Immobilisation of Caesium from Crystalline Silicotitanate by Hot Isostatic Pressing by Tzu-Yu Chen Supervisor: Dr Joseph A. Hriljac A thesis submitted to The University of Birmingham for the degree of Doctor of Philosophy The School of Chemistry College of Engineering and Physical Sciences University of Birmingham Oct 2012 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder. Abstract Abstract The main aim of this project was to develop a durable ceramic wasteform by HIPing Cs- exchanged crystalline silicotitanate (CST) used for nuclear waste clean-up. The sodium form (Na-CST) and niobium substituted sodium form (Na-Nb/CST) CST were hydrothermally synthesised and characterised. The synthesised CSTs and a commercial CST containing material, IONSIV®, were subjected to ion exchange studies and then the crystal phases present after HIPing were investigated. Cs-IONSIV® was thermally decomposed and converted to two major Cs-containing phases, Cs2TiNb6O18 and Cs2ZrSi6O15, and a series of other phases. Additionally the effect of metal addition on phase formation under HIP conditions was explored. The microstructure and phase assemblage of HIPed Cs-IONSIV® samples as a function of Cs content were examined using XRD, XRF, SEM and TEM/EDX. To understand the Cs bonding environment in these Cs-containing phases, structural characterisation was undertaken using Rietveld analysis of synchrotron X-ray powder diffraction data and neutron diffraction data. The potential of these phases for hosting Cs+ and its decay product Ba2+ was also studied. This thesis is also concerned with determining the aqueous durability of these HIPed samples by carrying out MCC-1 and PCT-B leach tests. These show very low Cs leach rates and the promise of safe long-term immobilisation of Cs from CSTs as well as suggesting these phases are more leach resistant than hollandite - the material targeted for Cs sequestration in Synroc. I Acknowledgements Acknowledgements First and foremost I would like to acknowledge my supervisor Dr. Joe Hriljac for his invaluable support, guidance and patience throughout this PhD. I would also like to thank Prof. Neil Hyatt and Dr. Ewan Maddrell for their advice and encouragement. This thesis would have never been possible without their input. The additional sponsorship from School of Chemistry, University of Birmingham and NNL was greatly appreciated. Thanks go to the members of the 5th floor Chemistry, past and present, for their help and always making it an enjoyable place to work. A massive thank you must be expressed to Ben, Cathryn, Ivan, Yasmin and Ying, for those days panicking together and supporting each other, Tom M and Alex for helping me fit in and improving my English (in a slightly painful way), Victoria and Tom C for sharing their precious synchrotron beam time with me, Dr. Jackie Deans and Annabelle for the technical support and the big smiles and my friends Yina and Su, from Mat & Met, for the help and company since the very beginning of our PhDs. Special mention to the following people who have helped with the acquisition of results included in this thesis. Mr. Mike Glynn, Univ. Birmingham, for running the HIP and being an entertaining and supportive friend. Dr. Martin Stennett and Dr. Amy Gandy, Univ. Sheffield, for their help with TEM microstructure analyses, Mr. Paul Stanley and Dr. Ming Chu, Univ. Birmingham, for the SEM and TEM support, Mr. Steve Baker, Univ. Birmingham, for the ICP analyses and Dr. Ron Smith, ISIS, for the neutron diffraction data collection. Most of all I would like to thank my parents and my beloved family for their unconditional support and encouragement. Without them I would never been able to gain this incredible experience of studying abroad, making lifelong friends and having the chance to make them proud of me. Thank you! II Abbreviations Abbreviations CST Crystalline Silicotitanate Na-CST Sodium Crystalline Silicotitanate, Na2Ti2O3SiO4∙2H2O Na-Nb/CST Niobium Substituted Crystalline Silicotitanate PXRD Powder X-ray Diffraction XRD X-ray Diffraction GSAS General Structural Analysis System BVS Bond Valence Sum SEM Scanning Electron Microscopy EDX Electron Dispersive X-ray TEM Transmission Electron Microscopy XRF X-ray Fluorescence TGA Thermogravimetric Analysis DTA Differential Thermal Analysis MS Mass Spectrum HIP Hot Isostatic Pressing ASTM American Society for Testing and Materials MCC Materials Characterisation Centre PCT Product Consistency Test III Table of Contents Table of Contents Chapter 1 Introduction ........................................................................................ 1 1.1 Background ....................................................................................................................... 1 1.2 Inorganic Ion Exchangers ................................................................................................. 3 1.3 General Immobilisation Options ...................................................................................... 7 1.3.1 Glass Wasteforms .................................................................................................... 10 1.3.2 Ceramic Wasteforms ............................................................................................... 13 1.3.3 Glass-ceramic Composite Wasteforms .................................................................... 18 1.3.4 Cements ................................................................................................................... 20 1.3.5 Other Wasteforms .................................................................................................... 21 1.4 Processing of Wasteforms .............................................................................................. 21 1.4.1 Melting and Vitrification ......................................................................................... 21 1.4.2 Powder Processing and Sintering ............................................................................ 22 1.4.3 Sol-gel Processing ................................................................................................... 22 1.4.4 Microwave Processing ............................................................................................. 22 1.4.5 Hot Pressing ............................................................................................................. 23 1.5 Scope of the Study .......................................................................................................... 23 Chapter 2 Experimental ................................................................................... 25 2.1 Synthesis ......................................................................................................................... 25 2.1.1 Hydrothermal Synthesis .......................................................................................... 25 2.1.2 Solid State Reactions ............................................................................................... 26 2.1.3 Sol-gel Method ........................................................................................................ 27 2.2 Crystallography and Diffraction ..................................................................................... 28 2.2.1 Fundamentals of Crystallography ............................................................................ 28 2.2.2 Diffraction ............................................................................................................... 30 2.3 X-ray Diffraction ............................................................................................................ 31 Table of Contents 2.3.1 Generation of the X-rays ......................................................................................... 31 2.3.2 Powder Diffraction .................................................................................................. 34 2.3.3 Laboratory Diffractometers ..................................................................................... 36 2.3.4 Synchrotron X-ray Diffraction ................................................................................ 37 2.4 Neutron Diffraction ........................................................................................................ 38 2.5 Rietveld Refinement ....................................................................................................... 41 2.6 Bond Valence Sum ......................................................................................................... 44 2.7 Electron Microscopy....................................................................................................... 45 2.7.1 SEM/EDX ................................................................................................................ 46 2.7.2 TEM ......................................................................................................................... 50 2.8 X-ray Fluorescence Spectroscopy (XRF) ......................................................................