Highly selective solvent extraction of uranyl ion using super uranophiles in the presence of methyltrioctylammonium chloride

A highly selective solvent extraction of uranyl ion, UO22+, was carried out by using superuranophiles, i.e., hydroxycalix[n]arene-p-sulfonates, Hj1nn- (n=6, j=2; n=8, j=4), in aqueous solution in the presence of methyltrioctylammonium chloride, MTA+Cl-, in chloroform. In the present extraction, UO22+ in the aqueous phase reacted first selectively and quantitatively with Hj1nn- to form a complex, (UO216H-3)9- or ((UO2)218H-3)11-, respectively. Then, the resultant complexes combined with MTA+ to form hydrophobic and electrically neutral ionic associates, (MTA+)9 (UO216H-3)9- or (MTA+)11 ((UO2)218H-3)11-, and were extracted quantitatively into chloroform. No interference by the coexisting-metal ions was observed. The presence of a large amount of chloride and carbonate ions decreased the extractability of UO22+. The extracted UO22+ was recovered by the stripping method using 2 M sulfuric acid, retaining Hj1nn- in the chloroform phase as a MTA+ associates. The organic phase could be repeatedly used for subsequent extractions. (author)