JPH0330891A - Purification of aqueous solution - Google Patents

Abstract

PURPOSE:To extend the filtering life of precoat to a large extent and to enhance the quality of treated water by using a powdery ion exchange resin and an ion exchange fiber as a precoat material and performing the coating operation of an element with the precoat material in parts before and during the treatment of raw water. CONSTITUTION:A powdery ion exchange resin and an ion exchange fiber are used as a precoat material and the precoating operation of an element with the precoat material is performed in parts before and during the treatment of raw water. The filter material precoated before the treatment of raw water collects impurities by internal filtration and, at the point of time when the internal filtration changes to surface filtration as impurities become a cake form with the advance of filtration, the filter material is further precoated with the new precoat material to perform internal filtration by a new precoat layer and, therefore, an internal filtration time can be effectively secured by the same amount of the precoat layer. Further, the life of the precoat material is extended by the mixing with the ion exchange fiber and the quality of treated water can be enhanced.

Description

[Detailed Description of the Invention] [Industrial Application Field] 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 in particular uses a precoat filter. This relates to a method for purifying aqueous solutions.

[Prior Art] Conventionally, in precoat type filters for purifying water and wastewater in nuclear power plants, thermal power plants, etc., powdered ion exchange resin has been used as a precoat material.

Precoat filtration is a general term for a method in which a filtration layer with a certain thickness is formed using a precoat material on some kind of support, and the water to be treated passes through that layer to remove impurities contained therein. There is a method in which a powdered ion exchange resin is precoated on a support element by hydraulic pressure, and the water to be treated is passed through the precoat to purify it, and this device is called a precoat filter.

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, and the differential pressure is rate-limiting at the time of backwashing.

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

Therefore, for the purpose of reducing waste, it has become necessary to extend the period from precoating to backwashing (water sampling life with one precoat material) as long as possible.This is simply due to the differential pressure of the precoat material. It is not enough just to prevent the water from rising and extend the life of the sampled water; it is meaningless unless the quality of the treated water is equal to or better than that of existing materials.

If it were possible to improve the quality of treated water, it would also be highly effective in significantly reducing radiation exposure for nuclear power plant workers.

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).

In addition, in order to improve the filtration process, a method of precoating powdered ion exchange resin in stages during the treatment of the raw solution (hereinafter referred to as step precoating) was devised as a method to extend the life of the filter medium. (Tokuko Sho 63-29
571). This is a method designed to extend the internal filtration process time of the filter medium as much as possible.

When the precoat layer filters impurities, internal filtration is first performed in which the impurities are diffused and adsorbed inside the precoat layer, and then the impurities are captured by the impurities formed on the layer surface and the densified surface cake formed by the precoat material. It is known that the filtration process progresses to the surface filtration of the precoat layer. Here, it is also known that the filtration pressure of the precoat layer is gentle during internal filtration, but increases sharply when transitioning to surface filtration.

[Problems to be Solved by the Invention] However, the method of mixing ion exchange fibers is difficult because the precoat layer made of ion exchanger has an appropriate porosity and does not become compacted when water passes through it, and the step precoat does not allow internal Although this method was effective in extending the life of the precoat material compared to conventional methods by extending the filtration process time, it is difficult to say that this effect has yet achieved the goal from the perspective of significantly reducing waste.

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

[Means to solve the problem] That is, the present invention has the following configuration.

In the precoat filtration method, which purifies impurities in raw water by precoating a filter material onto an element, powdered ion exchange resin and ion exchange fiber are used as the precoat material, and the operation of coating the element with the precoat material is performed before raw water treatment. An aqueous solution purification method characterized by performing the treatment in parts during raw water treatment.

The present invention will be explained in detail below.

The ion-exchange fiber of the present invention is not particularly limited, and any ion-exchange polymer may be used as long as the ion-exchange polymer has a fiber form.In particular, it has the advantage of effectively suppressing the compaction of the pre-coat layer in order to extend the life of the pre-coat material. Preferably, the fiber is made of an ion exchange polymer and a reinforcing polymer.

The mixing mode of the ion-exchange polymer and the reinforcing polymer is not particularly limited, but for example, core-sheath type fibers, multi-core mixed fibers, and multi-core composite fibers in which the ion exchange polymer is the main component of the sheath component and the reinforcing polymer is the core component. is 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.

Ion exchange polymers include, but are not limited to, polystyrene, polyacrylic, and polyamide.

Examples include polymers in which ion exchange groups are introduced into polyester-based, polyvinyl alcohol-based, polyphenol-based, poly-α-olefin-based compounds, and the like. 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.

In addition, examples of the reinforcing polymer include poly-α-olefin, polyamide, polyester, polyacrylic, etc., but the reinforcing polymer is not limited thereto. Among these, poly-α-olefin is preferred because it has excellent chemical resistance for producing ion-exchange fibers. Examples of the poly-α-olefin include, but are not limited to, polyethylene, polypropylene, poly-3-methylbutene-1, poly-4-methylpentene-1, and the like.

The diameter of such ion exchange fibers is preferably 10 to 100 μm from the viewpoint of having a high specific surface area and preventing compaction of the precoat layer. More preferably 20-70μm1, especially 30-70μm1
5'0 μm (dry state) is most preferred.

In addition, the fiber length is set to 0.0 mm for the purpose of maintaining an appropriate porosity of the precoat layer. 1 to IM is preferred. More preferably,
0.15-0.6 mm, especially 0.2-0.4 mm is most preferred.

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

The powdered 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, 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-based monomer divinylbenzene copolymers, down to powder. It can be crushed.

The ion exchange group of the ion exchange fiber and powdered 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, and morpholine can be used. Examples include weakly basic anion exchange groups obtained by the following, but strongly basic anion exchange groups are preferable from the viewpoint of treatment performance in the present invention.

As the cation exchange group, a sulfonic acid group, a phosphonic acid group, a carboxylic acid group, an aminocarboxylic acid group such as an iminodiacetic acid group, etc. are preferably used, and a sulfonic acid group is more preferable in terms of treatment performance in the present invention.

A specific method for producing ion exchange fibers is to crosslink and insolubilize the polystyrene portion of a multicore mixed or composite fiber made of a polystyrene compound and poly-α-olefin with a formaldehyde source under an acid catalyst, and then to insolubilize the polystyrene portion by a known method. A method for producing mixed fibers by impregnating poly-α-olefin fibers with styrene-divinylbenzene and introducing ion exchange groups after copolymerization, polyacrylonitrile/polyamide/polyester Examples include, but are not limited to, methods of manufacturing core-sheath type fibers by introducing ion exchange groups into the outer layer of 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, R
ako, [Rc, Fa], [Fc
, Rc.

Fa] [Fc, Fa, Ra] [Fc, Re, R
ako [Rc, Fa, Ra] [F
c, Rc, Fa.

[Fc, Rc, Ra] etc. are preferable in consideration of improving the quality of the outlet water, and especially for purifying wastewater of nuclear power plants, [Fc, Rc, Ra] etc.
is most preferred. Here, Fc and Fa mean cation and anion exchange fibers, respectively, and Rc and Ra mean powder cation and powder anion exchange resin, 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. More preferably 15 to 50%, still more preferably 20%
~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, but 1/2 to 10/1 is particularly suitable for purifying wastewater from nuclear power plants. preferable.

Here, a major feature of the present invention is that the operation of precoating the element with the precoat material is performed separately before and during raw water treatment. This is a method in which the filter material pre-coated before raw water treatment captures impurities through internal filtration, and then a new pre-coat material is pre-coated on top of it when the impurities change to surface filtration as the impurities become cake-like. Since this method performs internal filtration, the same amount of precoat layer can provide more effective internal filtration time. The above material can be used as a pre-coat material in any manner. For example, stirring and mixing powdered cation/anion exchange resin and ion exchange fiber in water to form a flock; stirring and mixing powdered cation/anion exchange resin in water to form a flock After that, ion exchange fibers are mixed and stirred to form a floc, or powdered cation exchange resin, anion exchange resin, and ion exchange fiber are stirred and mixed in water to form a floc, and then ion exchange fibers are mixed and stirred and mixed. It can be adjusted using the usual method such as making it into a flocked body, and then step-precoated.

Further, a dispersant such as a surfactant may be added during stirring and mixing.

As the precoat support used in the present invention, all filtration supports in the usual shapes used for normal precoat filters, ion exchange filtration, etc., such as a cylindrical nine-lobed type, can be used.

Further, the thickness of the precoat layer is preferably 1.
5-15 mm, more preferably 2-10 mm.

The second stage is preferably 0.5 to 10 mm, more preferably 1 to 5 mm. This is because if the thickness of the first stage precoat is too thin, the initial impurity capture rate will decrease and the quality of the treated water will tend to deteriorate; if it is too thick, the second stage precoat thickness will decrease and the internal filtration period will be shortened. This is because the effect of pre-coating may not be effective.

In the present invention, the timing to start the second stage precoating is 1
After precoating the stage, the water to be treated is passed through and the water flow differential pressure is 0.
It is preferable that it is about 0.01 to 0.4 kg/cti, more preferably 0.05 to 0.05 kg/cti. 2kg/a
At this point, the water flow is temporarily stopped and the second stage of precoating is performed.

Also, the number of times of step precoating is not fixed as two steps, and of course it may be performed in several steps, but the purpose is to minimize the amount of waste precoat material, extend the life of the precoat, and improve the quality of the treated water. If the layers are stacked thinly in multiple layers, a large amount of precoat material will be used or there is a risk of deterioration of water quality, so 2 to 3 layers is preferable.

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 water flow pressure loss of the precoat layer reaches about 2 kg/ad, it is backwashed by a normal method and the support is removed. The body is used repeatedly.

Compared to the conventional pre-coat filtration method, the present invention has made it possible to significantly extend the service life and improve water quality.

Firstly, it has a durable structure in which the thin pre-coated filtration layer is formed from a flock of powdered ion exchange resin with ion exchange fibers as the core, and is integrated as a whole, and ion exchange fibers are mixed in. Pre-coated fibers have an appropriate bulk, prevent compaction during water passage, maintain the porosity necessary for ion exchange or adsorption, and have a large specific surface area.The fiber itself has a very effective ion exchange function. Impurities in the aqueous solution to be treated (colloids such as crud, ions, etc.) can be taken in between the grains of the entire layer without waste.Secondly, step precoating is performed and internal filtration is performed over two layers to extend the internal filtration period. The two effects of suppressing the increase in the differential pressure through the liquid and making effective use of the capacity of the precoating material are achieved without compromising each other, and by combining the ion exchange fiber mixing method and the step precoating method, the resin It was found that step precoating produced two new effects of compaction prevention, which were not observed at all with step precoating. This is an effect resulting from the difference in material distribution of the amount of precoat material when pressure is applied.

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

[Example] (Example) Spun multicore sea-island composite fiber [sea component polystyrene/island component polyethylene = 50150 (number of islands 16)] with length 0
．． Cut eye bars were obtained by cutting in three steps. 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 1-absorbed sulfuric acid and 0.1 part by weight of paraformaldehyde, and reacted at 90°C for 4 hours.
After reacting at ℃ for 3 hours, it was washed with water. Next, a cation exchange fiber having sulfonic acid groups was obtained by treating with an alkali and then activating with hydrochloric acid. (Exchange capacity: 3.5 milliequivalents/g Na + fiber diameter of about 40 μm) The exchange capacity was measured by the following method.

1 g of this cut fiber was added to 50 ml of sodium hydroxide at 0.0000000000000000000000000000000000000000000000000 IN, and 1 g of this cut fiber was added to 50 ml of sodium hydroxide and shaken for 2 hours.

Commercially available powder cation exchange resin [“Powdex”-PC
I (Organo Co., Ltd.), has 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
The ion exchange fibers were added to a mixture of milliequivalents/g at a ratio of 30% of the total amount, and the cation/anion ratio was adjusted to 6/1 to prepare a floc.

Using a column (50-φ) equipped with an acrylic support plate inside, a filter paper was placed on the support plate, and 1.37 g (approximately 70% of the total amount) of the above floc was deposited on it and precoated. . The thickness of the cake at that time was 3.5 mm.

From the top, 5 ppm of amorphous iron (ferric hydroxide,
A simulated liquid containing particles with an average particle size of 3.6 μm was applied at 8 m/h.
Water was passed through the tube at a flow rate of r, and the filtration time, iron concentration, and water flow differential pressure were measured. When the water flow differential pressure rises to about 0.1 kg/-, the water flow of the liquid to be treated is temporarily stopped, and the remaining floc body 0.6
g (approximately 30% of the total amount) was pre-coated from above. The thickness of the second tier cake was 1.7 mm. Add the above simulated liquid to 8
m / hr flow rate, about 1,8 kg / hr, which is determined as the differential pressure limit for precoated materials in nuclear power plants.
Water was passed through the tube again until c&, and the iron capture rate was calculated by observing changes in outlet water quality from measurements of filtration time (precoat life) and iron concentration.

After the experiment was completed, the cake used was taken out in its original form and the thickness of the cake was measured to examine the degree of compaction.

The results are shown in Table 1.

(Comparative Example 1) A flock cake was made in the same manner as in Example 1 except that ion exchange fibers were not mixed, and an experiment was conducted in exactly the same manner as in Example 1.

The thickness of the first stage pre-coat cake before stock solution treatment is 3゜11I
The step height for IIN+ was 1.5 mm.

The experimental results are shown in Table 1.

(Comparative Example 2) The number of precoating steps was set to 1, and the flock body weighed 1°96g (
Approximately 1. 0kg/rr? An experiment was carried out in exactly the same manner as in Example 1, except that the usual precoating method of precoating 20% of the sample was used.

The thickness of the precoat cake before stock solution treatment is 5. It was 2 mm.

The experimental results are shown in Table 1.

(Comparative Example 3) Not mixing ion-exchange fibers and precoating the number of times by 1
1.96g of flock body (approximately 1゜Okg/rr
An experiment was carried out in exactly the same manner as in Example 1, except that a normal precoating method was used in which f) was precoated twice.

The thickness of the precoat cake before the stock solution treatment was 4.8M.

The experimental results are shown in Table 1.

These results show that mixing ion-exchange fibers extends lifespan and improves water quality, and using the step precoat method extends lifespan by extending the internal filtration period, but using both together does not impair these effects. Furthermore, the step precoating method, which was completely unseen with resin-only systems, improved the compaction prevention effect, which was unprecedented in terms of extending the life of the precoating material of the present invention and improving water quality. It turned out to be an effective method.

[Effects of the Invention] The aqueous solution purification method according to the present invention extends the life of the precoat material by imparting appropriate porosity and compressive strength to the floc by mixing ion-exchange fibers, and improves the quality of the fibers with a large surface area. The ion exchange performance makes it possible to improve the quality of the treated water, and step pre-coating extends the internal filtration period of the floc, suppressing the increase in water flow differential pressure and making effective use of the ion exchange performance of the entire floc. These two effects dramatically extended the life of the precoat material and also made it possible to improve water quality.

Moreover, the present invention exhibits an effect of preventing compaction due to the step precoating method, which was not observed at all with resin-only systems.
It has become possible to extend the lifespan further than expected from the known effects mentioned above.

As a result, the waste volume of variously used precoat materials for water treatment can be reduced, and the amount of radiation exposure of workers, which is a concern especially in nuclear power plants, can be significantly reduced.

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

Wastewater from nuclear power plants and thermal power plants refers to circulating condensate and
Examples include fuel pool water, desalination equipment backwash wastewater, steam generation blow water, water loss separator drain water, cavity water, suppression pool water, and core water, among which it is particularly effective in purifying nuclear condensate. .

Claims (1)

[Claims] In the precoat filtration method, which purifies impurities in raw water by precoating a filter material onto an element, powdered ion exchange resin and ion exchange fiber are used as the precoat material, and the operation of coating the element with the precoat material is performed before raw water treatment. An aqueous solution purification method characterized by performing the treatment in parts during raw water treatment.