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

Abstract

Sorption of trace amounts of 109Cd and 65Zn on zeolites NaX and NaA in the presence of divalent lanthanides Ln2+ (Ln = Tm, Dy, Nd) from tetrahydrofuran (THF) solutions is studied. In contrast to 137Cs+ and similar to 85Sr2+, trace amounts of 109Cd and 65Zn are not practically sorbed on zeolites (about 99% of these radionuclides remains in the solution). The distribution coefficients Kd of 109Cd and 65Zn are ∼0.3 and ∼0.4 ml g−1, respectively. In THF solutions, Tm2+ is oxidized to Tm3+, and TmI3 ⋅ 3THF is precipitated. Study of cocrystallization of trace amounts of 109Cd and 65Zn and also of 85Sr with this precipitate from THF solutions containing Tm2+ revealed that, in contrast to 85Sr2+, 109Cd and 65Zn traces cocrystallize with the solid solvate phase. The cocrystallization coefficients D of 109Cd and 65Zn increase with increasing Tm3+/Tm2+ ratio in the solution. The mechanism suggested is that, in the presence of Tm2+, 109Cd2+ and 65Zn2+ 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).