Developing and Testing an Alkaline-Side Solvent Extraction Process for Technetium Separation From Tank Waste

Abstract

Laboratory -Engineering development and testing of the SRT~K solvent extraction process are discussed in this paper. This process provides a way to carry out alkaline-side removal and recovery of technetium in the form of pertechnetate anion from nuclear waste tanks within the DOE complex. The SRTALK extractant consists of a crown ether, bis-4,4'(5')[(tert-butyl)cyclohexano] -18-crown-6, in a modifier, tributyl phosphate, and a diluent, Isopar%. The SRTALK flowsheet given here separates technetium ilom the waste and concentrates it by a factor often to minimize the load on the downstream evaporator for the ., technetium effluent. In this work, we initially generated and correlated the technetium extraction data, measured the dispersion number for various 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 develop a SRTALK flowsheet. Key features of the, flowsheet are (1) a low O%afic-to-aqueous

Anion Separation with Metal–Organic Frameworks

“…This bias has been used to advantage to extract sodium pertechnetate from nuclear waste (high in nitrate), for example. [31,32] It should be pointed out that the actual coordination of the anion to Lewis acid centers in solution in most cases is not confirmed, and it is possible that the anion interacts through a mediating water molecule or outer-sphere ionpairing.…”

Incorporating Size Selectivity into Synergistic Solvent Extraction: A Review of Crown Ether-Containing Systems

“…Partitioning of Tc from an aqueous phase initially containing KNO 3 and NaBH 4 into benzene solutions of HTTA and 18C6 or DB18C6 is reported to undergo synergistic enhancement . Significantly more experiments are required to adequately characterize such a complicated system, however, because macroconcentrations of K(I) may compete with the reduced Tc for complexation by the crown ether, extraction of [M(CE)][TcO 4 ] is well-known, , and the reduction of Tc(VII) by BH 4 - is not well characterized in this system (e.g., the extraction kinetics for [K(DB18C6)][TcO 4 ] may be faster than the Tc(VII) reduction kinetics).…”

Development of Process Chemistry for the Removal of Cesium from Acidic Nuclear Waste by Calix[4]arene-crown-6 Ethers

“…For development of an actual engineering flowsheet, the distribution ratios would be used to calculate and optimize countercurrent multi-stage contacting performance to meet explicit design goals regarding decontamination and concentration factors (23). Finally, the Cs selectivity over selected elements Al, B, Fe(III), Hg(II), K, and Na in the SBW simulant was measured using both the Cs-3BOO/150L and Cs-3BOO/150LT solvents, to discern if the addition of TO A would negatively impact the selectivity performance of the solvent.…”

“…With respect to good engineering, the use of centrifugal contacting equipment allows rapid turnover of the solvent, minimal solvent inventory, and because of the short contact times, minimal exposure of the solvent to high radiation fields, thus decreasing losses of the (calixarene-crown ether) extractant by radiolytic degradation (21)(22)(23). Solvent and extractant losses due to entrainment are also minimized due to the forces developed in centrifugal contactors that separate the solvent and aqueous phases.…”

“…Solvent and extractant losses due to entrainment are also minimized due to the forces developed in centrifugal contactors that separate the solvent and aqueous phases. Rapid turnover of the solvent means the most efficient use of the solvent possible, making it feasible to reduce the solvent inventory to just a few hundred gallons for a waste throughput equivalent to that of a full-scale plant capable of processing the 230,000 kL of alkaline radioactive waste stored at DOE's Hanford Site (23).…”