SEPARATION OF ACTINIDES AND LANTHANIDES FROM ACIDIC NUCLEAR WASTES BY SUPPORTED LIQUID MEMBRANES

Abstract

ABSTRACT Supported liquid membranes, SLM, consisting of a solution of 0.25 M octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) and 0.75 μ tributylphosphate (TBP) in decalin absorbed on thin micropocous polypropylene supports, have been studied for their ability to perform selective separations and concentrations of actinide and lanthanide ions from synthetic acidic nuclear wastes. The permeability coefficients of selected actinides (Am, Pu, U, Np) and of some of the other major components of the wastes have been measured using SLMs in flat-sheet and hollow- fiber configurations. The results have shown that with the thin (25 μm) flat-sheet SLMs, using Celgard® 2500 as support, the membrane permeation process is mainly controlled by the rate of diffusion through the aqueous boundary layers. With the thicker (430 μmpar; hollow-fiber SLMs, using Accurel® hollow-fibers as support, the membrane permeation process Is controlled by the rate of diffusion through both the SLM and the aqueous boundary layers. Hollow-fibers SLMs exhibited lower permeability coefficients and longer life-times. The experiments have shown that the actinides can be very efficiently removed from the synthetic waste solutions to the point that the resulting solution could be considered a non-tramsiranic waste (less than 100 mCi/g of disposed form). The work has demonstrated that actinide removal from synthetic Waste solutions is a feasible chemical process at the laboratory scale level. The process is characterized by the typical featirces of SLM's processes, i.e. (a) very small quantities of extractants (b) hlilh feed/strip volume ratios, resulting in a corresponding concentration factor of the actinides, (c) simplicity of operation, which should result in lower capital and operating cost, and (d) negligible solvent enttainment.