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 field0.
Original language | English |
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Pages (from-to) | 605-631 |
Number of pages | 27 |
Journal | Solvent Extraction and Ion Exchange |
Volume | 18 |
Issue number | 4 |
DOIs | |
State | Published - 2000 |
Funding
Calixarene Extractant Development Inthe mid-90s, a new class ofcrown ethers exhibiting remarkable cesium extraction strength and selectivity was reported by French and Italian workers.(37) First prepared by groups at Parma and Strasbourg, cesium extraction and transport by I,3-aft calix[4]arene crown-S ethers were investigated by Dozol and coworkers at Cadarache.(38) The observed cesium/sodium selectivities were greater than 10', and significantly stronger cesium binding was obtained than had been previously reported for crown ethers. In a project funded by the EM-50 branch ofDOE, the ORNL group synthesized calix[4]arene-biS-l-octylbenzo-crown-6 (Figure 8) to obtain the necessary solubility in aliphatic hydrocarbons preferred for a cesium solvent-extraction process.(31 ,39,40,41,42) Unfortunately, the low polarity ofthe aliphatic diluent resulted in unacceptably low distribution of cesium to the organic phase. Work performed under the auspicesof the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Divisionof Chemical Sciencesunder contracts W-3I-J09-ENG·38 withArgonne National Laboratory and DE-AC05-000R22725 with Oak Ridge National Laboratory, managed and operated by UT-Battelle, LLC. shortcomingofPUREX byextracting trio, (C,Hl1(p"CH,/C"N(C,H,), tetra-, and hexavalent actinide ions into a . 1 process solvent. The CMPO Figure I. Octyl(phenyl)-N,N-diisobutyl-SIng e carbamoylmethylphosphine oxide extractant was designed, synthesized and characterized in basic research funded by DOEIBES and subsequently tested under benchscale process conditions under the auspices of other DOE funding agencies supporting application development. This class of extractants continues to be a subject ofinvestigations around the world. During the design and characterization ofthe CMPO reagent and the TRUEX process, the need was recognized for a water-soluble complexing agent that would strongly bind actinide ions and quantitatively remove them from the TRUEX Process Solvent. Because common stripping agents like ethylenediamine-N,N,N',N'-tetraacetic acid (EDTA) are known to have a long environmental half-life and to promote mobility of radionuclides in soils, it was decided that these new stripping agents should be readily decomposable. Early studies established that substituted methanediphosphonic acids are extremely effective complexants for polyvalent actinide ions, even in solutions of high to moderate acidity. Subsequent research at ANL established that certain derivatives of methane diphosphonic acid now referred to as thermally unstable complex ants (TUCS) are readily mineralized to H,O, CO" and H,PO" either spontaneously or upon treatment with mild oxidants.(4) Aspects of the basic coordination chemistry of lanthanide and actinide complexes with about 15 different derivatives ofmethanediphosphonic acid have been investigated.(5) One derivative of methanediphosphonic acid proved particularly versatile. VinylideneI, I-diphosphonic acid (VDPA) was prepared initially using a pyrolytic dehydration of the tetra-sodium salt of I-hydroxyethane-l, l-diphosphonic acid (HEDPA). Somewhat surprisingly, VDPA formed the most soluble lanthanide and actinide complexes. The double bond on the vinylidene backbone has allowed the development and testing ofa variety of2substituted derivatives. Further investigations, conducted in collaboration with Professor Spiro Alexandratos at the University of Tennessee and supported by the DOE office of Advanced Energy Projects, led to the preparation of'Diphonix" cation exchange resin (Figure 2), which features a geminal diphosphonic acid chelating group as the primary metal ion recognition site.(6)