Anal. Chem. 1995,67,3903-3910
Automated Bn=LineExtraction of Uranium(V1) from Raffinate Streams with On=LineDetection by Cathodic Stripping Voltammetry Johannes T. van Elteren,t Constant M. G. van den -,*it
Hao Zhang,tit Trevor D. Martin,* and
Eric P. Achterbergt OceanographyLaboratories, University of Liverpool, P.O. Box 147, Liverpool L69 3BX U.K.,and Analybcal Services Technical Department B229, Chemical Analysis, BNFL, Sellafield Seascale, Cumbria CA 20 1PG, U.K.
An automated method for on-sitemonitoring of uranium(VI) in raftbate streams originating h m nuclear fuel reprocessing plants is described. An in-line stripping procedure (based on liquid/liquid extraction) was developed to extract U(VI) h m this stream,a solvent mixture of 20%tributyl phosphate and nitric acid in kerosene, into an aqueous sodium sulfate solution. Degradation products in the solvent mixture, especially dibutyl phosphate, give rise to very strong complexes and are responsible for moderate but constant U(VI) recoveries (-50%). Optimal conditions for in-line stripping comprise a mixing ratio of extractant (0.5 M sodium sulfate in water)/solvent mixture of -3 and a pumping rate of -0.4 mL min-' of the solvent mixture. The determination of U(VI) was by preceded on-line cathodic strippingvoltammmetty by adsorptive collection of the U(VI) as an oxine complex onto a hanging mercury drop electrode. Quantities of 1-2 mL of the aqueous extract were pumped into the voltammetric cell and diluted (1/5 to 1/10) with a background electrolyte containing 0.1 M PIPES buffer, 2x M oxine, M EDTA, and 0.2 M hydrazine hydrate @H 9.0). The CSV peak for U(VI) was obtained at -0.68 Vwith a detection limit of 20 nM in the raftinate stream using an adsorption lime of 120-s. Both the inline stripping procedure and the on-line measurement were fully automated, with a relative standard deviation in the measurements of 99.5% of the U O is transferred to the solvent as a result of complexation by TBP. A degraded &ate was obtained from BNFL (British Nuclear Fuels plc) to test the system. This simulated sample contained kerosene (80%),TBP (-20%), nitric acid (0.2-0.3 M), RNOz (0.9%), RNO3 (0.5%),RlRzCO (0.5%),RCOOH (
