Kinetics of Cerium(IV) Extraction with DEHEHP From HNO3‐HF Medium Using a Constant Interfacial Cell with Laminar Flow

Abstract

Studies of the extraction kinetics of cerium(IV) into n‐heptane solutions of di(2‐ethylhexyl)‐2‐ethylhexyl phosphonate DEHEHP from HNO3‐HF solutions have been carried out using a constant interfacial cell with laminar flow. The experimental hydrodynamic conditions were chosen so that the contribution of diffusion to the measured rate of reaction was minimized. The data were analyzed in terms of pseudo‐first order constants. The effects of the stirring rate, specific interfacial area, and temperature on the extraction rate showed that the most probable reaction zone is in the aqueous homogeneous phase. The results were compared with those of the system without HF. It was concluded that the presence of HF decreases the extraction rate of cerium. The addition of HF increases the activation energy for the forward reaction from 21.2 to 55.3 kJ/mol and for the reverse process from 57.9 to 79.0 kJ/mol. According to the experimental data correlated as a function of the concentration of the relevant species involved in the extraction reaction, the corresponding rate equation was deduced as follows: The kinetic mechanism of the extraction process was proposed taking an aqueous chemical reaction as the rate‐determining step of the overall reaction.