Adsorbent for radioelement-containing waste and method for fixing radioelement

Abstract

An adsorbent for radioelement-containing waste includes spherical layered double hydroxide (A) or spherical metal hydroxide (B). (A) is a nonstoichiometric compound represented by general formula (a) or (b): [M 2+ 1-x M 3+ x (OH) 2 ] x+ [A n− x/n .m H 2 O] x−   (a), [Al 2 Li(OH) 6 ] x+ [A n− x/n .m H 2 O] x−   (b) where 0.1≦x≦0.4, 0<m. The n represents a natural number of 1 to 4, M 2+ represents at least one divalent metal, M 3+ represents at least one trivalent metal, and A n− represents at least one n-valent ion-exchangeable anion. (B) contains a metal selected from the group of Group II, Group IV, Group V, Group VI, Group XI, Group XII, and Group XIII of the periodic table, and the group of Mn, Fe, Co, Ni, Pb, and Bi. This adsorbent efficiently adsorbs and collects volatile iodine, a radioactive anion in wastewater, etc. providing a crack-resistant solidified article after a solidification treatment, and effectively confines the radioelement-containing waste with long-term stability.

1 . An adsorbent for a radioelement of a long half-life radioelement-containing waste, or for cation species or anion species containing radionuclides in water in a system in a nuclear power plant comprising hydroxide in spherical powder form containing a metal selected from the group consisting of the metal atoms belonging to Group II, Group IV Group V, Group VI, Group XI, Group XII and Group XIII of the periodic table, and the group consisting of Mn, Fe, Co, Ni, Pb, and Bi. 
     
     
         2 . The adsorbent for radioelement-containing waste according to  claim 1 , wherein the metal hydroxide in spherical powder form comprises aluminum hydroxide, magnesium hydroxide, iron (II) hydroxide, iron (III) hydroxide oxide, or iron (III) hydroxide. 
     
     
         3 . The adsorbent for radioelement-containing waste according to  claim 1  wherein the metal hydroxide in spherical powder form has an average particle diameter in the range of 1.0 to 200 μm. 
     
     
         4 . The adsorbent for radioelement-containing waste according to  claim 1 , wherein the surface of the metal hydroxide in spherical powder form is subjected to a hydrophobic treatment. 
     
     
         5 . The adsorbent for radioelement-containing waste according to  claim 4 , wherein the hydrophobic treatment is performed with a silanizing agent. 
     
     
         6 . The adsorbent for radioelement-containing waste according to  claim 5 , wherein the silanizing agent is represented by the following formula:
   R 4-n SiX n ,   wherein n=1, 2, or 3, and   wherein R represents a hydrocarbon group having 1 to 32 carbon atoms and some of or all of the hydrogen atoms of the hydrocarbon group may be substituted with fluorine atoms, however, a compound wherein the number of carbons is 1 and n=1 is eliminated; and X represents an alkoxy group, a hydrogen atom, a hydroxyl group, a phenoxy group, or a diethylamino group.   
     
     
         7 . A method of fixing a radioelement comprising allowing a metal hydroxide in spherical powder form to adsorb the radioelement, forming a compact of a composite powder composed of the spherical metal hydroxide powder (A) that has adsorbed the radioelement and a fixing agent (B) under pressure, and sintering the compact at a predetermined temperature. 
     
     
         8 . The method of fixing a radioelement according to  claim 7 , wherein, in the composition of the composite powder, the mixing ratio of the spherical metal hydroxide powder (A) that has adsorbed a radioelement to the fixing agent (B) is in the range of (A):(B) 5:95 to 60:40 in terms of the mass ratio. 
     
     
         9 . The method of fixing radioelement-containing waste according to  claim 7 , wherein a sintered article is produced by processing the pressure-formed compact with microwaves. 
     
     
         10 . The method of fixing radioelement-containing waste according to  claim 7 , wherein a compact is formed by compressing the composite powder composed of the spherical metal hydroxide powder (A) that has adsorbed the radioelement and a fixing agent (B) under a predetermined pressure, and the compact is heats to a predetermined temperature by applying a pulse voltage. 
     
     
         11 . The method of fixing a radioelement according to  claim 7 , wherein the fixing agent is a calcium phosphate ceramic. 
     
     
         12 . The method of fixing a radioelement according to  claim 11 , wherein the calcium phosphate ceramic is at least one of hydroxyapatite and fluorapatite. 
     
     
         13 . The method of fixing a radioelement according to  claim 10 , wherein the predetermined pressure applied to the composite powder is in the range of 5 to 100 MPa. 
     
     
         14 . The method of fixing a radioelement according to  claim 7 , wherein the sintering temperature of the composite powder is in the range of 700° C. to 1,200° C.