Extraction kinetics of rare-earth elements (La3+, Ce3+, Pr3+, Nd3+, Eu3+) in nitric acid, thiocyanate and formate into D2EHPA (bis-2-ethylhexyl phosphoric acid ester, 0.05 kmol m(-3)) is studied in a stirred cell at pH = 2.1. Extraction rate is found to be limited by diffusion. Individual mass transfer coefficients remain consistent for the metal ions investigated within a given aqueous system but are found to be approximately 25% higher in the formate system than in others. An explanation can be given by coupled diffusion of cationic and anionic species.