Patent Number: 054769892
Section: description

The following examples are provided to further illustrate the present invention. It is to be understood, however, that the examples are presented for purpose of illustration only and are not intended as limiting the invention. Unless otherwise indicated, all parts, percents, ratios and the like are by weight. EXAMPLE 1 A 1 liter capacity beaker was charged with 30 ml of plutonium-bearing liquid waste adjusted to pH 1.6 having a uranium (referred to as "U" hereinafter) concentration of 3.3.times.10.sup.-2 mg/ml and a plutonium (referred to as "Pu" hereinafter) concentration of 3.18.times.10.sup.-3 mg/ml and then with 1.0 g of a fibrous active carbon preparation (manufactured by UNITIKA, LTD. under the trade name of A-20; specific surface area, 2,100 m.sup.2 /g; ignition point, 480.degree. C.; equilibrium moisture regain, 11% at a relative humidity of 45%), and the resulting mixture was subjected to an adsorption treatment at a temperature of 25.degree. C. for 24 hours. This fibrous active carbon adsorbed Pu in an amount of 9.4.times.10.sup.-2 mg/g, with an adsorption percentage of 99%. After the adsorption treatment, the spent fibrous active carbon was dehydrated, dried and then put in a melting pot for incineration for 3 hours of at 600.degree. C. When burned, the fibrous active carbon became red but emitting no flames, and its quantity decreased over time. The residue after incineration was only about 1 mg, and no scattering of radioactive materials was detected. EXAMPLE 2 A 94 g portion of phenol was put in a 5 liter capacity beaker. With stirring, to this was gradually added 170 g of 98% concentrated sulfuric acid while keeping the phenol temperature at 50.degree. C. or below. To the resulting mixture was further added 9 ml of 37% formaldehyde in the same method, followed by 1 hour of reaction at 70.degree. C. The resulting reaction solution was immediately cooled to room temperature (about 20.degree.-30.degree. C.). To a 72 g portion of the reaction solution was added a mixture of 17.4 g phosphorous acid and 6.2 g ion-exchanged water with stirring, followed by the addition of 74 ml of 37% formaldehyde in the same method. The resulting solution was diluted with 300 ml of water and then mixed with 30 g of a fibrous active carbon preparation (manufactured by UNITIKA, LTD. under the trade name of A-20; specific surface area, 2,110 m.sup.2 /g). After allowing the fibrous active carbon to contact the reaction solution thoroughly, 9.9 ml of diethylenetriamine was immediately added to the mixture. After 3 hours of reaction at 80.degree. C., the liquid portion of the reaction mixture was removed, and the remaining reaction product was washed with water and then dried at 100.degree. C. for 1.5 hours to obtain a fibrous active carbon preparation (Sample A) to which aminomethylphosphonic acid functional groups had been added. Sample A had a specific surface area of 1,014 m.sup.2 /g, an ignition point of 480.degree. C. and an equilibrium moisture regain of 43% at a relative humidity of 45%. A 1 g portion of Sample A was placed in a 1 liter capacity beaker containing 80 ml of the same plutonium-bearing liquid waste as described in Example 1, and the adsorption treatment of Example 1 was repeated. Sample A adsorbed Pu in an amount of about 2.3.times.10.sup.-1 mg/g, with an adsorption percentage of 90%. After the adsorption treatment, the spent Sample A was dehydrated, dried and then placed in a melting pot for incineration at 600.degree. C. for 3 hours. When burned, similar to the case of the fibrous active carbon, Sample A became red but with no emission of flames, and its quantity decreased over time. The residue after the incineration was about 1 mg or less, and no scattering of radioactive materials was detected. COMPARATIVE EXAMPLE 1 An adsorption treatment of plutonium-bearing liquid waste was carried out in the same method as described in Example 2, except that 1.0 g of a commercially available coconut shell active carbon preparation (granular; specific surface area, 800 m.sup.2 /g; ignition point, 510.degree. C.) was used. The granular active carbon adsorbed Pu in an amount of about 4.3.times.10.sup.-2 mg/g, with an adsorption percentage of 17%. After the adsorption treatment, the spent granular active carbon was dehydrated, dried and then placed in a melting pot for incineration at 600.degree. C. for 3 hours. The granular active carbon burned with the emission of flames. About 35 mg of material remained after the incineration as the burning residue of the active carbon, and scattering of radioactive materials was detected around the melting pot. COMPARATIVE EXAMPLE 2 An adsorption treatment of plutonium-bearing liquid waste was carried out in the same method as described in Example 2, except for the use of 1.0 g of a commercially available chelate resin with aminomethylphosphonic acid functional groups (Unicelec UR-3100, manufactured by UNITIKA, LTD.). The chelate resin adsorbed Pu in an amount of 2.0.times.10.sup.-1 mg/g, with an adsorption percentage of 78%. After the adsorption treatment, the spent chelate resin was dehydrated and placed in a melting pot for incineration at 900.degree. C. for 5 hours. The chelate burned giving forth smoke and flames. About 90 mg of materials remained after the incineration as a foamed carbonized residue which stuck fast to the wall of the melting pot, thus showing extreme difficulty in carrying out the waste treatment. In addition, a large amount of scattering of radioactive nuclides was detected around the melting pot. EXAMPLE 3 A glass column having an inside diameter of 14.8 mm and a height of 500 mm was packed with 9.0 g of a fibrous active carbon preparation (manufactured by UNITIKA, LTD. under the trade name of A-20; specific surface area, 2,100 m.sup.2 /g; ignition point, 480.degree. C.; equilibrium moisture regain, 11% at a relative humidity of 45%). The resulting packed layer had a height of 400 mm. A 400 ml portion of plutonium-bearing liquid waste having a U concentration of 0.26 mg/ml and a Pu concentration of 3.9.times.10.sup.-5 mg/ml was passed through the thus prepared column at a flow rate of 176 ml/hr. As a result, the packed fibrous active carbon adsorbed 10.0.times.10.sup.-3 mg of Pu with an adsorption percentage of 64%, and 46 mg of U with an adsorption percentage of 44%. After the adsorption treatment, the spent fibrous active carbon was dehydrated, dried and then placed in a melting pot for 3 hours of incineration at 550.degree. C. When burned, the fibrous active carbon became red but emitting no flames, and its quantity decreased over time. The residue after the incineration was about 47 mg, and no scattering of radioactive materials was detected. EXAMPLE 4 The column process of the plutonium-bearing liquid waste of Example 3 was repeated except that Sample A prepared in Example 2 was used as the adsorbent. As a result, the packed Sample A adsorbed 10.0.times.10.sup.-3 mg of Pu with an adsorption percentage of 64%, and 40 mg of U with an adsorption percentage of 39%. After the adsorption treatment, spent Sample A was dehydrated, dried and then placed in a melting pot to for 3 hours of incineration at 600.degree. C. When burned, similar to the case of the fibrous active carbon, Sample A became red but emitting no flames, and its quantity decreased over time. The residue after the incineration was about 41 mg, and no scattering of radioactive materials was detected. EXAMPLE 5 A 3 g portion of a fibrous active carbon preparation (manufactured by UNITIKA, LTD. under the trade name of A-20; specific surface area, 2,116 m.sup.2 /g) was placed in an electric furnace controlled at 600.degree. C. and subjected to 10 minutes of oxidation reaction to obtain an oxidized active carbon adsorbent. The thus obtained adsorbent was found to have a specific surface area of 2,071 m.sup.2 /g, an ignition point of 480.degree. C. and an equilibrium moisture regain of 53% at a relative humidity of 45%. A 0.25 g portion of the adsorbent was soaked in 50 ml of Pu solution having a Pu concentration of 5.0.times.10.sup.-3 mg/ml and an acid concentration of 1.0N, followed by 120 hours of adsorption treatment. As a result, a Pu-adsorption percentage of 96.1% was obtained. After the adsorption treatment, the spent fibrous active carbon was dehydrated, dried and then placed in a melting pot to for 3 hours of incineration at 600.degree. C. When burned, the fibrous active carbon became red but emitting no flames, and its quantity decreased over time. The residue after the incineration was 1 mg or less, and no scattering of radioactive materials was detected. EXAMPLE 6 A 8 g portion of polyethyleneimine having a molecular weight of 600 (Epomin PEI-600, manufactured by Japan Catalytic Chemical Industry Co., Ltd.) was dissolved in 4.5 liters of ion-exchanged water, and 100 g of a fibrous active carbon preparation (manufactured by UNITIKA, LTD. under a trade name of A-20; specific surface area, 2,110 m.sup.2 /g) was soaked in the polyethyleneimine solution. After standing for 4 hours, 3 g of carbon disulfide was added to the resulting mixture and the mixture was gently stirred at room temperature. When emulsion state of the liquid phase disappeared, the temperature of the mixture was increased to 80.degree. C. and the reaction was continued for 4 hours. After removing the liquid portion, the resulting reaction product was washed thoroughly with hot water and then dried at 50.degree. C. for 4 hours to obtain an adsorbent to which polyethyleneimine functional groups have been added. The thus obtained adsorbent was found to have a specific surface area of 1,420 m.sup.2 /g, an ignition point of 480.degree. C. and an equilibrium moisture regain of 48% at a relative humidity of 45%. An adsorption treatment of a Pu solution was carried out in the same method as in Example 5 except that 0.25 g of the thus obtained adsorbent was used. As a result, a Pu-adsorption percentage of 88.3% was obtained. After the adsorption treatment of the functional group-added adsorbent, the spent adsorbent was dehydrated, dried and then placed in a melting pot for 3 hours of incineration at 600.degree. C. When burned, the functional group-added adsorbent became red but emitting no flames, and its quantity decreased over time. The residue after the incineration was 1 mg or less, and no scattering of radioactive materials was detected. EXAMPLE 7 A 94 g portion of phenol was placed in a 5 liter capacity beaker. With stirring, to this was gradually added 170 g of 98% concentrated sulfuric acid while keeping the phenol temperature at 50.degree. C. or below. To the resulting mixture was further added 9 ml of 37% formaldehyde in the same method, followed by 1 hour of reaction at 70.degree. C. The resulting reaction solution was immediately cooled to room temperature. To a 8.7 g portion of the reaction solution was added a mixture of 2.1 g phosphorous acid and 0.75 g ion-exchanged water with stirring, followed by the addition of 9.0 ml of 37% formaldehyde in the same method. The resulting solution was diluted with 1,500 ml of water and then mixed with 30 g of a fibrous active carbon preparation (manufactured by UNITIKA, LTD. under the trade name of A-20; specific surface area, 2,110 m.sup.2 /g). After allowing the fibrous active carbon to contact thoroughly the reaction solution, 1.2 ml of diethylenetriamine was immediately added to the mixture. After 3 hours of reaction at 80.degree. C., the liquid portion of the reaction mixture was removed, and the remaining reaction product was washed with water and then dried at 125.degree. C. for 2 hours to obtain a fibrous active carbon preparation to which aminomethylphosphonic acid functional groups had been added. The thus obtained adsorbent showed a specific surface area of 1,280 m.sup.2 /g, an ignition point of 480.degree. C. and an equilibrium moisture regain of 41% at a relative humidity of 45%. An adsorption treatment of a Pu solution was carried out in the same method as in Example 5 except that 0.25 g of the thus obtained adsorbent was used. As a result, a Pu-adsorption percentage of 86.8% was obtained. After the adsorption treatment of the functional group-added adsorbent, the spent adsorbent was dehydrated, dried and then placed in a melting pot for 3 hours of incineration at 600.degree. C. When burned, the functional group-added adsorbent became red but with no emission of flames, and its quantity decreased over time. The residue after the incineration was about 1 mg or less, and no scattering of radioactive materials was detected. COMPARATIVE EXAMPLE 3 An adsorption treatment of a plutonium-bearing solution was carried out in the same method as described in Example 5, except that a fibrous active carbon preparation (A-10, manufactured by UNITIKA, LTD.) having a specific surface area of 950 m.sup.2 /g, an ignition point of 480.degree. C. and an equilibrium moisture regain of 31% at a relative humidity of 45% was used as the adsorbent. As a result, the adsorption percentage of Pu was found to be only 60%. COMPARATIVE EXAMPLE 4 A 10 g portion of a fibrous active carbon preparation (manufactured by UNITIKA, LTD. under the trade name of A-20; specific surface area, 2,116 m.sup.2 /g) was placed in an electric tube furnace. On passing hydrogen gas through the furnace at a flow rate of 75 ml/min, the temperature of the furnace was increased to 900.degree. C. at a rate of increase of 300.degree. C./hr and the fibrous active carbon was subjected to 15 minutes of a reduction treatment at the same final temperature. The reduction-treated active carbon adsorbent thus obtained had a specific surface area of 2,060 m.sup.2 /g, an ignition point of 480.degree. C. and an equilibrium moisture regain of 0.9% at a relative humidity of 45%. An adsorption treatment of a plutonium-bearing solution was carried out in the same method as described in Example 5, except that the thus obtained adsorbent was used. As a result, the adsorption percentage of Pu was found to be only 50%. Thus, it is apparent that, in accordance with the present invention, an adsorbent useful for the selective adsorption of radioactive nuclides, as well as a process for the volume reduction of radioactive waste that contains radioactive nuclides are provided. Since the adsorbent of the present invention which comprises a fibrous active carbon system having an inorganic framework and a specific surface area of 1,000 m.sup.2 /g or more has a hydrophilic property due to its oxidation treatment, etc. the adsorbent of the present invention possesses excellent durability against radiation and adsorbs transuranium elements selectively. As a consequence, the use of the inventive adsorbent in the treatment process of radioactive liquid waste renders possible the selective and secure separation and removal of trace amounts of plutonium and the like from the radioactive liquid waste. Also, according to the present invention, the volume of radioactive nuclides-adsorbed waste can be reduced significantly and scattering of radioactive nuclides at the time of incineration can be prevented, without a problem of securing extra storage space due to increased amounts of waste occurring. While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.