Abstract
Both 2,6-bis(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine (n-Pr-BTP), and a synergistic mixture of bis(chlorophenyl)dithio-phosphinic acid ((ClPh)2PSSH) and tri-n-octyl phosphine oxide (TOPO) are able to selectively extract actinides(III) over lanthanides(ni) from nitric acid solutions. We performed counter-current extraction tests in hollow fiber modules (HFM) using these extractants. With n-Pr-BTP, up to 99.95% of americium could be separated from the aqueous feed phase. Lan-thanide co-extraction was in the range of 1%. With the synergistic mixture, up to 99.99% of americium were removed, with approx. 30% of lanthanide co-extraction. However, with the latter system, specific flow rates more than five times higher were possible. This is due to different mass transfer kinetics in the two systems: Kinetic investigations with n-Pr-BTP per-formed in a stirred cell showed that the rate of extraction is controlled by a slow chemical reaction. On the other hand, the chemical reaction with (ClPh)2PSSH + TOPO is fast, and the extraction rate is controlled by diffusion.
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