Thermodynamics and kinetics of thorium extraction from sulfuric acid medium by HEH(EHP)

Solvent extraction of Th(IV) using 2-ethylhexyl phosphoric acid mono 2-ethylhexyl ester (HEH(EHP)) in kerosene from sulfuric acid medium was studied by investigating the dependence of thorium extraction on aqueous acidity and HEH(EHP) concentration. The extraction mechanism was also determined by slope analysis. Th(IV) extraction kinetics was investigated using a constant interfacial cell with a laminar flow, and the data were analyzed based on the principle of pseudo first-order reaction. Some parametersʹ effect on the mass transfer, including the effect of temperature, Th(IV) concentration, HEH(EHP) concentration and pH was studied, and the rate equation for thorium extraction was obtained through slope analysis. Based on the high activation energy (Ea = 45.8 kJ mol− 1), the extraction regime was defined to be an interfacial chemical reaction control. In addition, a mass transfer model with a rate-control step was proposed and it was consistent with the experimental results.