Flotation of uranium from seawater with phosphate esters of C-undecylcalix[4]resorcinarene

Table-type chelating surfactants ([4]ArmX-R(12), mX means the number of phosphates (P), carboxylic acid (Ac), and hydroxamic acid (Hx), respectively) have been derived from the calix[4]resorcinarene bearing tetradodecyl side chains ([4]Ar-R(12)), and applied to a collector of uranium flotation. The surface tension of the aqueous solution was 35 mN m(-1) for [4]Ar5.6P-R(6) (R(n) means the alkyl chain length), 52 mN m(-1) for [4]Ar5.9P-R(12), 42 mN m(-1) for [4]Ar8.0Ac-R(12), and 48 mN m(-1) for [4]Ar5.1Hx-R(12). They formed UO2 complexes and floated the UO22+ from an aqueous solution by air-bubbling. Furthermore, [4]Ar5.9P-R(12) and [4]Ar6.3P-R(12) had competence to float the uranium from seawater. A trace amount of uranium in 450 cm(3) of seawater was floated at 68-94% using 1-10 mg of [4]Ar5.9P-R(12) or [4]Ar6.3P-R(12). On the other hand, [4]Ar5.1Hx-R(12) and [4]AT8.0AC-R(12) brought about lower floatabilities. [4]ArmP-R(12) could be recycled several times by dissolving the scum (uranium complex) in 5 mol dm(-3) H2SO4.