GADOLINIUM SEPARATION FROM HNO3 ACIDIC STREAMS OF THE NUCLEAR-FUEL REPROCESSING BY A NEW CONTINUOUS-FLOW EXTRACTION METHOD

A method for the continuous transfer of gadolinium from one aqueous phase into another was developed, based on the extraction from a light 0.5 M HNO3 phase into a heavier organic phase consisting of 63 Vol% HDEHP (Bis-(2-ethylhexyl)-hydrogenphosphate) in CHCl3 and the subsequent stripping of the ion into a heavy 4 M H2SO4 solution. During operation the two aqueous phases are mobile, while the organic phase is the stationary one. It was shown that an equilibrium between extraction and stripping builds up that can be maintained for hours. The gadolinium separation achieved by this method allows not only the transfer of this ion into a pure aqueous medium with only a short delay between extraction and stripping, but also its continuous enrichment in the stripping phase. Thus, the apparatus is an ideal tool for combination with analytical flow methods that need purification steps prior to analysis, like continuous fluorimetric Gd determination in nitric acid streams. The best working conditions for the system were determined by examining the influences of the mobile phases flow rates, the ratios of flow rates between the two aqueous streams, and the stirring efficiency.