Metal adsorption acrylic fiber, non-woven fabric, sheet-like product, and uses thereof as metal adsorbent

1. A metal adsorption acrylic fiber, wherein:

said fiber consists of an acrylonitrile-based copolymer comprising at least 85 mass % of a component unit derived from acrylonitrile and component units derived from vinyl acetate and sodium methallylsulfonate and 30-300 mass % of water relative to the mass of the acrylonitrile-based copolymer; and

said fiber has a BET specific surface area of 50 to 500 m 2 /g, a SAG value of 2 to 20, and a strontium adsorption rate of 85% or more;

wherein the SAG value represents an amount of acidic terminal groups in said copolymer and is determined by a measurement method comprising:

X g of the metal adsorption acrylic fiber is dissolved in 50 ml of dimethylformamide, and passed through an ion exchange resin to give a free acid after which neutralization titration is performed with A ml of a 0.01 N potassium hydroxide/methanol solution until pH 7 is reached;

separately, 50 ml of dimethylformamide which does not contain the metal adsorption acrylic fiber is taken as a blank and passed through the ion exchange resin after which neutralization titration is performed with B ml of a 0.01 N potassium hydroxide/methanol solution until pH 7 is reached; and

the SAG value is calculated using the following equation:

SAG value (equivalent g/g )=( A−B )/ X×f× 10 −5

where f=a titer of the 0.01 N potassium hydroxide/methanol solution;

and wherein the strontium adsorption rate is measured by a measurement method comprising:

adding 5 g of the metal adsorption acrylic fiber, which has been vacuum dried, to a 1000 mL capacity fluorine resin container, then adding 500 mL of an immersion liquid at 20° C. to the container to start immersion of the metal adsorption acrylic fiber, wherein the immersion liquid comprises an aqueous solution of strontium carbonate with a concentration of 0.1 ppm;

agitating the container for 24 hours after the start of immersion, while maintaining a temperature of the immersion liquid at 20° C., and then collecting the immersion liquid as a test liquid;

introducing the test liquid into an inductively-coupled plasma mass spectrometer, and quantitatively measuring a concentration of strontium C 1 (ppm) in the test liquid; and

adding 500 mL of the immersion liquid at 20° C., without the metal adsorption acrylic fiber, to another container to give a reference liquid, and quantitatively measuring a concentration of strontium C 2 (ppm) in the reference liquid;

wherein the strontium adsorption rate of the metal adsorption acrylic fiber is given by:

strontium adsorption rate (%)={(C 2 −C 1 )/C 2 }×100.

2. The metal adsorption acrylic fiber according to claim 1 , wherein said fiber has a cesium adsorption rate that is 70% or more, wherein the cesium adsorption rate is measured by a measurement method comprising:

adding 5 g of the metal adsorption acrylic fiber, which has been vacuum dried, to a 1000 mL capacity fluorine resin container, then adding 500 mL of an immersion liquid at 20° C. to the container to start immersion of the metal adsorption acrylic fiber, wherein the immersion liquid comprises an aqueous solution of cesium chloride with a concentration of 0.1 ppm;

agitating the container for 24 hours after the start of immersion, while maintaining a temperature of the immersion liquid at 20° C., and then collecting the immersion liquid as a test liquid;

introducing the test liquid into an inductively-coupled plasma mass spectrometer, and quantitatively measuring a concentration of cesium C 3 (ppm) in the test liquid; and

adding 500 mL of the immersion liquid at 20° C., without the metal adsorption acrylic fiber, to another container to give a reference liquid, and quantitatively measuring a concentration of cesium C 4 (ppm) in the reference liquid;

wherein the cesium adsorption rate of the metal adsorption acrylic fiber is given by:

cesium adsorption rate (%)={(C 4 −C 3 )/C 4 }×100.

3. The metal adsorption acrylic fiber according to claim 1 , wherein said fiber has a cerium adsorption rate that is 85% or more, wherein the cerium adsorption rate is measured by a measurement method comprising:

adding 5 g of the metal adsorption acrylic fiber, which has been vacuum dried, to a 1000 mL capacity fluorine resin container, then adding 500 mL of an immersion liquid at 20° C. to the container to start immersion of the metal adsorption acrylic fiber, wherein the immersion liquid comprises an aqueous solution of cerium chloride (III) heptahydrate with a concentration of 0.1 ppm;

agitating the container for 24 hours after the start of immersion, while maintaining a temperature of the immersion liquid at 20° C., and then collecting the immersion liquid as a test liquid;

introducing the test liquid into an inductively-coupled plasma mass spectrometer, and quantitatively measuring a concentration of cerium C 5 (ppm) in the test liquid; and

adding 500 mL of the immersion liquid at 20° C., without the metal adsorption acrylic fiber, to another container to give a reference liquid, and quantitatively measuring a concentration of cerium C 6 (ppm) in the reference liquid;

wherein the cerium adsorption rate of the metal adsorption acrylic fiber is given by:

cerium adsorption rate (%)={(C 6 −C 5 )/C 6 }×100.

4. The metal adsorption acrylic fiber according to claim 1 , wherein the fiber has a second strontium adsorption rate that is 70% or more, wherein the second strontium adsorption rate is measured by a measurement method comprising:

adding 5 g of the metal adsorption acrylic fiber, which has been vacuum dried, to a 1000 mL capacity fluorine resin container, then adding 500 mL of an immersion liquid at 20° C. to the container to start immersion of the metal adsorption acrylic fiber, wherein the immersion liquid comprises an aqueous solution of strontium carbonate with a concentration of 1.0 ppm;

agitating the container for 24 hours after the start of immersion, while maintaining a temperature of the immersion liquid at 20° C., and then collecting the immersion liquid as a test liquid;

introducing the test liquid into an inductively-coupled plasma mass spectrometer, and quantitatively measuring a concentration of strontium C 7 (ppm) in the test liquid; and

adding 500 mL of the immersion liquid at 20° C., without the metal adsorption acrylic fiber, to another container to give a reference liquid, and quantitatively measuring a concentration of strontium C 8 (ppm) in the reference liquid;

wherein the second strontium adsorption rate of the metal adsorption acrylic fiber is given by:

second strontium adsorption rate (%)={(C 8 −C 7 )/C 8 }×100.

5. The metal adsorption acrylic fiber according to claim 1 , wherein said fiber has a second cesium adsorption rate that is 70% or more, wherein the second cesium adsorption rate is measured by a measurement method comprising:

adding 5 g of the metal adsorption acrylic fiber, which has been vacuum dried, to a 1000 mL capacity fluorine resin container, then adding 500 mL of an immersion liquid at 20°C. to the container to start immersion of the metal adsorption acrylic fiber, wherein the immersion liquid comprises an aqueous solution of cesium chloride with a concentration of 1.0 ppm;

agitating the container for 24 hours after the start of immersion, while maintaining a temperature of the immersion liquid at 20° C., and then collecting the immersion liquid as a test liquid;

introducing the test liquid into an inductively-coupled plasma mass spectrometer, and quantitatively measuring a concentration of cesium C 9 (ppm) in the test liquid; and

adding 500 mL of the immersion liquid at 20° C., without the metal adsorption acrylic fiber, to another container to give a reference liquid, and quantitatively measuring a concentration of cesium C 10 (ppm) in the reference liquid;

wherein the second cesium adsorption rate of the metal adsorption acrylic fiber is given by:

second cesium adsorption rate (%)={(C 10 −C 9 )/C 10 }×100.

6. The metal adsorption acrylic fiber according to claim 1 , wherein the BET specific surface area is 100 to 160 m 2 /g.

7. The metal adsorption acrylic fiber according to claim 6 , wherein the SAG value is 2.5 to 16.

8. The metal adsorption acrylic fiber according to claim 1 , wherein the BET specific surface area is 80 to 200 m 2 /g.

9. The metal adsorption acrylic fiber according to claim 1 , which is obtained by wet-spinning a spinning dope obtained by dissolving the acrylonitrile-based copolymer in a solvent into a solidifying liquid, and performing stretching and washing without dry densification treatment.

10. A sheet-like product comprising the metal adsorption acrylic fiber according to claim 1 .

11. A non-woven fabric comprising the metal adsorption acrylic fiber according to claim 1 .

12. The non-woven fabric according to claim 11 , having a weight per area of 50 to 1000 g/m 2 and a density of 0.05 to 0.5 g/cm 3 .

13. A metal adsorbent comprising the metal adsorption acrylic fiber according to claim 1 .

14. A metal adsorbent comprising the sheet-like product according to claim 10 .

15. A metal adsorbent comprising the non-woven fabric according to claim 11 .

16. The metal adsorption acrylic fiber according to claim 1 , wherein the acrylonitrile-based copolymer consists of at least 85 mass % of a component unit derived from acrylonitrile and component units derived from vinyl acetate and sodium methallylsulfonate.

17. The metal adsorption acrylic fiber according to claim 1 , wherein the acrylonitrile-based copolymer consists of at least 87 mass % of a component unit derived from acrylonitrile and component units derived from vinyl acetate and sodium methallylsulfonate.

18. The metal adsorption acrylic fiber according to claim 1 , wherein said fiber has a BET specific surface area of 80 to 200 m 2 /g, a SAG value of 2.5 to 16, and a strontium adsorption rate of 90-100%.