Kinetics and mechanism of Re(VII) extraction with mixtures of tri-alkylamine and tri-n-butylphosphate

The extraction kinetics of rhenium(VII) with mixtures of tri-alkylamine (N235, R3N, R = C8 − C10) and tri-n-butylphosphate (TBP) dissolved in heptane has been investigated by constant interfacial cell with laminar flow. The influence of stirring speed, temperature, specific interfacial area, extractant concentration and chloride concentration on the extraction rate has been studied. It is concluded that the extraction of Re(VII) takes place at the liquid–liquid interface, while the extraction regime belongs to kinetic control by chemical reaction. The extraction rate equations and the rate-determining step have been obtained under the experimental conditions, and the extraction rate constant is calculated. The results are also compared with the system with N235 alone as extractant which shows that the Re(VII) extraction rate is enhanced and the activation energy is decreased with the mixtures of N235 and TBP. The separation of Re(VII) from Mo(VI) by kinetics with the mixtures of N235 and TBP is similar to that with N235 alone. Nevertheless, the separation of Re (VII) from Mo(VI) is better under kinetic conditions than under thermodynamic equilibrium conditions.