Extraction kinetics of rare-earth elements (La3+, Ce3+, Pr3+, Nd3+, Eu3+) i
n nitric acid, thiocyanate and formate into D2EHPA (bis-2-ethylhexyl phosph
oric 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 trans
fer coefficients remain consistent for the metal ions investigated within a
given aqueous system but are found to be approximately 25% higher in the f
ormate system than in others. An explanation can be given by coupled diffus
ion of cationic and anionic species. (C) 1999 Elsevier Science Ltd. All rig
hts reserved.