Uranium(VI) separation from aqueous solution by calix[6]arene modified textiles

The separation of uranium(VI) from aqueous solution by textile bound uranophile calix[6]arenes was studied as a function of pH value and uranium concentration in the absence and presence of competing ions by means of batch experiments. Furthermore, the kinetics of the uranium binding was studied as well as the possibility for remobilization of the bound uranium by solutions of various pH values.
The results showed that calixarene modified textiles are suitable for the separation of uranium from aqueous solution at pH values higher than 4. The applicability in the acidic pH range is limited. Maximal 7.6x10-7 mol uranium per 1 g of the calixarene modified textile is bound at pH 5. The influence of competing ions (sodium, potassium, calcium, magnesium, carbonate and sulfate) on the uranium separation at pH 5 is very small. However, at pH 7 in carbonate rich waters calcium ions have a competing effect due to the formation of the Ca2UO2(CO3)3 (aq) complex.
Under environmentally relevant pH conditions (near-neutral pH range) the uranium is strongly bound to the calixarene modified textile and cannot be mobilized. On the other hand, under acidic conditions an almost complete regeneration of the calixarene modified textile is feasible. The regenerated textile filter material can be utilized for further uranium separation cycles.