Studies on the aggregation behavior of mineral acid and Zr(IV) loaded Tris(2-methylbutyl) phosphate and tri-n-alkyl phosphate systems using small angle neutron scattering

Abstract

ABSTRACT The third-phase phenomenon has been observed during the extraction of certain metal ions and mineral acids by 30% (v/v) tri-n-butyl phosphate (TBP) in n-dodecane in the solvent extraction stage of spent nuclear fuel reprocessing. At molecular scale, it has been predicted that the self-organization of the extracted polar species to form reverse micelle-like structure is primarily responsible for third-phase formation. In this regard, the aggregation behavior of solutions of three different trialkyl phosphates in n-alkanes loaded with monoprotic mineral acids (HClO4, HCl and HNO3) as well as tetravalent Th and Zr has been evaluated using Small Angle Neutron Scattering (SANS). The aggregation of TBP has been compared with two of its five carbon analogues i.e. tri-n-amyl phosphate (TAP) and tris(2-methylbutyl) phosphate (T2MBP), which have gained its attention in the course of development of an alternate extractant for the reprocessing process. The effects of trialkyl phosphate structure, diluent chain length and extractant concentration on the aggregation have been emphasized. The contribution of the polar (anionic and cationic component) as well as the apolar part of the reverse micelle toward the phase splitting behavior has been analyzed. The SANS results are in agreement with the earlier reported solvent extraction data.