Rate of Adsorption of Uranium from Seawater with a Calix[6]arene Adsorbent

The rate of complex formation between calix[6]arene-p-hexasulfonate and uranyl ion is studied over a wide range of carbonate ion concentrations. The presence of carbonate ion decreases the complexation rate. The distribution of various uranyl species is calculated from a set of mass balances of participating ions with their stability constants. UO 2 (CO 3 ) 3 4− has the highest concentration, followed by UO 2 (OH) 3 − and UO 2 (CO 3 ) 2 2− . Other uranyl species are negligible. The complexation rate is proportional to the 0.27-1.0 power of the total concentration of uranyl species other than UO 2 (CO 3 ) 3 4− . This implies that the rate-determining step of the complexation is the reaction between calix[6]arene-p-hexasulfonate and UO 2 (OH) 3 − or UO 2 (CO 3 ) 2 2− .