Abstract: The invention involves a process for separating actinides and lanthanides by liquid-liquid extraction by means of calixarenes. These calixarenes have the formula: with R1 and R2 being alkyl groups or o-nitrophenoxy alkyl groups and R3 and R4 being aryl groups, and they are used in an organic liquid phase containing an organic diluent. The diluent and the calixarene concentration of the organic phase are chosen so as to ensure an enrichment of the organic phase with the actinide(s) and/or lanthanide(s) to be separated from an aqueous acid or saline solution.

Abstract: The invention involves the separation of actinides and lanthanides by membrane transport by means of a calixarene. To this end, a first aqueous solution containing at least one metal from the group of actinides and lanthanides to be separated is placed in the compartment 3 and a second aqueous re-extraction solution such as a 10−2 mol/L solution of HNO3 is placed in the compartment 5. The membrane 6 is a microporous membrane of which the pores are filled with a liquid organic phase (calixarene and diluent) chosen in order to favour membrane transport of the metal(s) to be separated from compartment 3 to compartment 5.