We report molecular dynamics studies on the interfacial behavior of species involved in the assisted liquid-liquid extraction of cesium and uranyl cations. The distribution of uncomplexed Cs+Pic- and UO2(NO3)2 salts is first described at the water / chloroform interface. This is followed by simulations of monolayers of calix[4]arene-crown6 Cs+Pic- complexes at the interface, where they are found to remain adsorbed, contrary to expectations from extraction experiments. The question of synergistic effects is addressed by simulating these calixarenes at a TBP saturated interface (TBP = tributylphosphate). Finally, in relation with the extraction of uranyl by TBP, we report a computer demixing experiment of a "perfectly mixed" ternary water / chloroform / TBP mixture containing 5 UO2(NO3)2 molecules. The phase separation is found to be rapid, leading to the formation of a TBP layer between the aqueous and organic phases and to spontaneous complexation of the uranyl salts by TBP. The complexes formed are not extracted to chloroform, but remain close to the water / organic phase boundary. The simulations reveal the importance of interfacial phenomena in the ion extraction and recognition processes.