-coat as a floc body,
Various combinations such as an over-precoating method of precoating ion-exchange fibers dispersed in water from the above are conceivable. Here, in terms of operation and maintenance,
A method of pre-coating in a single step by a usual method is preferable.

However, in order to further improve the life of the precoat material, it is effective to combine it with the precoat method in consideration of the filtration mechanism such as the step precoat method and the overcoat precoat method.

A dispersant such as a surfactant may be added during stirring and mixing. As the pre-coated support used in the present invention, all the usual pre-coated filters such as a cylindrical type and a leaf-shaped type or a normal-shaped filtration support used for ion exchange filtration can be used, and the system is currently generally used. The method can be applied as it is.

The thickness of the precoat layer is about 2 to 20 mm, preferably about 3 to 10 mm. In the present invention, the passage speed of the aqueous solution to be treated through the precoat layer is about 1 to 20 m / hr, and when the pressure loss reaches about 2 kg / cm ² , backwash by a usual method, and the support is repeatedly used. .

The precoat material of the present invention, which uses the ion-exchange fiber having an appropriate water content and the powder ion-exchange resin, has a much longer life and improved water quality as compared with the conventional precoat material. It has a strong structure in which the thin precoated filter layer is made of powdered ion-exchange resin flocs with ion-exchange fibers at the core and integrated as a whole,
The mixture of the ion-exchange fibers has an appropriate bulkiness, prevents the phenomenon of consolidation during water passage, maintains the porosity necessary for ion exchange or adsorption, and the fiber itself having a large specific surface area is very effective. This is because it has such a good ion exchange function that 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 thereto.

[Example] (Example 1) A multi-core sea-island type composite fiber [sea component polystyrene / island component polyethylene = 50/50 (number of islands 16)] that was spun was cut to a length of 0.3 mm to obtain a cut fiber. The cut fiber 1
Add 1 part by weight to a commercially available crosslinking / sulfonation solution consisting of 7.5 parts by volume of primary sulfuric acid and 0.07 part by weight of paraformaldehyde.
The mixture was reacted at 90 ° 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 3.5 meq / g-Na, fiber diameter approx. 40
The exchange capacity was measured by the following method.

1 g of this cut fiber in 50 ml of 0.1N sodium hydroxide
, Shake for 2 hours, accurately weigh 5 ml, and calculate by neutralization titration.

In addition, the above-mentioned cut fiber converted to Na type was sufficiently immersed in ion-exchanged water, dehydrated with a household centrifugal dehydrator, and the weight (W) was measured, followed by drying in a dryer at 60 ° C for 48 hours. The weight was measured (W ₀ ) and the water content was determined from the following formula.

Water content = (W−W ₀ ) / W ₀ The cation exchange fiber had a water content of 1.6.

Commercially available powder cation exchange resin ["Powdex" -PCH
(Organo Co., Ltd.), having sulfonic acid group, exchange capacity 5.0 meq / g] and commercially available powder anion exchange resin [“Powdex” -PAO (Organo Co.), having trimethylammonium group, exchange capacity 3.2 meq) /
The above ion-exchange fiber was added to the mixture of [g] in a ratio of 30% of the total amount to adjust the cation / anion ratio to 6/1.

Using a column (50 mmΦ) having an acrylic support plate inside, a filter paper was placed on the support plate, and the above-mentioned flock body was deposited on the filter paper to perform precoating. The total amount of flock is 1.96
g (about 1.0 kg / m ² ). From the top, the differential pressure limit value of the precoat material at the nuclear power plant at the flow rate of 8 m / hr of the adjusted simulated liquid containing 5 ppm of amorphous iron (ferric hydroxide, average particle size 3.6 μm) in terms of iron and passing water until 1.75 kg / cm ² being determined to was determined the filtration time (pre-coat life) and the average iron removal rate from the measurement of iron concentration.

The experimental results are shown in Table 1.

(Example 2) Reaction was performed in the same manner as in Example 1 except that the amount of paraformaldehyde was 0.03 parts by weight to obtain a cation exchange fiber having the following properties.

(Water content 2.5, exchange capacity 3.5 meq / g-Na, fiber diameter approx. 40μ
m) The same experiment as in Example 1 was conducted using this cation exchange fiber.

The experimental results are shown in Table 1.

Comparative Example 1 A cation exchange fiber having the following properties was obtained by performing the same reaction as in Example 1 except that the amount of paraformaldehyde was 0.2 part by weight.

(Water content 0.8, exchange capacity 3.5 meq / g-Na, fiber diameter approx. 40μ
m) The same experiment as in Example 1 was conducted using this cation exchange fiber.

The experimental results are shown in Table 1.

(Comparative Example 2) A cation exchange fiber having the following properties was obtained by performing the same reaction as in Example 1 except that the amount of paraformaldehyde was 0.01 part by weight.

(Water content 6.0, exchange capacity 3.5 meq / g-Na, fiber diameter approx. 40μ
m) The same experiment as in Example 1 was conducted using this cation exchange fiber.

The experimental results are shown in Table 1.

(Comparative Example 3) The same experiment as in Example 1 was carried out except that the ion exchange fiber was not used.

The experimental results are shown in Table 1.

From these results, it was found that the mixed system with ion-exchange fibers is very effective in suppressing the increase in differential pressure and improving the water quality of the water to be treated, as compared with the conventional system using only powder ion-exchange resin. However, both of these effects appear in a well-balanced manner when the water content of the ion-exchange fiber is in the range of 1.0 to 5.0.If the water content is too low, the differential pressure rises rapidly and the effect of mixing the ion-exchange fibers Does not appear, the ion adsorption fiber has a poor impurity adsorption capacity, and the water quality deteriorates. Conversely, if the water content is too large, the porosity of the ion exchanger becomes too large, and leakage of impurities occurs and the water quality is significantly deteriorated. I understood it.

In addition, there is a balance within the allowable range of 1.0 to 5.0, and it is necessary to select ion exchange fibers having the optimum water content depending on the place where this treatment method is applied.

[Effects of the Invention] In the method for purifying an aqueous solution according to the present invention, the ion exchange fiber having a water content of 1.0 to 3.0 serves as the core of the powder ion exchange resin to form a floc body, which imparts appropriate porosity and compressive strength. As a result, the service life of the precoat material has been dramatically extended, and the excellent ion exchange performance of the fiber having a large surface area has made it possible to improve the quality of treated water. This is a very simple method in which the ordinary precoat method can be used as it is, and is very effective.

INDUSTRIAL APPLICABILITY 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 a worker who is concerned at a nuclear power plant can be greatly reduced.

The liquid to be treated in which the present invention is used is not limited and is applied to all those using a precoat filter,
It is especially effective for wastewater from nuclear power plants and thermal power plants.

Wastewater from nuclear power plants and thermal power plants
Fuel pool water, demineralizer backwash wastewater, steam generation blow water, wet water separator drain water, cavity water, depression pool water, core water, etc. Indicates.

 ─────────────────────────────────────────────────── --Continued from the front page Judgment panel for referees Chief referee Yasuo Yoshimura Referee Mitsuru Yamada Referee Kenji Hara (56) References JP 55-67384 (JP, A) JP 62-11593 (JP, A) JP-A 63-44988 (JP, A) JP-A 1-159096 (JP, A)

Claims (1)

[Claims] 1. A method for purifying an aqueous solution by a precoat filter, wherein ion exchange fibers comprising a powder ion exchange resin and an ion exchange polymer and a reinforcing polymer are used as a precoat material, and the water content of the ion exchange fibers is 1.0 to. A method for purifying an aqueous solution, which is 3.0.