Design and use of redox-recyclable organometallic extractants for the cationic radionuclides Cs-137(+) and Sr-90(2+) from waste solutions

Two new redox-active organometallic extractants for the redox-recyclable ex traction and recovery ((RER)-E-2) of the cationic radionuclides Cs-137(+) a nd Sr-90(2+) from aqueous waste simulants, Na[Fe(eta(5)-C5H5)(eta(5)-(3)-1, 2-C2B9H9(n-C12H25)(2))] (Na+I-) and Na[Fe(eta(5)-C5H5)(eta(5)-(3)-1,2-C2B9H 7(n-C12H25)(2)-9,12-Br-2)] (Na+II-), were synthesized and investigated. Whe n diluted with toluene or xylenes, they extracted Cs+ from aqueous waste si mulants such as (i) 1 mol L-1 NaOH + 1 mol L-1 NaNO3, (ii) 1 mol L-1 HNO3, and/or (iii) 1 mol L-1 NaCl, with D(Cs) values that ranged from 5 to 20; th e corresponding D(Sr) values were less than or equal to 0.04. The addition of poly(ethylene glycol) as a co-diluent increased D(Sr) values to as high as 33 but decreased D(Cs) values by a factor of 2-10, depending on conditio ns. When separated from the raffinate and exposed to air, the extractant-co ntaining organic phase released greater than or equal to 88% of its radioac tivity in the form of a solid precipitate of minimal volume. When a small a mount of water was present during this procedure, the extractant-containing organic phase released greater than or equal to 99% of its radioactivity t o the new aqueous phase. When an oxidized dilute extractant was rereduced a nd used for a second (RER)-E-2 cycle, the D(Cs) value was unchanged.