Extraction of rubidium and caesium from strongly alkaline media

Huge amounts of alkaline liquid waste containing a high sodium salt concentration (and in some cases, a lesser potassium salt concentration) are contaminated by (137)caesium. Selective removal of radioactive caesium ions, present in the waste at trace level, requires very selective extractants since the ratio of sodium over caesium exceeds 10(5). As expected, calix[4]arene-crown-6 is satisfactory for the extraction of caesium from liquid waste containing large amounts of sodium. The presence of potassium, which competes more than sodium with caesium, leads to a drastic caesium distribution coefficient decrease as the concentration of this competing cation increases. On the contrary, calix[4]arene and p-tert-butylcalix[4]arene, efficient extractants in high alkalinity media, display an exceptional selectivity for caesium over other alkaline cations, including rubidium. This selectivity of p-tert-butylcalix[4]arene, and to a lesser extent of calix[4]arene, allows caesium to be extracted from alkaline solutions containing large amounts of sodium and potassium.