Developing and testing an alkaline-side solvent extraction process for technetium separation from tank waste

Engineering development and testing of the SRTALK solvent extraction proces s are discussed in this paper. This process provides a way to carry out alk aline-side removal and recovery of technetium in the form of pertechnetate anion from nuclear waste tanks within the DOE complex. The SRTALK extractan t consists of a crown ether, bis-4,4'(5')[(tert-butyl)cyclohexano]-18-crown -6, in a modifier, tributyl phosphate, and a diluent, Isopar(R)L. The SRTAL K flowsheet given here separates technetium from the waste and concentrates it by a factor of ten to minimize the load on the downstream evaporator fo r the technetium effluent. In this work, we initially generated and correla ted the technetium extraction data, measured the dispersion number for vari ous processing conditions, and determined hydraulic performance in a single -stage 2-cm centrifugal contactor. Then we used extraction-factor analysis, single-stage contactor tests, and stage-to-stage process calculations to d evelop a SRTALK flowsheet. Key features of the flowsheet are (1) a low orga nic-to-aqueous (O/A) flow ratio in the extraction section and a high O/A fl ow ratio in the strip section to concentrate the technetium and (2) the use of a scrub section to reduce the salt load in the concentrated technetium effluent. Finally, the SRTALK process was evaluated in a multistage test us ing a synthetic tank waste. This test was very successful. Initial batch te sts with actual waste from the Hanford nuclear waste tanks show the same te chnetium extcactability as determined with the synthetic waste feed. Theref ore, technetinm removal From actual tank wastes should also work well using the SRTALK process.