Analytical separations and speciation for environmental monitoring .

摘要

Partitioning of used nuclear fuel for recycling of fissionable isotopes requires the removal of Cs137 and Sr90 since they produce the bulk of the external radiation hazard and heat generated after the fuel has aged. Liquid-liquid solvent extraction systems have been developed to achieve this extraction. The Caustic-Side Solvent Extraction (CSSX) process was developed to remove cesium from caustic waste and the Fission Product Extraction (FPEX) process was developed to simultaneously remove cesium and strontium from acidic waste. The objective of this research was to determine if these well-characterized systems could be transferred to extractive chromatographic systems to provide analytical tools for environmental sampling. In the CSSX process, BOBCalixC6 is used as the extractant, but is relatively pH-independent, which makes stripping cesium difficult. New extractive chromatographic materials have been prepared using lipophilic calix[4]arene-benzocrown-6 ethers in the 1, 3-alternate conformation functionalized with pendant acidic groups on an inert polymeric substrate. Cesium was strongly retained by the new chromatographic materials in alkaline solutions; at low acid concetrations, the presence of the pendant acid groups reduced the strength of this interaction so that cesium was stripped. These materials exhibited a high selectivity for trace-level cesium over other metals at concentrations up to 0.5M. Column studies showed cesium was retained with 0.01M NaOH and then easily stripped using 0.01M HNO 3. In the FPEX process, BOBCalixC6 and DtBuCH18C6 are used as the extractants; in this research, these same extractants were applied to a chromatographic material. This material exhibited selectivity for cesium and strontium over other metals at concentrations up to 1mM. Column studies showed the material was not suitable for column work, exhibiting poor retention on the column.;The solution speciation of the trivalent lanthanide cations, such as Nd(III), controls their mobility and reactivity. Organic ligands, such as nitriloacetatic acid (NTA), can form complexes with the dissolved cations. The objective of this study was to use electrospray ionization mass spectrometry to characterize the speciation of Nd(III)-NTA solutions. Studies varying the NTA concentration showed an increase in species size as the NTA concentration was increased. The fragmentation potential was also varied which affected the predominant species observed in the mass spectrum. At lower fragmentation potentials, larger molecular species were predominant, whereas, at higher fragmentation potentials, bare neodymium oxide was predominant. Studies were performed to determine which ligands complex with neodymium and these proposed species are presented.