Separation and purification of Rare Earth Elements (REEs) from their mixture are is not easy, because of their similar physico-chemical properties. Therefore, efforts to separate and purify them by the Emulsion Liquid Membrane (ELM) because of their simplicity, effectivity and efficiency. In this study, the emulsion was made by mixing Span-80 as a surfactant, the Tributylphosphate (TBP) or Di-2-Ethylhexylphosphate (D2EHPA) as extractants in N-Hexane, and Nitric Acid as the internal phase, followed by extraction with a mixture of Gd(III) and Sm(III) in nitric acid as an external phase. The emulsion was made using an experimental design with a two-level factorial design method to select parameters that had a significant influence on the response of swelling ratios and creaming number in the separation of Gd(III) from Sm(III). The results of the study showed that the parameters selected were: Internal acidic concentration (0.5 M), surfactant concentration (2.9%), ligand concentration (0.1%), emulsification stirring speed (10000 rpm), external acid concentration (5.8 M), type of ligand (1= ligand code D2EHPA), extraction stirring speed (500 rpm) Furthermore, the data obtained from the research results show that the swelling ratio value was 0,0007 and the creaming rate was -0.0082. The two response values approached the 0 (zero) value, meaning that the resulting liquid emulsion was stable and good for its use in the separation of Gd(III) from Sm(III) by the emulsion liquid membrane method.
