UNLV Theses, Dissertations, Professional Papers, and Capstones 8-2011 Equilibrium speciation of select lanthanides in the presence of acidic ligands in homo- and heterogeneous solutions Troy Robinson University of Nevada, Las Vegas Follow this and additional works at: https://digitalscholarship.unlv.edu/thesesdissertations Part of the Analytical Chemistry Commons, Physical Chemistry Commons, and the Radiochemistry Commons Repository Citation Robinson, Troy, "Equilibrium speciation of select lanthanides in the presence of acidic ligands in homo- and heterogeneous solutions" (2011). UNLV Theses, Dissertations, Professional Papers, and Capstones. 1247. http://dx.doi.org/10.34917/2820971 This Dissertation is protected by copyright and/or related rights. It has been brought to you by Digital Scholarship@UNLV with permission from the rights-holder(s). You are free to use this Dissertation in any way that is permitted by the copyright and related rights legislation that applies to your use. 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EQUILIBRIUM SPECIATION OF SELECT LANTHANIDES IN THE PRESENCE OF ACIDIC LIGANDS IN HOMO- AND HETEROGENEOUS SOLUTIONS By Troy Robinson Bachelor of Science Brigham Young University 2005 A dissertation submitted in partial fulfillment of the requirements for the Doctor of Philosophy in Radiochemistry Department of Chemistry College of Science Graduate College University of Nevada, Las Vegas August 2011 Copyright by Troy A Robinson 2011 All Rights Reserved THE GRADUATE COLLEGE We recommend the dissertation prepared under our supervision by Troy Robinson entitled Equilibrium Speciation of Select Lanthanides in the Presence of Acidic Ligands in Homo- and Heterogeneous Solutions be accepted in partial fulfillment of the requirements for the degree of Doctorate of Philosophy in Radiochemistry Department of Chemistry Ken Czerwinski, Committee Chair Sam Bryan, Committee Member Patricia Paviet-Hartman, Committee Member Tatiana Leviskaia, Committee Member Ralf Sudowe, Graduate College Representative Ronald Smith, Ph. D., Vice President for Research and Graduate Studies and Dean of the Graduate College August 2011 ii ABSTRACT Equilibrium Speciation of Select Lanthanides in the Presence of Acidic Ligands in Homo- and Heterogeneous Solutions by Troy Robinson Dr. Kenneth R. Czerwinski, Examination Committee Chair Professor of Chemistry Chair of the Department of Radiochemistry University of Nevada, Las Vegas This dissertation explores lanthanide speciation in liquid solution systems related to separation schemes involving the acidic ligands: bis(2-ethylhexyl) phosphoric acid (HDEHP), lactate, and 8-hydroxyquinoline. Equilibrium speciation of neodymium (Nd3+), sodium (Na+), HDEHP, water, and lactate in the TALSPEAK liquid-liquid extraction system was explored under varied Nd3+ loading of HDEHP in the organic phase and through extraction from aqueous HCl and lactate media. System speciation was probed through vapor pressure osmometry, visible and Fourier Transform Infrared (FTIR) spectroscopy, 22Na and 13C labeled lactate radiotracer distribution measurements, Karl Fischer titrations, and equilibrium pH measurements. Distribution of Nd3+, Na+, lactate, and equilibrium pH were modeled using the SXLSQI software to obtain logKNd and logKNa extraction constants under selected conditions. Results showed that high Nd3+ loading of the HDEHP led to Nd3+ speciation that departs from the ion exchange mechanism and includes formation of highly aggregated, polynuclear [NdLactate(DEHP)2]x; (with x > 1). By substituting lanthanum (La3+) for Nd3+ in this system, NMR scoping experiments using 23Na, 31P nuclei and 13C labeled lactate were performed. Results indicated that this technique is sensitive to changes in system speciation, and that further experiments are warranted. In a homogeneous system representing the TALSPEAK aqueous phase, Lactate protonation behavior at various temperatures was characterized using a combination of iii potentiometric titration and modeling with the Hyperquad computer program. The temperature dependent deprotonation behavior of lactate showed little change with temperature at 2.0 M NaCl ionic strength. Cloud point extraction is a non-traditional separation technique that starts with a homogeneous phase that becomes heterogeneous by the micellization of surfactants through the increase of temperature. To better understand the behavior of europium (Eu3+) and 8- hydroxyquinoline under cloud point extraction conditions, potentiometric and spectrophotometric titrations coupled with modeling with Hyperquad and SQUAD computer programs were performed to assess europium (Eu3+) and 8-hydroxyquinoline speciation. Experiments in both water and a 1wt% Triton X-114/water mixed solvent were compared to understand the effect of Triton X-114 on the system speciation. Results indicated that increased solvation of 8-hydroxyquinoline by the mixed solvent lead to more stable complexes involving 8- hydroxyquinoline than in water, whereas competition between hydroxide and Triton X-114 for Eu3+ led to lower stability hydrolysis complexes in the mixed solvent than in water. Lanthanide speciation is challenging due to the trivalent oxidation state that leads to multiple ligand complexes, including some mixed complexes. The complexity of the system demands well-designed and precise experiments that capture the nuances of the chemistry. This work increased the understanding of lanthanide speciation in the explored systems, but more work is required to produce a comprehensive understanding of the speciation involved. iv ACKNOWLEDGEMENTS I would like to take this opportunity to recognize those who have helped me to this milestone in my development. I would like to thank my wife Linda has been patient and supportive of my long work hours and travel that has taken me away from her and our four children on numerous occasions. I would like to thank the members of my thesis committee: Ken Czerwinski, Tatiana Levitskaia, Sam Bryan and Patricia Paviet-Hartmann for their guidance while writing this dissertation. I would like to thank my thesis advisor, Ken Czerwinski, specifically for all he taught about a career in academia through his example of hard work and dedication. I would also like to thank Tatiana Levitskaia for the individual attention she provided to help improve my analytical chemistry, and attention to details in technical communication. Thanks to Brady Hanson and Sam Bryan who made it possible for me to come to Pacific Northwest National Laboratory and to gain experience performing research in the Radiochemical Processing Laboratory. Thanks to Dean Peterman, Scott Herbst and Terry Todd who gave me the chance to experience Idaho National Laboratory, and who provided valuable experience by entrusting me to work with 14C in their laboratories. v TABLE OF CONTENTS ABSTRACT ........................................................................................................................................ iii ACKNOWLEDGEMENTS .................................................................................................................... v TABLE OF CONTENTS....................................................................................................................... vi LIST OF TABLES ............................................................................................................................... viii LIST OF FIGURES .............................................................................................................................. xii CHAPTER 1 INTRODUCTION ...................................................................................................... 1 1.1 Motivation for Research ...................................................................................................... 1 1.2 Background .......................................................................................................................... 2 1.2.1 Partitioning and Transmutation ................................................................................. 2 1.2.2 Partitioning Schemes Overview ................................................................................. 3 1.2.3 Cloud Point Extraction ............................................................................................. 12 1.2.4 Trivalent Actinide/Lanthanide Separation Principles .............................................. 13 1.3 Summary of Dissertation ................................................................................................... 15 CHAPTER 2 TALSPEAK ORGANIC PHASE SPECIATION UNDER VARIABLE LOADING CONDITIONS: HCL AND LACTATE AQUEOUS MEDIUM STUDIES ......................... 16 2.1 Introduction ....................................................................................................................... 16 2.2 Experimental ..................................................................................................................... 23 2.2.1 Materials .................................................................................................................. 23 2.2.2 Vapor Pressure Osmometry of Aqueous