WO2020255680A1

WO2020255680A1 - Ion-exchange fiber, and ion-exchange filter containing same

Info

Publication number: WO2020255680A1
Application number: PCT/JP2020/021509
Authority: WO
Inventors: 丹後佑斗
Original assignee: 日本エクスラン工業株式会社
Priority date: 2019-06-20
Filing date: 2020-06-01
Publication date: 2020-12-24
Also published as: JP7441429B2; CN114007743A; CN114007743B; JPWO2020255680A1

Abstract

Strongly acidic cation-exchange resins, chelate resins, weakly acidic cation-exchange resins, etc. have conventionally been used for removing metal ions present in aqueous solutions. However, there are problems in that strongly acidic cation-exchange resins require large amounts of acids for regeneration and have low selectivity for adsorbed ions, chelate resins have good selectivity but low ion-exchange capacity, and weakly acidic cation-exchange resins have relatively good selectivity but suffer from high breakthrough of heavy metal ions under high flow rates. The purpose of the present invention is to provide an ion exchanger having good selectivity for heavy metals, high ion-exchange capacity, and suppressed breakthrough.　The present invention pertains to an ion-exchange fiber characterized by having an amount of carboxyl groups of 7.0-11.0 mmol/g, a degree of water swelling of 0.5-1.5 g/g, a fineness of 1.0-3.0 dtex, and a breakthrough exchange capacity ratio of at least 40%.

Description

Ion exchange fibers and ion exchange filters containing the fibers

The present invention relates to an ion exchange fiber and an ion exchange filter containing the fiber, and more specifically, to an ion exchange filter made of a non-woven fabric or a papermaking sheet.

As conventional ion exchange fibers having cation exchange properties, strongly acidic cation exchange resins, chelate resins, weakly acidic cation exchange resins and the like have been known. These have been used for removing metal ions present in an aqueous solution.

The strongly acidic cation exchange resins listed above are known to mainly have a sulfonic acid group. Since the ion exchange resin is relatively inexpensive and has a neutral salt resolution, it is used for purifying water to remove Na ions and the like in water (for example, Patent Document 1).

Chelate resins are known to have various functional groups, and in particular, those having iminodiacetic acid groups and polyamine groups are known. These functional groups are used for recovering valuable metals such as Cu and Ni existing in water (for example, Patent Document 2).

Further, it is known that the weakly acidic cation exchange resin mainly has a carboxyl group. The ion exchange resin is used for softening applications such as removing Ca and Mg ions in water by utilizing its features of ease of regeneration and high ion exchange capacity (for example, Patent Document 3).

Japanese Unexamined Patent Publication No. 10-0288879 Japanese Unexamined Patent Publication No. 2016-22148 Japanese Unexamined Patent Publication No. 2016-005835

However, focusing on the use of removing heavy metals such as Cu, Ni, and Pb, the strongly acidic cation exchange resin having a sulfonic acid group has a strong bond with the metal ion, and it is necessary to use a large amount of acid for regeneration. was there. In addition, there is a difficulty in the selectivity of adsorbed ions, and there is a drawback that Cu, Ni, Pb and the like can hardly be adsorbed in an aqueous solution containing a hardness component such as Ca.

On the other hand, the chelate resin has good selectivity for heavy metals and can be said to be an ion exchange resin specialized for recovery and removal of heavy metals. However, the ion exchange capacity is small and a large amount of chelate is required to obtain an effect in actual use. I had to use resin.

Further, the weakly acidic cation exchange resin having a carboxyl group has better selectivity than the strongly acidic cation exchange resin having a sulfonic acid group, and can adsorb trace heavy metal ions in hard water, but has a particle shape. Since there is a limit to miniaturization in order to secure the flow path, the specific surface area cannot be increased. For this reason, the flow of heavy metal ions increases under high flow velocity, and water treatment at low flow velocity is unavoidable.

The present invention has been devised in view of the current state of the prior art, and an object of the present invention is to provide an ion exchanger having good selectivity for heavy metals, a high ion exchange capacity, and suppressed flow through. Is to provide.

As a result of sincere studies to achieve the above-mentioned object, the present inventors used acrylic fiber having a fine fineness as a starting material and formed a high-density carboxyl group by hydrolysis to form a high-density carboxyl group against heavy metals. We have found that an ion exchange fiber having good selectivity, a high ion exchange capacity, and suppressed flow through can be obtained, and have reached the present invention.

That is, the present invention is achieved by the following means.
(1) The amount of carboxyl groups is 7.0 to 11.0 mmol / g, the degree of water swelling is 0.5 to 1.5 g / g, and the fineness is 1.0 to 3.0 dtex. An ion exchange fiber having a once-through exchange capacity ratio of 40% or more as measured by the above.
(Method) An ion exchange filter made of a mixture of 30% by mass of ion exchange fibers and 70% by mass of heat-sealed fibers and having a density of 0.33 g / cm ³ was wound and then heat-bonded to prepare an ion exchange filter. The filter is attached to the filter housing, and an aqueous solution having a Cu (copper) concentration of 3 ppm and a Ca (calcium) concentration of 12 ppm and adjusted to pH 6 to 7 with sodium hydroxide is passed through SV500 [hr ^-1 ] every 30 minutes. Measure the Cu concentration [ppm] of the filtered water. From the obtained measurement results, the flow-through exchange capacity (C [eq]) when the flow-through point is 1.0 ppm and the total exchange capacity (C0 [eq]) of the ion exchange filter are calculated, and the flow-through exchange is performed by the following equation. Calculate the capacity ratio.
Flow exchange capacity ratio [%] = 100 x C / C0
(2) The ion exchange fiber according to (1), wherein the amount of carboxyl groups is 7.5 mmol / g or more.
(3) The ion exchange fiber according to (1) or (2), wherein at least a part of the carboxyl group is a calcium salt type carboxyl group.
(4) The ion exchange fiber according to (1) or (2), wherein at least a part of the carboxyl group is a magnesium salt type carboxyl group.
(5) A thread, non-woven fabric or papermaking sheet containing the ion exchange fiber according to any one of (1) to (4).
(6) The thread, non-woven fabric or papermaking sheet according to (5), wherein the content of the ion exchange fiber exceeds 20% by mass.
(7) An ion exchange filter comprising the thread, non-woven fabric or papermaking sheet according to (5) or (6).

Since the ion exchange fiber of the present invention employs a carboxyl group as an ion exchange group, trace heavy metal ions in hard water can be removed and recovered. Further, the fiber has a large amount of carboxyl groups, and has an extremely high specific surface area because of its fiber shape and fineness. Therefore, the fiber has a high probability of contact between the functional group and water when it is formed into a filter shape and passed through water, and heavy metal ions can be efficiently recovered and removed even under a high flow velocity. Further, when the ion exchange fiber of the present invention adopts a calcium salt or magnesium salt type carboxyl group, the degree of water swelling can be further lowered, so that when the mixing ratio when molding into a filter is designed to be high, Can also reduce pressure loss. The ion exchange fiber of the present invention having such performance can be used as, for example, a filter for industrial wastewater treatment containing heavy metals, which can cope with a high flow velocity.

It is a figure which shows the appearance of the ion exchange filter produced by winding the non-woven fabric using the ion exchange fiber of this invention. It is sectional drawing which looked at the filter housing which attached the ion exchange filter of FIG. 1 from the side. It is a graph which shows the measurement result of the once-through exchange capacity ratio in Examples 1 and 2 and Comparative Example 1. It is a graph which shows the measurement result of the Pb concentration in the filtered water in Example 1 and Comparative Example 1.

The present invention will be described in detail below. The ion exchange fiber of the present invention has a carboxyl group as an ion exchange group, and the amount of carboxyl thereof is 7.0 to 11.0 mmol / g, preferably 7.5 to 10.5 mmol / g, more preferably 7.5 to 10.5 mmol / g. Is 8.0 to 10.0 mmol / g. Here, the amount of carboxyl groups is measured by a method described later, and in the present invention, per 1 g of fibers of H-type carboxyl groups when various salt-type carboxyl groups are converted to H-type by acid. Indicates the amount. When the amount of the carboxyl group is less than 7.0 mmol / g, the total ion exchange capacity of the ion exchange filter containing the fiber decreases. If the amount of the carboxyl group exceeds 11.0 mmol / g, the durability of the fiber is remarkably lowered, and the yield at the time of producing the ion exchange filter is deteriorated. The amount of the carboxyl group can be controlled by adjusting the amount of the alkali metal compound used at the time of hydrolysis, which will be described later.

The carboxyl group contained in the ion exchange fiber of the present invention preferably has a structure salt-formed with calcium or magnesium. Since these are multivalent metal ions, they have the effect of forming an ionic bond between two carboxyl groups and reducing the degree of water swelling. On the other hand, when the carboxyl group is salt-formed with an alkali metal such as sodium or potassium, for example, the water permeability of the filter deteriorates and the pressure loss increases, which is not preferable. Further, in the case of polyvalent metals such as strontium, barium, and lanthanum, ionic bonds between carboxyl groups are formed, but the ions of these polyvalent metals have high selective adsorption property and are difficult to exchange ions, so Cu, Ni, and Pb. It is not preferable because it may not be able to adsorb ions and the like and it is economically disadvantageous.

Further, the ion exchange fiber of the present invention has a water swelling degree of 0.5 to 1.5 g / g, particularly preferably 0.8 to 1.2 g / g, as measured by a method described later. If the degree of water swelling exceeds 1.5 g / g, the water permeability of the ion exchange filter is lowered and pressure loss occurs, which is not preferable. Further, when the water swelling degree is less than 0.5 g / g, it is expected that almost no carboxyl group is introduced in the first place, and there is a possibility that the ion exchange performance cannot be exhibited. The degree of water swelling can be controlled by ionic bonding with the above-mentioned multivalent metal ions or by adjusting the amount of the cross-linking agent at the time of the cross-linking treatment in the production method described later.

Further, the ion exchange fiber of the present invention has a fineness of 1.0 to 3.0 dtex, particularly preferably 1.5 to 2.8 dtex. When the fineness exceeds 3.0 dtex, the contact probability between the carboxyl group and the heavy metal ion in water decreases due to the decrease in the specific surface area of the fiber, which may impair the ion exchange performance, which is not preferable. Further, when the fineness is less than 1.0 dtex, sufficient fiber strength cannot be maintained and the yield at the time of producing an ion exchange filter may deteriorate, which is not preferable.

Further, the ion exchange fiber of the present invention has a once-through exchange capacity ratio of 40% or more, preferably 50% or more, as measured by the method described in Examples described later. Here, the once-through exchange capacity refers to the exchange capacity until a certain concentration of leaked ions in the treated water (such a concentration is referred to as a once-through point) is reached when water is continuously passed. After passing the once-through point, ion exchange becomes insufficient and the number of leaked ions increases. Therefore, even if the total exchange capacity is not reached, the purpose such as ion removal cannot be achieved and the ion cannot be used substantially.

Further, the once-through exchange capacity ratio is the ratio of the once-through exchange capacity to the total exchange capacity, and is an index showing the speed of the ion exchange rate. Under the condition that water is flowing at a constant speed, the ion exchange rate gradually decreases as the ion exchange of the ion exchange group progresses. Eventually, the ion exchange rate does not match the flow velocity of the treatment liquid, and the ion exchange cannot be completed, reaching the once-through point. Therefore, the faster the initial ion exchange rate, the later the time to reach the once-through point, and the larger the once-through exchange capacity ratio.

When the once-through exchange capacity ratio is less than 40%, the ion exchange rate of the ion exchange fiber is low and the heavy metal removal performance is significantly lowered. Therefore, it is used under high flow velocity conditions or by a so-called one-pass in which the treatment liquid is passed only once. Not suitable for use. The flow-through exchange capacity ratio can also be adjusted by the fineness of the ion exchange fiber, and fineness is effective for improving the flow-through exchange capacity ratio.

The ion exchange filter in the present invention is a filter made by winding a thread, a non-woven fabric or a papermaking sheet made of a mixture containing ion exchange fibers, or a laminated non-woven fabric or a papermaking sheet and punching it into an arbitrary shape. Examples include, but are not limited to these.

The yarn used for producing the ion exchange filter in the present invention is not particularly limited, but is known such that the above-mentioned ion exchange fiber is mixed with other fibers, carded, and then spun as a sliver. Examples include threads obtained by the method.

The non-woven fabric for producing the ion exchange filter in the present invention is not particularly limited, but for example, the above-mentioned ion exchange fiber and other fibers are mixed and passed through a device such as a card machine a plurality of times to make a needle punch machine. , Non-woven fabric adjusted to an arbitrary density by passing through a calendar machine and the like can be mentioned.

The papermaking sheet for producing the ion exchange filter in the present invention is not particularly limited, but a slurry in which the above-mentioned mixture of ion exchange fibers and other fibers is uniformly dispersed using a beater, a refiner, or the like is produced. Then, the paper is made and then dried.

The other fibers in the above-mentioned yarn, non-woven fabric, and papermaking sheet are not particularly limited, and examples thereof include general-purpose fibers such as polyester and rayon, heat-sealing fibers, activated carbon fibers, and chelate fibers. The heat-fused fiber contributes to the improvement of moldability, and the fineness is preferably about 2 to 4 dtex, which is close to the ion exchange fiber to be mixed. Specific examples of such heat-sealed fibers include fibers having a core-sheath structure formed of polyethylene and polypropylene, polyester and polyethylene, polyester and low-melting point polyester, and the like. Further, when activated carbon fiber is mixed, dehalogenation performance can be imparted, and when chelate fiber is mixed, heavy metal in a region (several tens of ppb or less) having a lower concentration than when the ion exchange fiber of the present invention is used alone can be obtained. You will be able to remove it.

In addition, functional additives such as activated carbon, preservatives, antifungal agents, antibacterial agents, deodorants, and adsorbents are added to the above-mentioned threads, non-woven fabrics, papermaking sheets, or ion exchange filters formed by molding these. You may.

Further, in the above-mentioned yarn, non-woven fabric, and papermaking sheet, the content of the ion exchange fiber of the present invention is preferably more than 20% by mass, more preferably 25% by mass or more. If the content of the ion exchange fiber is less than the above lower limit, sufficient ion exchange performance may not be obtained.

Specific applications of the ion exchange filter of the present invention described above include a harmful heavy metal removal filter, a valuable metal recovery filter, a water purification filter and the like.

In the method for producing an ion exchange fiber of the present invention described above, an acrylic fiber having a fine fineness is used as a starting material, a crosslinked structure is formed in the fiber, and a carboxyl group is formed in the fiber at a high density by hydrolysis. , A method of forming a calcium salt type carboxyl group or a magnesium salt type carboxyl group by treating with a nitrate, sulfate, hydrochloride or the like of calcium or magnesium can be mentioned. The method will be described below.

First, the acrylic fiber used as a raw material is produced from an acrylonitrile-based polymer according to a known method, and the composition of the polymer is preferably 40% by mass or more of acrylonitrile, more preferably. It is 50% by mass or more, more preferably 80% by mass or more. Further, the fineness of the acrylic fiber may be any fineness such that the fineness of the finally obtained ion exchange fiber is 1.0 to 3.0 dtex, but usually, it is preferably 2.0 dtex or less. , More preferably 1.0 dtex or less. Since the fineness tends to increase due to the cross-linking treatment and the hydrolysis treatment described later, it is necessary to use an acrylic fiber having a finer fineness than the target fineness of the ion exchange fiber.

A crosslinked structure is introduced into the acrylic fiber as described above. A cross-linking agent such as a nitrogen-containing compound is preferably used for introducing the cross-linked structure. As the nitrogen-containing compound, it is preferable to use an amino compound having two or more primary amino groups or a hydrazine-based compound. After the crosslinked structure is introduced, a hydrolysis treatment with an alkali metal compound is performed to convert the nitrile group into a carboxyl group. The above-mentioned cross-linking treatment and hydrolysis treatment may be performed individually or at the same time. However, the conditions for each process differ depending on whether they are performed individually or at the same time.

The conditions for the cross-linking treatment when the cross-linking treatment and the hydrolysis treatment are individually performed are not limited as long as the ion-exchanged fibers of the present invention can be obtained. For example, when a hydrazine-based compound is used as the cross-linking agent, the hydrazine concentration is 10. Examples thereof include a method of immersing the above-mentioned acrylic fibers in an aqueous solution to which the above-mentioned hydrazine-based compound is added so as to have a concentration of about 18% by mass, and treating the mixture at 100 to 130 ° C. for 2 to 10 hours. Examples of the hydrolysis treatment conditions after the cross-linking treatment include a method of treating in an aqueous solution of a treatment agent containing 5 to 10% by mass of an alkali metal compound at a temperature of 100 to 130 ° C. for 2 to 10 hours.

The conditions for simultaneously performing the cross-linking treatment and the hydrolysis treatment are not particularly limited, but the amount of carboxyl groups required for the ion exchange fiber of the present invention is the same as the treatment conditions for each cross-linking hydrolysis described above. Select in consideration of such factors. In addition, it is possible to proceed with the reaction by reducing the amount of the drug as compared with the case of performing separately. For example, the acrylic fiber described above is immersed in an aqueous solution containing 0.5 to 4% by weight of a hydrazine compound as a cross-linking agent and 1 to 6% by weight of sodium hydroxide as an alkali metal compound, and the temperature is 100 to 130 ° C., 2 to 10%. Examples include a method of processing in time.

The carboxyl group after the hydrolysis treatment is the alkali metal used in the hydrolysis treatment as a counter ion. Here, by treating with an aqueous solution of calcium or magnesium nitrate, sulfate, hydrochloride or the like, conversion to calcium salt type carboxyl group or magnesium salt type carboxyl group can be performed. At this time, it is preferable to replace as many alkali metals as possible with calcium and magnesium salts by increasing the concentration of the aqueous solution. The specific treatment conditions are not particularly limited, but the temperature is 30 in an aqueous solution of a treatment agent containing 0.5 to 1.0 molar equivalents of calcium ions and magnesium ions with respect to the amount of the introduced carboxyl groups. Examples thereof include a method of treating at ~ 100 ° C. for 0.5 to 3 hours.

Since the ion exchange fiber of the present invention described above has a high carboxyl group amount, a large specific surface area, and a low water swelling degree, it has highly efficient ion exchange performance that could not be realized in the past. Therefore, the ion exchange filter using the ion exchange fiber of the present invention has a high exchange capacity like the conventional weakly acidic cation exchange resin and strongly acidic cation exchange resin, and Cu under high flow velocity conditions. It has become possible to remove heavy metal ions such as.

Examples are shown below to facilitate understanding of the present invention, but these are merely examples, and the gist of the present invention is not limited thereto. The evaluation method of the characteristics in the examples is as follows.

<Measurement method of carboxyl group amount>
About 1 g of the sample is weighed, immersed in 50 ml of 1 mol / l hydrochloric acid for 30 minutes, washed with water, and immersed in pure water at a bath ratio of 1: 500 for 15 minutes. After washing with water until the bath pH becomes 4 or more, it is dried at 105 ° C. for 5 hours in a hot air dryer. Approximately 0.2 g of the dried sample is precisely weighed (W1 [g]), 100 ml of water, 15 ml of 0.1 mol / l sodium hydroxide, and 0.4 g of sodium chloride are added thereto, and the mixture is stirred. Then, the sample is filtered out using a wire mesh and washed with water. Add 2 to 3 drops of phenolphthalein solution to the obtained filtrate (including washing solution) and titrate with 0.1 mol / l hydrochloric acid according to a conventional method to determine the amount of hydrochloric acid consumed (V1 [ml]). , The amount of carboxyl groups is calculated by the following formula.
Carboxylic acid group amount [mmol / g] = (0.1 × 15-0.1 × V1) / W1

<Measurement method of water swelling degree>
Approximately 1 g of a fully dried sample is precisely weighed (W2 [g]) and immersed in 200 ml of distilled water for 30 minutes. Then, dehydrate at 160 G (G indicates gravitational acceleration) for 5 minutes using a centrifugal dehydrator (TYPE KS-8000 manufactured by Kubota Co., Ltd.). The mass after dehydration is precisely weighed (W3 [g]), and the degree of water swelling is calculated by the following formula.
Water swelling degree [g / g] = (W3-W2) / W2

<Measurement method of fineness>
The measurement is performed by a method in accordance with "8.5 Fineness" of JIS L1015: 2010.

<Measurement method of once-through exchange capacity ratio>
Ion-exchange fiber sample (carboxyl group amount A1 [mmol / g]) and heat-sealed fiber (Unitika Melty 4080 fineness 2.2 dtex) are uniformly mixed using a roller card machine manufactured by KYOWA Machinery at a mass ratio of 3: 7. The mixture is passed through a needle punching machine and a calendar machine, and unnecessary parts are cut to obtain a non-woven fabric (length 100 cm, width 15 cm) having a thickness of 0.3 mm and a grain ratio of 100 g / m ² . Five pieces of this non-woven fabric are prepared, wrapped around a metal round bar having a diameter of 2.8 cm and a length of 30 cm, heated at 135 ° C. for 50 minutes, and by cutting unnecessary parts at the top and bottom, the inner diameter is 2.8 cm and the outer diameter is 5. Obtain an ion exchange filter as shown in FIG. 1 having a height of 6 cm and a height of 11.1 cm. The mass (W4 [g]) of the ion exchange filter is measured, and the total exchange capacity (C0 [eq]) of the ion exchange filter is calculated by the following equation.
C0 [eq] = A1 x W4 / 1000
Next, natural rubber packing (inner diameter 2.8 cm, outer diameter 6.3 cm, thickness 3 mm) was adhered to both end faces of the obtained ion exchange filter using a silicone sealant (manufactured by Cemedyne), and then FIG. As shown in, attach to the filter housing (manufactured by Nippon Filter Co., Ltd., product number NFH-A-5E), and use copper sulfate pentahydrate, calcium chloride dihydrate and sodium hydroxide to create a Cu concentration of 3 ppm and a Ca concentration. An aqueous solution adjusted to 12 ppm and pH 6 to 7 was passed through at SV (space velocity) 500 [hr ^-1 ], and the Cu concentration [ppm] of the filtered water was measured every 30 minutes by the method described below, and the Cu concentration was 1. Water is passed until it exceeds 0.0 ppm. The Cu concentration of the filtered water is plotted on the vertical axis, and the water flow rate ratio described later is plotted on the horizontal axis. From the graph connected by a straight line, the molar amount of Cu ions adsorbed by the ion exchange filter until the Cu concentration reaches 1.0 ppm Ask. Since Cu is a divalent ion, the value obtained by multiplying the obtained molar quantity by 2 is defined as the once-through exchange capacity (C [eq]), and the once-through exchange capacity is calculated by the following equation using the above total exchange capacity C0 [eq]. Calculate the ratio [%].
Flow exchange capacity ratio [%] = 100 x C / C0

The initial concentration of Cu and the permeation point in the above measurement method were set based on the NSF International Standard / American Standard (NSF / ANSI 53-2009) for drinking water treatment equipment.

<Measurement method of Cu concentration of filtered water>
The measurement is carried out by a method based on "24.3 Cuprizone Absorptiometry" of JISB8224: 2016.

<Measurement method of water flow ratio>
The apparent volume (Vi [l]) of the filter is calculated by subtracting the volume of the central cavity from the volume obtained from the external dimensions of the ion exchange filter used for measuring the once-through exchange capacity ratio. Using this value and the cumulative water flow (Vl [l]), the water flow ratio is calculated by the following formula.
Water flow ratio = Vl / Vi

<Measurement method of Pb concentration of filtered water>
A chromatographic column with a cock having an inner diameter of 4 cm is filled with 0.1 g of a sample, and 5 g of glass beads are placed therein. A test solution adjusted to a Pb concentration of 0.14 mg / l using lead nitrate was passed through the test solution at a flow rate of 25 ml / min up to a water flow rate of 4500 ml, and the concentration of the filtered water per hour was adjusted to "54. Measure by a method based on "4 ICP mass spectrometry".

[Example 1]
91% by mass of acrylonitrile and 9% by mass of methyl acrylate are polymerized to obtain an acrylonitrile-based polymer (extreme year [η] = 1.5 in dimethylformamide at 30 ° C.). A spinning stock solution prepared by dissolving 10 parts by mass of such a polymer in 90 parts by mass of a 48 mass% Rodin soda aqueous solution is spun and stretched (total draw ratio: 10 times) according to a conventional method, and then dry bulb / wet bulb = 120 ° C./60 ° C. After drying in the above atmosphere, a wet heat treatment was performed to obtain a raw material fiber (fiber length 70 mm) having a single fiber fineness of 0.9 dtex.

The raw material fibers were subjected to a treatment of simultaneously introducing cross-linking and hydrolysis at 115 ° C. for 3 hours in an aqueous solution containing 1.5% by mass of sodium hydroxide and 1.0% by mass of hydrated hydrazine, and washed with water. Then, it was treated with 8 mass% nitric acid aqueous solution at 120 degreeC for 3 hours, and was washed with water. Next, the obtained fiber was immersed in water, sodium hydroxide was added to adjust the pH to 9, and then the temperature was 70 ° C. in an aqueous solution in which calcium nitrate equivalent to 1.5 times the amount of carboxyl groups contained in the fiber was dissolved. The ion exchange treatment was carried out by immersing the mixture for 1 hour, and the mixture was washed with water and dried to obtain an ion exchange fiber containing a calcium salt-type carboxyl group. When various measurements were made on the ion-exchanged fibers, the amount of carboxyl groups was 8.0 mmol / g, the degree of water swelling was 1.0 g / g, the degree of fineness was 2.7 dtex, and the flow-through exchange capacity ratio was 60.2%. FIG. 3 shows a graph showing the relationship between the Cu concentration and the water flow rate ratio used for calculating the once-through exchange capacity ratio. The evaluation result of the Pb concentration in the filtered water is shown in FIG. The horizontal axis of FIG. 4 represents the water flow time in terms of the water flow amount.

[Example 2]
Using the same raw material fiber as that used in Example 1, a cross-linking introduction treatment was performed at 115 ° C. for 2 hours in an aqueous solution containing 15% by mass of hydrated hydrazine, and the fiber was washed with water. Next, hydrolysis treatment was performed at 120 ° C. for 2 hours in an aqueous solution containing 10% by mass of sodium hydroxide. Washed with water. Further, it was treated with a 6 mass% nitric acid aqueous solution at 110 ° C. for 3 hours and washed with water. Next, the hydrolysis treatment was performed again at 120 ° C. for 2 hours in an aqueous solution containing 3% by mass of sodium hydroxide, washed with water, and then treated with a 3% by mass nitric acid aqueous solution for 1 hour at 110 ° C. and washed with water. Next, the obtained fiber was immersed in water, sodium hydroxide was added to adjust the pH to 9, and then 70 ° C. × 70 ° C. in an aqueous solution in which calcium nitrate equivalent to twice the amount of carboxyl groups contained in the fiber was dissolved. Ion exchange treatment was carried out by immersing for 1 hour, and the ion exchange fiber having a calcium salt type carboxyl group was obtained by washing with water and drying. When various measurements were made on the ion-exchanged fibers, the amount of carboxyl groups was 8.9 mmol / g, the degree of water swelling was 1.1 g / g, the degree of fineness was 2.7 dtex, and the flow-through exchange capacity ratio was 52.7%. FIG. 3 shows a graph showing the relationship between the Cu concentration and the water flow rate ratio used for calculating the once-through exchange capacity ratio.

[Comparative Example 1]
Using a weakly acidic cation exchange resin (Dow Chemical Co., Ltd .: Dowex MAC-3, carboxyl group amount 5.7 mmol / g, particle size 0.3 to 1.2 mm, water swelling degree 2.0 g / g), This was filled in a column-type closed glass container to form an ion exchange resin tower. At this time, the total exchange capacity per volume of the ion exchange resin tower was 1.2 eq / l, and the total exchange capacity per volume of the ion exchange filter of Example 1 was 0.6 eq / l. In terms of conversion, it had twice the total exchange capacity. Using this ion exchange resin tower instead of the filter housing, the once-through exchange capacity ratio was measured in the same manner as in Example 1. The relationship between the Cu concentration obtained from this measurement and the water flow ratio is shown in FIG. The evaluation result of the Pb concentration in the filtered water is shown in FIG.

As can be seen from FIG. 3, since the ion exchange fiber of Example 1 has a fine fineness, the specific surface area is large, and up to a water flow ratio of about 3000, only about 0.1 ppm of Cu flows through, and almost all Cu is removed. You can see that it is made. Further, the once-through point (the point where the Cu concentration reaches 1 ppm) is about 4200 points with a water flow rate ratio, which tends to be relatively slow. The once-through exchange capacity ratio is 60.2%, and it can be seen that Cu can be efficiently removed, and that the material can be sufficiently used even under high flow velocity conditions in which Ca, which is a hardness component, coexists. In addition, Example 2 showed almost the same tendency as that of Example 1. On the other hand, since the ion exchange resin of Comparative Example 1 has a small specific surface area, about 0.5 ppm of Cu leaked from the initial stage of water flow. Further, as compared with Example 1, the flow point was reached earlier, and the subsequent increase in Cu concentration in the filtered water was gradual. The flow-through exchange capacity ratio is calculated to be 20.6%, which means that Cu cannot be removed efficiently, and it is found that it is not suitable for water treatment at a high flow velocity.

Further, as can be seen from FIG. 4, since the ion exchange fiber of Example 1 has a fineness and a large specific surface area, hardness components and other ions coexist, and even in a situation where the flow velocity is very high, Pb and the like can be used. Heavy metals can be removed efficiently. On the other hand, with respect to the ion exchange resin of Comparative Example 1, leakage of 0.02 ppm or more of Pb was observed from an early stage, and it was found that it was not suitable for water treatment at a high flow velocity.

1 ... Ion exchange filter 2 ... Cavity 3 ... Filter housing 4 ... Rubber packing 5 ... Flow of processing liquid

Claims

The amount of carboxyl groups was 7.0 to 11.0 mmol / g, the degree of water swelling was 0.5 to 1.5 g / g, and the fineness was 1.0 to 3.0 dtex, which were measured by the following methods. An ion exchange fiber having a once-through exchange capacity ratio of 40% or more.
(Method) An ion exchange filter made of a mixture of 30% by mass of ion exchange fibers and 70% by mass of heat-sealed fibers and having a density of 0.33 g / cm 3 was wound and then heat-bonded to prepare an ion exchange filter. The filter is attached to the filter housing, and an aqueous solution having a Cu concentration of 3 ppm and a Ca concentration of 12 ppm and adjusted to pH 6 to 7 with sodium hydroxide is passed through with SV500 [hr -1 ], and the Cu concentration of the filtered water [hr- 1 ] is passed every 30 minutes. ppm] is measured. From the obtained measurement results, the flow-through exchange capacity (C [eq]) when the flow-through point is 1.0 ppm and the total exchange capacity (C0 [eq]) of the ion exchange filter are calculated, and the flow-through exchange is performed by the following equation. Calculate the capacity ratio.
Flow exchange capacity ratio [%] = 100 x C / C0
The ion exchange fiber according to claim 1, wherein the amount of carboxyl groups is 7.5 mmol / g or more.
The ion exchange fiber according to claim 1 or 2, wherein at least a part of the carboxyl groups is a calcium salt type carboxyl group.
The ion exchange fiber according to claim 1 or 2, wherein at least a part of the carboxyl groups is a magnesium type carboxyl group.
A thread, non-woven fabric or papermaking sheet containing the ion exchange fiber according to any one of claims 1 to 4.
The thread, non-woven fabric or papermaking sheet according to claim 5, wherein the content of the ion exchange fiber exceeds 20% by mass.
An ion exchange filter comprising the thread, non-woven fabric or papermaking sheet according to claim 5 or 6.