The nucleation, growth kinetics and mechanism of sulfate scale minerals in the presence and absence of additives as inhibitors Taher Rabizadeh Submitted in accordance with the requirements for the degree of Doctor of Philosophy The University of Leeds School of Earth and Environment November 2016 i Declaration The candidate confirms that the work submitted is his own, except where work which has formed part of jointly-authored publications has been included. The contribution of the candidate and the other authors to this work has been explicitly indicated below. The candidate confirms that appropriate credit has been given within the thesis where reference has been made to the work of others. Chapter 4 has been published as: Rabizadeh, T., Peacock, C. L. and Benning, L. G., 2014. Carboxylic acids: effective inhibitors for calcium sulfate precipitation?, Mineralogical Magazine, 78, 1465–1472. The experiments, analyses, data processing, interpretation and preparation of the manuscript were conducted by the candidate. All co-authors contributed to data interpretation and manuscript preparation. Chapter 5 has been published as: Rabizadeh, T., Stawski, T. M., Morgan D. J., Peacock, C. L. and Benning, L. G., The effects of inorganic additives on the nucleation and growth kinetics of calcium sulfate dihydrate crystals, Crystal Growth & Design, 17, 582-589. The candidate performed the experiments, analyses (except ICP-MS / OES and XPS measurements), data processing (except XPS measurements), interpretation (except XPS measurements) and preparation of the manuscript. XPS analyses, data processing and interpretation were discussed in depth with co-author David J. Morgan at Cardiff University. All co-authors contributed to data interpretation and manuscript preparation. ii Chapter 6 is in preparation for submission to the Journal of Crystal Growth as: Rabizadeh, T., Morgan D. J., Peacock, C. L. and Benning, L. G. Comparative performance of biodegradable vs. poly(acrylic acid) antiscalants on calcium sulfate dihydrate crystallisation. The candidate performed all experiments, analyses, data processing, interpretation and preparation of the manuscript. XPS analyses were performed at Cardiff University together with David J. Morgan. All co-authors contributed to data interpretation and manuscript preparation. Chapter 7 is in preparation for submission to Langmuir as: Rabizadeh, T., Morgan D. J., Peacock, C. L. and Benning, L. G., Investigating the effects of phosphonate inhibitors on the nucleation and growth kinetics of calcium sulfate dihydrate crystals. The candidate performed the experiments, analyses (except ICP-OES and XPS measurements), data processing, interpretation and preparation of the manuscript. XPS analyses were performed at Cardiff University together with David J. Morgan. All co-authors contributed to data interpretation and manuscript preparation. The right of Taher Rabizadeh to be identified as author of this work has been asserted by him in accordance with the Copyright, Designs and Patents Act 1988. This copy has been supplied on the understanding that it is copyright material and that no quotation from the thesis may be published without proper acknowledgement. © 2016 The University of Leeds and Taher Rabizadeh iii Dedication I dedicate this work to my parents for raising me to be the person I am today, and my wife, Azam, who encouraged and supported me in this work from the beginning. I here extend my dedication to my brother as well as my parents-in-law. iv Acknowledgements I would like to take this opportunity to appreciate some people without whom it would not have been possible to do this work. I would like to express my sincere gratitude to my supervisor, Prof. Liane G. Benning for being supportive, patient, for encouraging me during a difficult time and throughout the development of the project. I really do appreciate all her effort, and without it, I would not be at this stage. It gives me immense pleasure to thank my co-supervisor, Dr. Caroline L. Peacock for her help, time, advice and patience. I am also grateful to my research collaborators, Dr. Tomasz M. Stawski, Dr. Davis J. Morgan, and Dr. Adriana Matamoros-Veloza. I really appreciate the Marie Skłodowska-Curie actions for sponsoring my PhD as part of the MINSC Initial Training Research Network and special thanks to the MINSC project manager, Clare Desplats. I would also like to thank all the PIs at the University of Leeds, Cohen geochemistry group, MINSC and CO2 react networks who guided me during my PhD. Thank you to the scientists at department of geosciences of University of Oslo specially Prof. Bjørn Jamtveit, Prof. Dag Dysthe, Prof. Håkon Olav Austrheim, and Kristina Dunkel for hosting me during my secondment. A special thank for Clariant Oil Services UK Ltd Company and Dr. Jamie Kerr and Dr. Adam Savin for providing me with an opportunity to have a short collaboration with them. v It is my pleasure to thank the administrative and technical staff, who were always available and helpful. Special thanks to Andy Connelly, Stephen Reid, Fiona Keay, Sam Allshaw, Richard Walshaw, Lesley Neave, Martin Fuller, Stuart Micklethwaite, and Mike Ward. I also want to thank my friends and colleagues at the University of Leeds, Cohen geochemistry group, MINSC and CO2 react networks. Thanks to Pilar Ramirez-Garcia, Juan- Diego Rodriguez Blanco, Andy Bray, Ekbal Hussain, Thomas Rinder, Giulia Montanari, Cristina Ruiz-Agudo, Andrea Arale Vidal, Ana Hernandez Rodriguez, Fernando Berro Jimenez, Stefanie Lutz, Jan Prikryl, Diwaker Jha, Deirdre Clark, Romain Guilbaud, and Santosh Narshima Prathap Moola. vi Abstract In this research, I focused on elucidating the crystallisation kinetics and formation mechanism of calcium sulfate phases, specifically gypsum, in the presence and absence of additives as inhibitors. In many industries such as oil production and water desalination, calcium sulfate formation is a problem that causes pipeline and membrane clogging and reduces system efficiency. Thus, different types of additives are added to these systems as inhibitors to tackle the scaling problem. However, their efficiency or effectiveness in terms of calcium sulfate inhibition has not been fully tested and the processes are not well-understood at the mechanistic level. In this thesis, therefore, I investigated the effects of various carboxylic acids, alkali / alkaline earth metal cations, polycarboxylic acids and phosphonates as gypsum inhibitors to fill this knowledge gap. My results revealed that all additives delayed the crystallisation of gypsum to various degrees and by various pathways. I monitored the change in the time needed for turbidity in a reacting solution to start (induction time) and develop (crystallisation kinetics). I analysed the changes in both solution chemistry and solid characteristics, including surface properties, morphologies as well as composition, to derive a mechanistic understanding of how these additives affect gypsum formation. The results illustrated that among the tested carboxylic acids (tartaric, maleic and citric), citric acid performed far better than tartaric and maleic (at equivalent concentrations) and using citric acid dramatically increased the induction time (~ 4 fold, to ~ 25 minutes). Among the tested alkali / alkaline earth metal cations (Li+,K+, Na+ and Mg2+), Mg2+ decreased the nucleation and growth kinetics ~ 5 to ~ 10 fold more than Li+, Na+ and K+ even vii at low concentrations. Mg2+, Li+ and K+ only adsorbed to the gypsum crystals surfaces, while ~ 25% of associated Na+ became incorporated into the synthesised crystals and Li+ and Mg2+ also acted as shape and size modifiers. When I tested the effects of biodegradable polycarboxylic additives (polyaspartic acid; PASP and polyepoxysuccinic acid; PESA) and compared their efficiency with a traditionally used non-biodegradable (polyacrylic acid; PAA) antiscalant, I showed that PASP and PESA had a profound effect on gypsum crystallisation, with PASP having the highest inhibition efficiency. The PAA conformation and molecular weight both played important roles in affecting the crystallisation kinetics because of changes in surface adsorption mechanisms. Finally, I tested some industrial phosphonate inhibitors and demonstrated that they are indeed strong gypsum inhibitors, but I also showed for the first time that an increase in the number of functional groups affected the efficiency of the additive. Among the tested phosphonates with five phosphonate functional groups, the one with longer molecular chains was the better inhibitor. It is unclear how these additives interacted with the growing gypsum crystals (surface adsorption and / or structural incorporation), but I clearly showed that they affected gypsum growth kinetics and morphologies. viii Table of Contents Declaration..................................................................................................................................i Dedication.................................................................................................................................iii Acknowledgements ..................................................................................................................iv Abstract.....................................................................................................................................vi Table of Contents ...................................................................................................................viii List of Figures..........................................................................................................................xii