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

Abstract

The rate of complex formation between calix6]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. UO₂(CO₃)₃ ^4? has the highest concentration, followed by UO₂(OH)₃ ^? and UO₂(CO₃)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 UO₂(CO₃)₃ ^4?. This implies that the rate-determining step of the complexation is the reaction between calix6]arene-p-hexasulfonate and UO₂(OH)₃ ^? or UO₂(CO₃)₂ ^2?.