A new version of the DIAMEX (DIAMide EXtraction) process is reported to separate trivalent Am,Cm (An) and lanthanides (Ln) from a PUREX (Plutonium Uranium Refining by EXtraction by tributyl phosphate) process raffinate at a high aqueous/extractant flow-rate ratio while taking care of prevent third-phase formation. The process has been modeled by a computer program and tested on a 16-stage mixer/settler battery to perform extraction, scrubbing, and stripping to obtain an Am (representing the mixture of Am + Cm) decontamination factor (feed/raffinate) higher than 10(3) and a Mo + Zr fission product content in the product lower than 1 wt% of that of Am. Transient and steady-state concentration profiles of the solutes have been calculated and experimentally determined, and good agreement was generally observed.