Cellulose exchangers with tailor-made chelating groups for selective separation of uranium

Summary

Several tailor-made cellulose exchangers are investigated with respect to their properties (capacities, distribution coefficients for UO ₂ ²⁺ , Fe³⁺, Ni²⁺, Cu²⁺, Pb²⁺ as function of pH, and half-time of exchange). The chelating anchor groups are: 8-oxa-2,4,12,14-tetraoxopentadecane, malonic acid groups linked together by n-alkanes of various chain length, amidoxime/hydroxamic acid groups and amidrazone/hydrazide groups, also linked together by n-alkanes. The anchor groups are fixed by chemical bonds on cellulose, they are flexible and selected for sixfold coplanar coordination of UO ₂ ²⁺ . The distribution coefficients are determined in simulated sea water at the same initial concentrations of heavy metal ions [1 mg/1 of UO ₂ ²⁺ , Fe³⁺, Ni²⁺, Cu²⁺, Pb²⁺, (Zn²⁺), each]. K_d(UO ₂ ²⁺ ) depends on the steric conditions and on the properties of the donor groups. Under favourable conditions very high values of K_d(UO ₂ ²⁺ ) are found, up to log K_d(UO ₂ ²⁺ )=5.5 (K_d in ml/g) and also high selectivities for UO ₂ ²⁺ . The influences of the donor groups, of the steric conditions and of the competition between formation of chelates with the anchor groups and formation of the triscarbonato complex [UO₂(CO₃)₃]⁴⁻ in solution are discussed.