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

Abstract

A solvent suitable for extracting cesium from acidic nitrate media, such as that stored at the U.S. Department of Energy's Idaho National Engineering and Environmental Laboratory (INEEL), has been developed. The solvent possesses good chemical stability, displays excellent cesium selectivity, and provides good extraction and stripping performance with satisfactory phase-coalescence behavior. The calix[4]arene-crown-6 ether used in this solvent (1,3-alt-bis-n-octyloxycalix[4]arene-benzo-crown-6) was selected from a series of mono-and bis-crown-6 derivatives of 1,3-alternate calix [4]arenes that were shown to possess good stability to a simulant of INEEL's Sodium Bearing Waste (SBW). Calixarene -benzo crown ethers possessing an alkyl substituent at the 4-position of the benzocrown, such as calix[4]arene-bis-tert-octylbenzo -crown-6, were shown to be much more susceptible to nitration by the SBW simulant or by 4 M nitric acid than calixarene-benzo crown ethers without the alkyl substituent. The cesium distribution behavior for a solvent comprised of l,3-alt-bis-n-octyloxy -calix[4]arene-benzo-crown-6 at 0.01 M in an aliphatic diluent modified with a fluorine-containing alcohol was shown to be stable over the course of a 60 day continuous contact with the SBW simulant at 25 °C.Toward process development, cesium distribution ratios on extraction (SBW simulant), scrubbing (50 mM nitric acid), and stripping (1 mM nitric acid) operations demonstrated a functional solvent cycle using a solvent of this composition augmented by 0.001 M trioctylamine (TOA). Without this lipophilic amine, stripping is inefficient. The presence of TOA in the solvent had no adverse effect on the Cs distribution behavior during extraction and scrubbing operations, nor did TOA negatively impact the Cs/Na and Cs/K selectivity ratios.

High‐performance liquid chromatography with electrospray ionisation mass spectrometry and diode array detection in the identification and quantification of the degradation products of calix[4]arene crown‐6 under radiolysis

“…As a consequence of the high degree of degradation observed in dodecane, the impact of nitric acid was evaluated only in NPOE solvent. In the presence of 3 M HNO 3 , the surviving amount of (octMC6-H) decreased (27% more loss) 16,18 and these losses probably correspond to the production of the nitro compounds. For this purpose, octMC6-NO 2 and octMC6-(NO 2 ) 2 were determined by external standard calibration by measuring the areas of the LC peaks vs. concentration at their maximum wavelengths.…”

“…14,15 Extensive experiments in the nuclear industry with solvent systems indicate that the degradation of solvent due to exposure to radiolysis, and to a lesser extent hydrolysis, can significantly degrade its performance. Therefore, before developing an extraction process, 16 the radiolytic stability of the system and the characterisation of the degradation products must be investigated. The stability of some calixarene molecules towards nitric acid media and/or radiolysis has already been reported.…”

Membership Rules for a Molecular Box: The Admission Process and Protection Provided to Guest Molecules

“…[1] Molecular cages based on transition-metal vertices often easily self-assemble, and those with inorganic frameworks are of special interest because their rigidity, uncommon in organic ligands, [2][3][4][5] could give rise to high selectivity with respect to guest size.Prussian Blue (PB) and its variants [6][7][8] are insoluble cyanometallate polymers consisting of boxlike subunits that exhibit ion-exchange behavior. We and others have previously described molecular PB analogues with encapsulated cations.…”

Cesium and Strontium Separation Technologies Literature Review

“…Oak Ridge National Laboratory researchers also investigated various calix [4]arene-crown ethers for potential use on INEEL acidic tank waste [89]. This work demonstrated that these extractants are highly effective at removing cesium from acidic media.…”