Synergistic extraction studies on Np(VI) and Pu(VI) have been carried out as a part of the programme on the synergistic extraction
of hexavalent actinides. Extraction of Np(VI) and Pu(VI) were carried out by mixtures of HTTA and TBP in benzene from aqueous
perchlorate and nitrate media. Equilibrium constant values for the various reaction equilibria involved were calculated from
the data obtained by using slope-ratio as well as Job’s method. The extraction of Np(VI) by the synergistic mixture from 1M
nitric acid indicated that the species NpO2 (TTA) (NO3). TBP was not involved in the extraction. The log values of KA, KAB and βAB were −1.5, 2.92 and 4.43, respectively for Np(VI) and −1.63, 2.50 and 4.13 respectively for Pu(VI).