Membrane assisted transport of thorium (IV) across bulk liquid membrane containing DEHPA as ion carrier: kinetic, mechanism and thermodynamic studies

Abstract

Abstract Extraction and carrier mediated transport of thorium (IV) ions through bulk liquid membrane containing di-2-ethylhexyl phosphoric acid (DEHPA) in kerosene as metal ion carrier. The feed comprised of thorium (IV) ions solutions containing various concentrations of hydrochloric acid, while sulfuric acid solutions of different concentrations are used as a stripping agent. Various parameters about thorium (IV) ion extraction and transport were investigated: the feed solution acidity, initial metal ions aqueous solution concentration, carrier concentration and stripping agent concentration. More than 85% thorium (IV) is recovered in 960 min using 0.2 M DEHPA/kerosene as carrier and 1.5 M H2SO4 as stripping agent from the 0.0001 M HCl solution containing 50 mg L−1 thorium (IV) as feed. Assuming a consecutive, irreversible extraction and back-extraction (stripping) reactions a simple kinetic model was proposed for estimating the reaction rate constant or reaction rate coefficient under the investigated experimental conditions. The activation energy values of extraction and back-extraction reactions were calculated to be 29.94 kJ mol−1 and 20.55 kJ mol−1, respectively, which indicates that the extraction process was controlled by the mixed regime (both kinetic and diffusion), and the back-extraction process was mainly controlled by diffusion process.