JPH04227809A - Method for purifying aqueous solution - Google Patents

Abstract

PURPOSE:To improve the quality of treated water and to prolong the service life of a precoat. CONSTITUTION:An aq. soln. is purified by a precoated filter. The precoat is formed with a powdery ion-exchange resin A and an ion-exchange fiber B consisting of an ion-exchange polymer and a reinforcing polymer, and at least the ion-exchange fiber B is precoated by the body feed method.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a method for removing impurities contained in service water and wastewater in nuclear power plants, thermal power plants, pharmaceutical companies, etc., and particularly relates to a method for purifying aqueous solutions using a precoat filter. It is.

0002

BACKGROUND OF THE INVENTION Conventionally, powdered ion exchange resin has been used as a precoat material in precoat type filters for purifying water and wastewater in nuclear power plants, thermal power plants, and the like. Precoat filtration is a process in which a filtration layer with a certain thickness is formed using a precoat material on some kind of support.
It is a general term for a method in which impurities contained in the water to be treated are removed by passing the water through the layer. Recently, there is a method in which a powdered ion exchange resin is precoated on a support element using hydraulic pressure, and the water to be treated is passed through that layer to purify it.
This device is called a precoat filter.

[0003] This precoat material is backwashed and replaced with a new precoat material when the differential pressure during water flow reaches a certain value. However, in many cases, the specified differential pressure is reached before the ion exchange capacity of the precoat material is effectively used up.
The time of backwashing was controlled by differential pressure.

[0004] Particularly in nuclear power plants, waste precoat materials that have been backwashed and recovered are all subject to storage and storage because they contain radioactive materials, and the ever-increasing number of such treatments has become a new social problem.

[0005] Therefore, for the purpose of reducing waste, it has become necessary to lengthen the period from precoating to backwashing (the life span of water sampling with one precoating material) as long as possible. This is not just a matter of preventing the differential pressure rise of the precoat material and extending the water sampling life; it is meaningless unless the quality of the treated water is equal to or better than that of existing materials.

[0006] If it were possible to improve the quality of treated water, it would be extremely effective in significantly reducing the radiation exposure of nuclear power plant workers.

[0007] As a method to deal with this, it was considered to improve the precoat material, and the use of ion exchange fibers as the precoat material was devised (Japanese Patent Laid-Open No. 55-67384).
.

[0008]

[Problems to be Solved by the Invention] However, these ion exchange fibers are only effective at preventing the precoat material from physically cracking, and are not capable of achieving the above object.

[0009] In order to practically extend the life of the precoat material, it is required that the precoat layer composed of an ion exchanger has an appropriate porosity and that it is not compacted when water is passed through it. Furthermore, in order to improve water quality, it is important that the ion exchanger constituting the precoat layer has a large specific surface area and exchange capacity.

In precoat filtration, the water to be treated is purified by the internal filtration mechanism of the precoat layer at the beginning of water passage, and as the filtration progresses, it is transferred to the surface filtration mechanism of the precoat material. At this time, it is known that during the internal filtration period, there is almost no increase in the water flow differential pressure, but as soon as the transition to surface filtration occurs, a rapid increase in the differential pressure is observed. For extension, it is necessary to extend the internal filtration period.

Moreover, in the conventional method of precoating the entire element with the precoat material and then passing the treated water through it for treatment, only the part of the precoat material that is in contact with the water to be treated is used, and the precoat material goes inside the precoat layer. Accordingly, its ion exchange and adsorption capacity was discarded without being used, resulting in very low efficiency.

An object of the present invention is to provide an aqueous solution purification method that eliminates the drawbacks of the prior art, extends the filtration life of the precoat, and improves the quality of treated water compared to conventional methods. It is.

[0013]

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

[0014] In the method of purifying an aqueous solution using a precoat filter, the precoat material is composed of a powdered ion exchange resin (a) and ion exchange fibers (b) made of an ion exchange polymer and a reinforcing polymer, and at least the ion exchange A method for purifying an aqueous solution, characterized in that fibers (b) are precoated by a body feed method.

The present invention will be explained in detail below.

The ion exchange fiber (b) used in the present invention is
The fiber is made of an ion exchange polymer and a reinforcing polymer, and the reinforcing polymer maintains its strength and can effectively prevent the precoat layer from becoming compacted.

The manner in which the ion exchange polymer and the reinforcing polymer are mixed is not particularly limited, but for example, core-sheath type fibers in which the ion exchange polymer is the main component of the sheath component and the reinforcing polymer is the core component,
Multicore mixed and multicore composite fibers are preferably used. In particular, multifilamentary composite fibers are preferred because they have sufficient mechanical strength, are effective in preventing compaction, and have a large specific surface area as an ion exchanger.

The proportion of the reinforcing polymer in the ion exchange fiber (b) is preferably 10 to 10, because if it is too small, the mechanical strength will be weakened, and if it is too large, the ion exchange capacity and adsorption amount will be reduced. 70%, more preferably in the range of 20-50%.

Ion exchange polymers are not particularly limited, but include polymers with ion exchange groups introduced into polystyrene, polyacrylic, polyamide, polyester, polyvinyl alcohol, polyphenol, poly-α-olefin compounds, etc. can be mentioned. In particular, a polymer obtained by introducing an ion exchange group into a crosslinked and insolubilized polystyrene 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 poly-α-olefin, polyamide, polyester, polyacrylic, etc., but are not limited to these. Among these, poly-α-olefin is preferred because it has excellent chemical resistance for producing ion-exchange fibers. Poly-α-olefins include polyethylene, polypropylene, poly-3-methylbutene-1, poly-4-methylpentene-
Examples include, but are not limited to, 1st grade.

[0021] The diameter of such ion-exchange fibers is 15 to 15, from the viewpoint of having a high specific surface area and preventing compaction of the precoat layer.
100 μm is preferred. More preferably 20 to 70 μm
, especially 30 to 50 μm (dry state) is most preferred.

Further, 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.

[0023] The cross-sectional shape of this fiber may be circular or various other shapes.

Powdered ion exchange resin (a) in the present invention
The particles preferably have a particle size of 1 to 250 μm, and more preferably have an average particle size of 60 μm or less. Specifically, we use ion exchange resins made by introducing ion exchange groups into styrene-divinylbenzene copolymers, which have excellent chemical stability and ion-exchange performance, or ion-exchange resins made from acrylic acid monomer-divinylbenzene copolymers, down to powder. It can be crushed.

The ion exchange group of the ion exchange fiber (b) and powdered ion exchange resin (a) in the present invention means an anion exchange group or a cation exchange group.

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

[0027] As the cation exchange group, sulfonic acid group,
Aminocarboxylic acid groups such as a phosphonic acid group, a carboxylic acid group, and an iminodiacetic acid group are preferably used, but a sulfonic acid group is more preferred in terms of treatment performance in the present invention.

[0028] As a specific method for producing the ion exchange fiber of the present invention, a multicore mixed or composite fiber made of a polystyrene compound and a poly-α-olefin is crosslinked and insolubilized using a formaldehyde source under an acid catalyst. Next, a method of manufacturing by introducing an ion exchange group by a known method, a method of manufacturing a mixed fiber by impregnating poly-α-olefin fiber with styrene-divinylbenzene and introducing an ion exchange group after copolymerization, Examples include a method of manufacturing core-sheath type fibers by introducing ion exchange groups into the outer layer of polyamide or polyester fibers by chemical modification, grafting, or the like.

Here, the combination of ion exchange fiber and powdered ion exchange resin as the precoat material in the present invention is [
Fc, Ra], [Rc, Fa], [Fc, Rc, Fa]
, [Fc, Fa, Ra], [Fc, Rc, Ra], [R
c, Fa, Ra] [Fc, Rc, Fa, Ra] and the like are preferable in consideration of improving the quality of the outlet water, and particularly [Fc, Rc, Ra] is most preferable for purifying wastewater from nuclear power plants. Here, Fc and Fa mean cation and anion exchange fibers, respectively, and Rc and Ra mean powder cation and powder anion exchange resin, respectively.

[0030] In the present invention, the ratio of ion exchange fiber to the total amount of precoat material is 10 to 6 in terms of dry weight.
0% is preferred. More preferably 15 to 50%, still more preferably 20 to 40%. This means that if the fiber content is too low, the precoat layer will have a moderate porosity, compaction prevention effect, and high specific surface area. This is because the quality of the treated water will be poor, although the water will increase. 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 purification of wastewater from nuclear power plants, the ratio is preferably from 1/2 to 10/1, particularly preferably from 1/1 to 10/1.

[0031] What is important in the present invention is to use the body feed method for precoating. In the body feed method, for example, first, a powdered cation exchange resin and a powdered anion exchange resin are stirred and mixed in water to form a flock, or ion exchange fibers are mixed therein to form a three-part flock, which is thinly precoated. This refers to a method in which a slurry of ion-exchange fiber alone or a powdered ion-exchange resin mixed therein and the water to be treated are simultaneously passed continuously and/or intermittently. Considering the practicality of operation, it is preferable that the ion exchange fiber alone be passed through at the same time as the water to be treated. In this method, the impurities in the water to be treated come into contact with the pre-coat material, which has a high degree of freedom, and are adsorbed before forming the pre-coat layer, so the internal filtration period can be maintained for an extremely long time, and the rise in differential pressure can be effectively controlled. can be prevented. In addition, since the cladding is incorporated into the entire volume of the precoat layer, the adsorption capacity of the precoat material is 100%.
It can be used effectively without waste, and is very effective in improving water quality.

Further, a dispersant such as a surfactant may be added during stirring and mixing of the precoat material.

[0033] As the precoat support used in the present invention, all the usual shapes of filtration supports used in ordinary precoat filters, ion exchange filtration, etc., such as cylindrical and leaf-shaped, can be used. can be applied as is by simply incorporating a body feed line into the currently commonly used equipment.

[0034] Here, the total 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 to the precoat layer is about 1 to 20 m/hr, and when the pressure loss reaches about 1.5 to 2 kg/cm2, the support is backwashed by a normal method. Use repeatedly.

[0035] The precoat material using the ion exchange fiber and powdered ion exchange resin of the present invention has a significantly longer service life and improved water quality compared to conventional precoat materials. It has a durable structure in which a thin pre-coated filtration layer is integrated with ion exchange fibers and powdered ion exchange resin. The effect of the polymer prevents compaction during water passage, maintains the porosity necessary for ion exchange or adsorption, and the fibers themselves, which have a large specific surface area, have a very effective ion exchange function, so the intergranularity of the entire precoat layer is maintained. Eliminate impurities (colloids such as crud, ions, etc.) in the water to be treated without wasting any waste.
This is because it is possible to incorporate Furthermore, by using an innovative pre-coating method called the body feed method, we have extended the internal filtration period and effectively utilized the ion exchange and adsorption capacity of the pre-coated material, making it possible to further extend the service life and improve water quality. .

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

[0037]

[Example] The multicore sea-island type composite fiber [sea component polystyrene/island component polyethylene = 50/50 (number of islands 16)] was made into yarn with a length of 0.
．． A cut fiber was obtained by cutting to 3 mm. 1 part by weight of the cut fiber was added to a crosslinking/sulfonation solution consisting of 7.5 parts by volume of commercially available primary sulfuric acid and 0.1 part by weight of paraformaldehyde, and reacted at 90°C for 4 hours, and then
After reacting at 0°C for 3 hours, it was washed with water. Next, a cation exchange fiber having a sulfonic acid group was obtained by treating with alkali and activating with hydrochloric acid (exchange capacity: 3.5 meq/g-Na, fiber diameter: approximately 40 μm).

The exchange capacity was measured by the following method.

After putting 1 g of this cut fiber in 50 ml of 0.1N sodium hydroxide and shaking for 2 hours, 5 ml of the solution was accurately weighed and calculated by neutralization titration.

A commercially available powdered cation exchange resin ["Powdex"-PCH (Organo Co., Ltd.), having a sulfonic acid group, exchange capacity 5.0 meq/g] and a commercially available powdered anion exchange resin ["Powdex"-PAO] (Organo Co., Ltd.), has a trimethylammonium group, exchange capacity 3.2 meq/g], cation/anion ratio 3
/1 and adjusted to 1.37 g, and stirred and mixed in pure water to form a floc. A column (50 mmφ) equipped with an acrylic support plate inside was used, filter paper was placed on the support plate, and the above floc was deposited thereon for precoating. Next, one was prepared by dispersing the above cation exchange fiber in pure water, and the other was prepared using a prepared simulated material containing 5 ppm of amorphous iron (ferric hydroxide, average particle size 3.6 μm) in terms of iron. Two tanks of liquid were prepared. A line was created so that each column could be sent from this tank to the column using a separate pump. Amorphous iron is fed into the column at a flow rate of 8 m/hr, and at the same time, water is passed through with another pump so that the concentration of cation exchange fiber in the water to be treated is about 10 ppm, and the column is treated with body feed. Water was passed until the water pressure difference reached 1.75 kg/cm2, which was determined as the differential pressure limit value of the precoat material, and the average iron removal rate was determined from the measurement of the filtration time (precoat life) and iron concentration. The results are shown in Table 1.

Comparative Example 1 Powdered ion exchange resin (1.37 g) used in the example prepared in advance to have a cation/anion ratio of 3/1
) and ion exchange fiber (0.68
30% of the total amount) in pure water with stirring to form a flock body (2
．． 05g) and precoated onto the column used in the example. After that, water was passed through the simulated solution used in the example until the differential pressure reached 1.75 kg/cm2, which was determined as the differential pressure limit value of the precoat material, and the filtration time (precoat life) and iron concentration were measured. The average iron removal rate was determined.

The results are shown in Table 1.

[0043] From these results, it was found that by using the body feed method, the life of the precoat material could be significantly extended without any deterioration in the quality of the treated water.

Comparative Example 2 Cation exchange fibers were obtained in the same manner as in Example except that polystyrene fibers without reinforcing polyethylene were used (exchange capacity 5.0 meq/g-Na, fiber diameter approximately 4
0μm).

Although this fiber was extremely brittle and difficult to use, it was used as it was in the experiment, and the same experiment as in the example was conducted. The results are shown in Table 1.

[0046] From these results, it was found that the effect of mixing the ion exchange fibers with the reinforcing material was very effective in suppressing the increase in differential pressure in the precoat layer.

Comparative Example 3 An experiment was carried out in exactly the same manner as in the example except that a powdered cation exchanger was used as the cation exchanger that was passed through at the same time as the water to be treated, and no ion exchange fibers were used. The results are shown in Table 1.

From the results so far, it has been found that the combination of the body feed method and the use of ion exchange fibers as a precoat material is even more effective, and that they do not interfere with each other's effects in any way.

[0049]

[Table 1]

[0050]

[Effects of the Invention] The aqueous solution purification method according to the present invention improves the lifespan of pleated materials by combining ion exchange fibers with a reinforcing polymer and powdered ion exchange resin to impart appropriate porosity and compressive strength. In addition, the excellent ion exchange performance of the fibers with a large surface area also made it possible to improve the quality of treated water. In addition, by using the body feed method as the precoat method, it became possible to extend the internal filtration period and effectively utilize the ion exchange and adsorption capacity of the precoat material, making it even more effective.

[0051] According to the present invention, the waste volume of variously used precoat materials for water treatment can be reduced, and radiation exposure of workers, which is a concern especially in nuclear power plants, can be greatly reduced.

The water to be treated to which the present invention is applied is not limited to any type, and is applicable to all types of water that use a precoat filter, but it is particularly effective for wastewater from nuclear power plants and thermal power plants. be.

[0053] What is wastewater from nuclear power plants and thermal power plants?
These include circulation system condensate, fuel pool water, desalination equipment backwash wastewater, steam generation blow water, wet water separator drain water, cavity water, subreduction pool water, and core water, among which nuclear condensate is particularly It is highly effective in purifying.

Claims (1)

[Claims] Claim 1. A method for purifying an aqueous solution using a pre-coating filter, wherein the pre-coating material comprises a powdered ion exchange resin (a) and an ion exchange fiber (b) made of an ion exchange polymer and a reinforcing polymer, and at least A method for purifying an aqueous solution, characterized in that ion exchange fiber (b) is precoated by a body feed method.