On the kinetics of rare-earth extraction into D2EHPA

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.