Separation of Americium(III) from lanthanides in a formate buffer solution using purified Cyanex 301 - 5139

Separation studies during the past decades have demonstrated that ligands with 'softer' donor atoms (e.g., N and S, relative to O) are selective for An(III) over Ln(III) in solvent extraction. Among the selective ligands for Ln(III)/An(III) separation, bis(2,4,4-trimethylpentyl) dithio-phosphinic acid, the active component of the commercially available Cyanex 301 reagent, were found to possess exceptionally high selectivity of An(III) over Ln(III). However, the Ln(III)/An(III) separation in this system is only effective under relatively high and narrow pH values (3.5 - 4), thus requiring accurate control of the acidity during the extraction. With respect to this requirement, a series of buffer reagents (carboxylic acid, amino acid, etc.) were employed to stabilize the pH in the aqueous solution. Among the buffers, the ammonium formate/formic solution has shown the best property in stabilizing the required range of pH and meanwhile maintaining a high Ln(III)/An(III) separation factor. Separation of Am²⁴¹ from Lanthanides (Nd, Eu) by purified Cyanex 301 in this system as a function of the total formate concentration and the equilibrated pH have been studied. Results from a 4-stage cross-current extraction testing has demonstrated the efficiency of Am/Eu separation in the formate buffered extraction system. (authors)