Extraction of europium(III) into W/O microemulsion containing aerosol OT and a bulky diamide. I. Cooperative effect

The extraction of Eu(III) from aqueous HNO3 solution into a water-in-oil (W/O) microemulsion occurring in hexane was studied. Aerosol OT (AOT(-)) was used as an anionic surfactant, and a bulky diamide (DA), N,N'-dioctyl-N,N'-dimethyl-2-(3'-oxapentadecyl)propane-1,3-diamide, was employed as an electrically neutral extractant. The combination of AOT(-) and the DA shows a very strong cooperative effect on the metal extraction. The microemulsion containing AOT(-) alone in hexane, equilibrated with the acidic solution, is unstable. However, in the presence of the electrically neutral extractant acting as a masking ligand to H+, the microemulsion in the hexane phase is dramatically stabilized, which enhances the distribution of Eu(III) to the organic phase. The distribution of the metal in the micellar extraction system is also greatly affected by the concentration of an electrolyte, such as HNO3 or NaNO3, playing two important roles, i.e., the formation of the microemulsion, promoting the metal extraction, and the ion-exchange of the metal ion for the cation yielded from the electrolyte, contrarily, suppressing the metal extraction.