Behavior of Trace Amounts of Cd and Zn in Sorption and Coprecipitation in Tetrahydrofuran Solutions

Sorption of trace amounts of Cd-109 and Zn-65 on zeolites NaX and NaA in the presence of divalent lanthanides Ln(2+) (Ln = Tm, Dy, Nd) from tetrahydrofuran (THF) solutions is studied. In contrast to Cs-137(+) and similar to Sr-85(2+), trace amounts of Cd-109 and Zn-65 are not practically sorbed on zeolites (about 99% of these radionuclides remains in the solution). The distribution coefficients K-d of Cd-109 and Zn-65 are similar to 0.3 and similar to 0.4 ml g(-1), respectively. In THF solutions, Tm2+ is oxidized to Tm3+, and TmI3 center dot 3THF is precipitated. Study of cocrystallization of trace amounts of Cd-109 and Zn-65 and also of Sr-85 with this precipitate from THF solutions containing Tm2+ revealed that, in contrast to Sr-85(2+), Cd-109 and Zn-65 traces cocrystallize with the solid solvate phase. The cocrystallization coefficients D of Cd-109 and Zn-65 increase with increasing Tm3+/Tm2+ ratio in the solution. The mechanism suggested is that, in the presence of Tm2+, Cd-109(2+) and Zn-65(2+) are reduced to single-charged cations M+, which then rapidly react with the double-charged cations M2+ with the formation of dimers M-2(3+) (M = Cd, Zn).