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 137Cs, 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.
| Original language | English |
|---|---|
| Pages (from-to) | 9-19 |
| Number of pages | 11 |
| Journal | Hydrometallurgy |
| Volume | 72 |
| Issue number | 1-2 |
| DOIs | |
| State | Published - Feb 2004 |
Funding
We want to thank Haiteng Deng and Gary J. Van Berkel in the Organic and Biological Mass Spectrometry Group at ORNL for the access to the ES-MS instrument and for experimental assistance. We also thank Tatiana G. Levitskaia and Jeffrey C. Bryan for internal review of the manuscript. A sample of one batch of simulated waste was kindly supplied by Ralph A. Leonard and co-workers at Argonne National Laboratory. This research was sponsored by the Efficient Separations and Processing (ESP) Crosscutting Program, Office of Science and Technology, Office of Environmental Management, USDOE under contract number DE-AC05-00OR22725 with ORNL, managed and operated by UT-Battelle, LLC. Additional funding was also provided by the Westinghouse Savannah River Company for the Office of Project Completion, Office of Environmental Management, USDOE.
| Funders | Funder number |
|---|---|
| Office of Project Completion | |
| Office of Science and Technology | |
| U.S. Department of Energy | DE-AC05-00OR22725 |
| Office of Environmental Management | |
| Oak Ridge National Laboratory |
Keywords
- Crown ether
- Organophilic anion impurities
- Stripping