Design and Use of Redox-Recyclable Organometallic Extractants for the Cationic Radionuclides 137Cs+ and 90Sr2+ from Waste Solutions

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Two new redox-active organometallic extractants for the redox-recyclable extraction and recovery (R 2 ER) of the cationic radionuclides 137 Cs + and 90 Sr 2+ from aqueous waste simulants, Na[Fe(η 5 -C 5 H 5 )(η 5 -(3)-1,2-C 2 B 9 H 9 ( n- C 12 H 25 ) 2 )] (Na + I - ) and Na[Fe(η 5 -C 5 H 5 )(η 5 -(3)-1,2-C 2 B 9 H 7 ( n- C 12 H 25 ) 2 -9,12-Br 2 )] (Na + II - ), were synthesized and investigated. When diluted with toluene or xylenes, they extracted Cs + from aqueous waste simulants such as (i) 1 mol L - 1 NaOH + 1 mol L - 1 NaNO 3, (ii) 1 mol L - 1 HNO 3, and/or (iii) 1 mol L - 1 NaCl, with D (Cs) values that ranged from 5 to 20; the corresponding D (Sr) values were ≤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 conditions. When separated from the raffinate and exposed to air, the extractant-containing organic phase released ≥88% of its radioactivity in the form of a solid precipitate of minimal volume. When a small amount of water was present during this procedure, the extractant-containing organic phase released ≥99% of its radioactivity to the new aqueous phase. When an oxidized dilute extractant was rereduced and used for a second R 2 ER cycle, the D (Cs) value was unchanged.