Chemical studies on the extraction of certain elements related to the nuclear fuel cycle

The nuclear fuel cycle comprises a wide range of various processes associated with the production of fuel for nuclear reactors and reprocessing for recycling or direct disposal. Lanthanides and Y represent a considerable portion of fission product in the back end of the nuclear fuel cycle. Separation of individual lanthanides, La - Lu, and their analogues Sc and Y from each other is very difficult and remains a significant technical and economic challenge due to their similarity in physical and chemical properties. The main objective of the work presented in this thesis is to study the extraction and possible separation of different lanthanides by liquid-liquid and solid-liquid extraction techniques. The first part of the thesis, deals with the liquid-liquid extraction behavior of Y(III) and Dy(III) from different dilute acidic media such as HNO₃, HCl and H₂SO₄ acids, by Cyanex 572 as a novel extractant under equilibrium conditions. Characterization of Cy-572 was investigated using different methods such as IR, GC ass, HNMR analysis as well as potentiometric titration. The different parameters affecting the extraction of the above metals from different media were studied. The optimum conditions were evaluated by varying the experimental parameters. The stoichiometry of different extracted species were established. The stripping of the extracted species from loaded Cy-572 in kerosene was also studied. The separation feasibility of different lanthanides plus Y(III) based on the differences in their extracting behaviors was performed. Finally, fractionation studies were developed for the possible separation of heavy lanthanides from light lanthanides leach sulfate solution from Egyptian monazite ore using Cy-572 extractant in kerosene. In the second part, solid-liquid extraction of some heavy lanthanide ions Dy(III), Ho(III), Er(III), Yb(III) as well as its analogue Y(III) from sulfate medium using Cy-572 impregnated on kieselguhr were carried out in both batch and fixed column technique. Characterization of the modified kieselguhr was performed using XRF, SEM, IR techniques as well as thermal analysis. The different parameters affecting the sorption of the relevant metals were studied. The sorption kinetics, isotherm and thermodynamic parameters were estimated and discussed. In addition, Preliminary investigations on the breakthrough curves of the studied lanthanides, in a fixed bed column at room temperature was carried out to assess, the possible use of this system for selective separation of Yb(III) from other lanthanides studied. Further, a comparison between the present work and the previous survey is investigated through the capacity of the impregnated material and the separation factor values towards the studied elements.