CELLULOSE EXCHANGERS WITH TAILOR-MADE CHELATING GROUPS FOR SELECTIVE SEPARATION OF URANIUM

Several tailor-made cellulose exchangers are investigated with respect to their properties (capacities, distribution coefficients for UO22+, 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 len gth, amidoxime/hydroxamic acid groups and amidrazone/hydrazine groups, also linked together by n-alkanes. The anchor groups are fixed by che mical bonds on cellulose, they are flexible and selected for sixfold c oplanar coordination of UO2+. The distribution coefficients are determ ined in simulated sea water at the same initial concentrations of heav y metal ions [1 mg/l of UO22+, Fe3+, Ni2+, Cu2+, Pb2+, (Zn2+), each]. K(d)(UO22+) depends on the steric conditions and on the properties of the donor groups. Under favourable conditions very high values of K(d) (UO22+) are found, up to log K(d)(UO22+) = 5.5 (K(d) in ml/g) and also high selectivities for UO22+. The influences of the donor groups, of the steric conditions and of the competition between formation of chel ates with the anchor groups and formation of the triscarbonato complex [UO2(CO3)3]4- in solution are discussed.