Peter V. Bonnesen

Computer-Aided Design of a Sulfate-Encapsulating Receptor

Custom built: A promising new approach towards more efficient self-assembled cage receptors through computer-aided design is demonstrated. The resulting M(4)L(6) tetrahedral cage, internally functionalized with accurately positioned urea hydrogen-bonding groups (see structure; yellow: predicted, blue: experimental, space-filling: SO(4)(2-)), proved to be a remarkably strong sulfate receptor in water.

A ROBUST ALKALINE-SIDE CSEX SOLVENT SUITABLE FOR REMOVING CESIUM FROM SAVANNAH RIVER HIGH LEVEL WASTE#

ABSTRACT A robust solvent suitable for extracting cesium from alkaline nitrate media like that of the high-level liquid waste stored at the U.S. Department of Energy Savannah River Site has been developed. The solvent is composed of the cesium extractant calix[4]arene-bis-(tert-octylbenzo-crown-6) (“BOBCalixC6”) at 0.01 M, the modifier l-(2,2,3,3-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol (“Cs-7SBT”) at 0.50 M, trioctylamine (“TOA”) at 0.001 M, and the aliphatic diluent Isopar® L. The solvent holds up exceptionally well under various stresses, such as sustained contact with waste simulant and dilute nitric acid; repeated extraction, scrubbing, and stripping cycles; and excessive loading. The behavior of the solvent in batch-equilibrium flowsheet tests conducted at 15, 25, and 45 °C is presented. Flowsheet calculations show that the Savannah River Site requirements for a decontamination factor of 40,000 and a cesium concentration factor of 12 could be met in a 22-stage bank of 25-cm centrifugal contactors at 25 °C with conservative assumptions regarding hydrodynamics and stage efficiency. Exploiting the temperature dependence of extraction and stripping could reduce the number of stages to 18.

A Striking Effect of Ionic‐Liquid Anions in the Extraction of Sr2+ and Cs+ by Dicyclohexano‐18‐Crown‐6

Abstract The nature of the ionic‐liquid (IL) anion has been found to have a remarkable effect on the solvent extraction of Sr2+ and Cs+ by dicyclohexano‐18‐crown‐6 dissolved in ionic liquids. In particular, the extraction efficiency increases with the hydrophobicity of the IL anion as reflected by the solubility in water of ILs having a common cation. Since a cation‐exchange mechanism is operating in these systems, the influence of the IL anion is in large part attributable to an expected Le Chatelier effect in which a greater aqueous concentration of IL cation, obtained when using an IL anion of lower hydrophobicity, opposes cation exchange. This dependence is opposite to that found for IL cations, indicating a significant advantage of using ILs with hydrophobic anions for cation extraction. Furthermore, the extraction selectivity for Sr2+ over Na+, K+, and Cs+ can be significantly improved through the use of hydrophobic anions for the ILs containing 1‐ethyl‐3‐methylimidazolium or 1‐butyl‐3‐methylimidazolium cations.

SURVEYING THE EXTRACTION OF CESIUM NITRATE BY 1,3-ALTERNATECALIX[4]ARENE CROWN-6 ETHERS IN 1,2-DICHLOROETHANE

ABSTRACT The extraction of cesium nitrate from a mixture of alkali metal nitrates by calix7lsqb;4]arene crown-6 ethers in 1,2-dichloroethane diluent has been surveyed at 25 °C. The results reveal that smaller substituents (but larger than C2,) at the phenolic positions of the calixarene opposite the crown ether increase both the extraction efficiency and the cesium selectivity. Benzo substituents on the crown ether tend to decrease extraction strength while increasing cesium-to-sodium selectivity. Conversely, a cyclohexano group on the crown ether has a negative impact on both extraction strength and selectivity.

Analysis of Equilibria in the Extraction of Cesium Nitrate by Calix[4]arene-bis(t-Octylbenzo- Crown-6) in 1,2-Dichloroethane

The extraction of CsNO3 by the highly lipophilic calixarene-crown ether calix[4]arene-bis(t-octylbenzo-crown-6) (CABOBC6) in 1,2-dichloroethane (1,2-DCE) at 25 °C has been shown to be consistent with the formation of both 1 : 1 and 2 : 1 metal : ligand species. Variation of the aqueous-phase CsNO concentration up to 1.0 M and variation of the organic-phase calixarene concentration up to 0.10∼M was modeled by the program SXLSQI. Formation of the organic-phase species CsBNO3 (B = calixarene) was confirmed as well as the organic-phase dissociation products CsB+ and NO3-. Good evidence for the 2 : 1 metal : ligand organic-phase species Cs2B(NO3)2 was also found, although the dissociation of nitrate from this complex was not observed. Binding of the second Cs+ cation by the ligand is approximately two orders of magnitude weaker than binding of the first Cs+ cation. The logarithm of the apparent partition ratio (log PB) of the calixarene between water and 1,2-DCE was found by 1H-NMR techniques to be > 5.1.

DEVELOPMENT OF A SOLVENT EXTRACTION PROCESS FOR CESIUM REMOVAL FROM SRS TANK WASTE

An alkaline-side solvent extraction process was developed for cesium removal from Savannah River Site (SRS) tank waste. The process was invented at Oak Ridge National Laboratory and developed and tested at Argonne National Laboratory using singlestage and multistage tests in a laboratory-scale centrifugal contactor. The dispersion number, hydraulic performance, stage efficiency, and general operability of the process flowsheet were determined. Based on these tests, further solvent development work was done. The final solvent formulation appears to be an excellent candidate for removing cesium from SRS tank waste.

Development of Effective Solvent Modifiers for the Solvent Extraction of Cesium from Alkaline High‐Level Tank Waste

Abstract A series of novel alkylphenoxy fluorinated alcohols were prepared and investigated for their effectiveness as modifiers in solvents containing calix[4]arene‐bis‐(tert‐octylbenzo)‐crown‐6 for the extraction of cesium from alkaline nitrate media. The structure of the fluorinated portion of the modifier influences the chemical stability, and a modifier that contained a terminal 1,1,2,2‐tetrafluoroethoxy group was found to decompose following long‐term exposure to warm alkaline solutions. However, replacement of the tetrafluoroethoxy group with a 2,2,3,3‐tetrafluoropropoxy group led to a series of modifiers that possessed the alkaline stability required for a solvent extraction process. Within this series of modifiers, the structure of the alkyl substituent (tert‐octyl, tert‐butyl, tert‐amyl, and sec‐butyl) of the alkylphenoxy moiety was found to have a profound impact on the phase behavior of the solvent in liquid–liquid contacting experiments, and hence on the overall suitability of the modifier for a solvent extraction process. The sec‐butyl derivative [1‐(2,2,3,3‐tetrafluoropropoxy)‐3‐(4‐sec‐butylphenoxy)‐2‐propanol] (Cs‐7SB) was found to possess the best overall balance of properties with respect to third phase and coalescence behavior, cleanup following degradation, resistance to solids formation, and cesium distribution behavior. Accordingly, this modifier was selected for use as a component of the solvent employed in the Caustic‐Side Solvent Extraction (CSSX) process designed for the removal of cesium from high‐level nuclear waste (HLW) at the U.S. Department of Energys (DOE) Savannah River Site. In batch equilibrium experiments, this solvent has also been successfully shown to extract cesium from both simulated and actual solutions generated from caustic leaching of HLW tank sludge stored in tank B‐110 at the DOEs Hanford Site.

FUNDAMENTAL INVESTIGATIONS OF SEPARATIONS SCIENCE FOR RADIOACTIVE MATERIALS

ABSTRACT Fundamental investigations of solvent extraction and ion exchange separations of radioactive materials have been conducted within the National Laboratory system of the U. S. Department of Energy (and its predecessor agencies) for the past 50 years. Basic research conducted at Oak Ridge and Argonne National Laboratories has produced both high quality new science and important applications in nuclear technology. The present contribution is an attempt to summarize the most important scientific results arising from this research during the past 10 years, a time of great change in the nuclear separations field, and to suggest possible directions for the next stage of research and development in this field.

Seven-coordinate anion complex with a tren-based urea: Binding discrepancy of hydrogen sulfate in solid and solution states

Structural characterization of a hydrogen sulfate complex with a tren-based urea suggests that the anion is coordinated with six NH···O bonds (d(N···O) = 2.857 (3) to 3.092 (3) Å) and one OH···O bond (d(O···O) = 2.57 (2) Å) from three receptors; however, in solution the anion is bound within the pseudo-cavity of one receptor.

A solution to stripping problems caused by organophilic anion impurities in crown-ether-based solvent extraction systems: a case study of cesium removal from radioactive wastes

Abstract A problem related to stripping efficiency has been identified in the use of crown ether derivatives to extract alkali metal salts, and a simple solution is proposed. Focusing on the specific case of cesium extraction from simulants of alkaline nuclear waste by a calix-crown ether, calix[4]arene-bis( tert -octylbenzo-crown-6) (BOBCalixC6), it has been shown that low concentrations of a common surfactant, dodecylsulfonate, seriously impairs stripping. This surfactant has been identified as a trace component in laboratory simulants and was subsequently studied in experiments in which it was added in controlled amounts. Computer modeling of stripping behavior is consistent with the formation of a 1:1:1 organic-phase complex of the calix-crown with cesium and its nitrate counterion. In the presence of an organophilic surfactant anion, cesium ion can only effectively be stripped from the solvent until its organic-phase concentration becomes equivalent to that of the surfactant anion. Cleanup of nuclear waste requires a high decontamination factor for 137 Cs, and insufficient stripping therefore leads to process failure. This difficulty raises a generic issue for use of crown ethers for waste decontamination or for other hydrometallurgical applications. However, remediation is possible by simply adding an alkylamine to the solvent. The alkylamine in its ammonium form acts as a counterion of the organophilic anion, suppressing the deleterious effects of the organophilic anion and allowing the cesium cation to be stripped efficiently. Trioctylamine (TOA) at a concentration of only 1 mM was found effective at restoring stripping performance while not affecting extraction. Ultimately, this solvent amendment enabled the development of a robust solvent for the Caustic-Side Solvent Extraction (CSSX) process and its successful demonstration on actual nuclear waste.