(477g) Microflow Visualization of Tri-n-Butyl-Phosphate/Dodecane and Nitric Acid in a Centrifugal Contactor

Authors: 
de Almeida, V. F., University of Massachusetts Lowell
Birdwell, J. F. Jr., Oak Ridge National Laboratory
DePaoli, D. W., Oak Ridge National Laboratory
Tsouris, C., Oak Ridge National Laboratory
Despite the common use of centrifugal contactors in nuclear solvent
extraction applications, much is unknown about the underlying microflow
structure. This lack of knowledge hampers the development of a modern continuum
theory able to predict mixing and transport phenomena for solvent extraction
processes. The ability to observe the micromixing flow and distinguish the
motion and configuration of the phases involved is of great importance
theoretically and practically. To that end, we report on
direct, high-speed visualization of the microflow structure for the
tri-n-butyl-phosphate (TBP)/dodecane/nitric acid system.
Further insight is obtained by simultaneous measurement
of the electrical resistance of the phase mixture to support visual
observations.
This work sheds light on a fluid microflow region at the foot of the mixing
zone of the contactor resolving the microsecond/micrometer motion of the
continuous and dispersed phases.
The system in this study is the most prevalent solvent extraction combination
used in the nuclear reprocessing industry to extract metal ions from spent
nuclear fuel from a nitric acid aqueous solution into an organic mixture of
TBP and dodecane. The purpose of this work is to describe salient features
of the behavior of this system, heretofore unknown, to guide the
development of a predictive modeling and simulation approach.

This work also offers unique guidance and insights for continuum-based modeling
of the multiphase mixture mechanics. In particular what aspects of a mixing
theory may provide qualitative and/or quantitative predictions of the rich
phenomena reported here. No multiphase continuum mixture theory is generic enough
for all flows;
therefore, this work is fundamental in guiding the future development of a
predictive theory, modeling and simulation effort at the continuum level.
In fact, the original motivation for this work was to provide
experimental information for building an appropriate mixing theory for the
system at hand. Finally, advances in rigorous modeling of this
system will likely provide the basis for other similar multiphase,
multicomponent fluid transport used in nuclear recycling processes.