ACTINIDE-AMINOPOLYCARBOXYLATE COMPLEXATION THERMODYNAMICS: AMERICIUM, BERKELIUM, CALIFORNIUM, AND EINSTEINIUM by Matthew Urban Copyright by Matthew Urban 2017 All Rights Reserved A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Master of Science (Nuclear Engineering). Golden, Colorado Date _____________________ Signed: _______________________ Matthew Urban Signed: _______________________ Dr. Jenifer C. Shafer Thesis Advisor Signed: _______________________ Dr. Mark Deinert Committee Member Golden, Colorado Date _____________________ Signed: _______________________ Dr. Mark Jensen Program Director Nuclear Science and Engineering Department ii ABSTRACT Previous experiments revealed evidence for modestly selective interactions, encouraged by orbital degeneracy driven covalency, between berkelium and curium using the aromatic aminopolycarboxylate dipicolinic acid. To further probe the ability for the heaviest available actinides to participate in orbital degeneracy driven covalent interactions, solvent extraction competition investigations were completed with the late actinides americium, berkelium, californium, and einsteinium. These studies were completed with aliphatic aminopolycarboxylates (nitrilotriacetic acid, 2-hydroxyethyl ethylenediaminetriacetic acid, trans- 1,2-cyclohexanediaminetetraacetic acid, and diethylenetriaminepentaacetic acid). The stability constants and thermodynamic parameters derived from these studies may provide some indication of covalency in heavy actinide-aliphatic amine complexation chemistry. The stability constants derived for all metal-ligand complexes in this study were compared to lanthanide stability constants of the same aminopolycarboxylates (APCs) in linear free energy relationships to address, in part, whether a difference in selectivity exists between the late actinides and their lanthanide counterparts. Californium and einsteinium displayed a 2% difference in selectivity from europium and gadolinium, respectively, in absolute terms. Little evidence was obtained that shows intra-actinide selectivity between the aliphatic amines and the trivalent actinides. iii TABLE OF CONTENTS ABSTRACT ................................................................................................................................... iii TABLE OF CONTENTS ............................................................................................................... iv LIST OF FIGURES ...................................................................................................................... vii LIST OF TABLES ....................................................................................................................... xiv LIST OF SYMBOLS .................................................................................................................. xxii ACKNOWLEDGEMENTS ....................................................................................................... xxiii Chapter 1 INTRODUCTION .......................................................................................................... 1 1.1 Executive Summary .................................................................................................. 1 1.2 Motivation ................................................................................................................. 2 1.3 Thesis Organization ...................................................................................................... 2 Chapter 2 BACKGROUND ............................................................................................................ 4 2.1 The Nuclear Fuel Cycle ................................................................................................ 4 2.2 Overview of actinide covalency .................................................................................... 9 2.3 Recent findings ........................................................................................................... 13 2.4 Hypothesis................................................................................................................... 15 2.5 Project Specific Reagents ........................................................................................... 16 2.5.1 Nitrilotriacetic acid (NTA) .......................................................................... 16 2.5.2 2-Hydroxyethyl Ethylenediaminetriacetic acid (HEDTA) .......................... 17 2.5.3 Trans-1,2-cyclohexanediaminetetraacetic Acid (CDTA) ............................ 18 2.5.4 Diethylenetriaminepentaacetic acid (DTPA) ............................................... 19 2.5.5 HDEHP Organic Cation Exchange Extractant ............................................ 19 Chapter 3 EXPERIMENTAL CONDITIONS .............................................................................. 21 3.1 Chemicals .................................................................................................................... 21 3.2 Potentiometry .............................................................................................................. 22 3.3 Extraction Studies ....................................................................................................... 22 3.4 APC Distribution Studies ............................................................................................ 25 Chapter 4 RESULTS..................................................................................................................... 28 iv 4.1 Extraction Equilibria ................................................................................................... 28 4.1.1 Extraction Equilibria Results ....................................................................... 29 4.1.2 Extraction equilibria thermodynamics ......................................................... 33 4.1.3 Extraction thermodynamic results ............................................................... 37 4.2 Competition Studies .................................................................................................... 37 4.3 NTA Complexation Studies ........................................................................................ 39 4.3.1 NTA-Am Studies ......................................................................................... 39 4.2.2 Bk-NTA Studies........................................................................................... 41 4.2.3 Californium-NTA Studies ............................................................................ 43 4.2.4 Einsteinium-NTA Studies ............................................................................ 45 4.4 HEDTA Competition Studies ..................................................................................... 47 4.4.1 Americium-HEDTA .................................................................................... 47 4.4.2 Bk-HEDTA .................................................................................................. 49 4.4.3 Cf-HEDTA ................................................................................................... 50 4.4.4 Es-HEDTA ................................................................................................... 51 4.5 CDTA Competition Studies ........................................................................................ 52 4.5.1 Bk-CDTA ..................................................................................................... 52 4.5.2 Cf-CDTA ..................................................................................................... 54 4.5.3 Es-CDTA ..................................................................................................... 55 4.6 DTPA Complexation Studies ...................................................................................... 56 4.6.1 Bk-DTPA ..................................................................................................... 57 4.6.2 Cf-DTPA ...................................................................................................... 59 4.6.3 Es-DTPA ...................................................................................................... 61 Chapter 5 DISCUSSION .............................................................................................................. 63 5.1 NTA ............................................................................................................................ 63 5.2 HEDTA ....................................................................................................................... 66 v 5.3 CDTA .......................................................................................................................... 69 5.4 DTPA .......................................................................................................................... 71 5.5 Comparison to Lanthanides ........................................................................................ 75 Chapter 7 FUTURE WORK ......................................................................................................... 85 REFERENCES ............................................................................................................................. 87 Appendix A INDIVIDUAL VAN’T HOFF PLOTS .................................................................... 90 Appendix B ACID DISSOCIATION CONSTANTS AND STABILITY CONSTANTS ........... 92 Appendix C EXAMPLE STABILITY CONSTANTS