Characterisation of the liberation kernel Snezana Bajic Bachelor of Science, Bachelor of Engineering A thesis submitted for the degree of Doctor of Philosophy at The University of Queensland in 2014 Sustainable Minerals Institute Abstract Liberation is a fundamental process of mineral processing for almost all ores. A long- standing and challenging problem is the estimation of the liberation kernel in comminution. In this context the kernel means the mathematical transformation which relates the feed sizing and liberation distribution presented to a breakage or comminution device to the size or liberation distribution of the progeny. Previously it was difficult to adequately quantify the liberation status of the feed particles without size reduction in order to prepare adequate samples for various two dimensional analysis methods. This destructive preparation process would not only change the size of the parent particle, but also lead to destruction of texture and liberation information. The texture information of a feed material is defined as the internal arrangement of mineral grains, their size and spatial distribution. Earlier work has been almost entirely restricted to binary composites which may be non-destructively classified by particle density and/or magnetic susceptibility or electrical conductivity. (Wiegel 1976b, 2006; Wiegel and Li 1967) Micro-cone Beam Tomography (Micro CBT) was used for sorting feed particles into different composition classes and into different texture classes before breakage. While this technology still does not provide as wide a range of mineral differentiation or resolution as might be desired it is a significant advance over earlier approaches. The grains are observed in three dimensions by analysing Micro CBT cross sectional images using eCognition image analysis software. The image analysis method developed in this Thesis enables the user to adequately characterise texture and liberation of the parent particle and progeny particles in three dimensions. A range of methods for quality assurance have also been established. The validation of mineral classification was performed using the Mineral Liberation Analyser (FEI, 2014). This technology provides excellent mineral recognition at high resolution. 2 The method developed here measures intact particle texture and allows for measurement of the texture and liberation of the progeny particles with no destruction of the particles. The sample preparation process for Micro CBT does not involve any physical damage to the particles. The full composition of the parent and its progeny particles can be measured in three dimensions using this method. A random breakage model prediction has been presented where the measured liberation of progeny created by breaking the parent particle was compared with the liberation simulated by cutting the Micro CBT reconstructed two dimensional images of the parent particle into different size cubes. The measured degree of liberation of the progeny particles confirms that below a certain particle size, liberation becomes selective as previously observed by Wiegel (2006). The random simulation of breakage helped reveal liberation by size reduction. The selective breakage identified in this research plays a major role especially in the range where the particle to grain size ratio is 1. There was a tendency for the gangue to break into the coarser liberated particles, unlike the valuable phase which has a tendency to break into finer, liberated particles. The need for a detachment factor (Hsih and Wen 1994) to be incorporated into random liberation models was confirmed. In many cases, the predicted grind size required to liberate gangue sufficiently may be the most useful outcome of the measurement. Although available techniques, such as MLA, provide excellent mineral recognition at high resolutions, the two dimensional mineral data obtained needs to be adjusted to estimate three-dimensional characteristics. This process is called stereological adjustment and the degree of adjustment depends on ore texture. The new technology can be used for testing the methods of stereological adjustments. Improved measurement of liberation leads to an improved understanding and the possibility of optimisation of the process of liberation. This Thesis brings the new testing technology which can be used to characterise the liberation kernel, that is to predict the 3 liberation distribution which would occur at any reasonable degree of liberation, for a known ore type and a known energy. 4 Declaration by author This Thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my Thesis. I have clearly stated the contribution of others to my Thesis as a whole, including statistical assistance, survey design, data analysis, significant technical procedures, professional editorial advice, and any other original research work used or reported in my Thesis. The content of my Thesis is the result of work I have carried out since the commencement of my research higher degree candidature and does not include a substantial part of work that has been submitted to qualify for the award of any other degree or diploma in any university or other tertiary institution. I have clearly stated which parts of my Thesis, if any, have been submitted to qualify for another award. I acknowledge that an electronic copy of my Thesis must be lodged with the University Library and, subject to the General Award Rules of The University of Queensland, immediately made available for research and study in accordance with the Copyright Act 1968. I acknowledge that copyright of all material contained in my Thesis resides with the copyright holder(s) of that material. Where appropriate I have obtained copyright permission from the copyright holder to reproduce material in this Thesis. 5 Publications during candidature Introduction to X-Ray microtomography, ICAM Sep 2008, workshop presentation The use of Cone Beam Tomography for identifying and quantifying minerals, 2008, JKMRC SMI RHD Conference paper (Chapter 3 and appendix 9.12 data) Quantitative analyses of minerals in multiphase particles using X-Ray microtomography procedures, 2010, JKMRC SMI RHD Conference paper, The University of Queensland (Chapter 5) Characterisation of liberation kernel, public presentation at JKMRC, confirmation of candidature June 2011 (Chapters 2 to 5) Publications included in this Thesis No publications included 6 Contributions by others to the Thesis I received advice and support from the supervisors of this PhD research work: - Dr Rob Morrison supported the research work from its beginning. His help in concept and the design of the Thesis, as well as in data interpretation and writing was priceless. - Dr Cathy Evans joined the project in its last two years. She supported it in every aspect and gave very important advice in drafting of the Thesis, data interpretation and writing. I received research assistance from: - Dr Tim Napier-Munn for some statistical analysis of the data. He also made a significant contribution during the Thesis reviews, where he expressed his opinion on the data and pointed in important research design directions. I received advice and support from: - Dr Luke Keeney on micro tomography imaging. - Dr Richard Hartner on image analysis and image registration. - Dr Steve Larbi-Bram on RBT data. - Ion Gurnett in 2009 published Ore Characterisation of Dense Medium Separated Particles by Cone Beam Tomography and MLA Analysis as his Undergraduate Thesis at The University of Queensland. Ion was supervised by Dr Rob Morrison and me. His research data helped in defining some measurement and analysis parameters for this research. The images were from Murat Cakici, 2009, 'Characterisation of Samples of Ore Particles using X-Ray Microtomography', Master of Philosophy Thesis, The University of Queensland. 7 Statement of parts of the Thesis submitted to qualify for the award of another degree None 8 Acknowledgements "Scio me nihil scire." "I know that I know nothing." Socrates This life-changing PhD journey would not have been possible without the support and guidance that I have received from many people. Everything I achieved I own to, and share with the people below. This PhD started with the encouraging conversations with Dr Aleksandar Janković in 2005. My deep appreciation goes to him and his family for their priceless help in the early days of my settlement. I will forever be thankful to my mentor Dr Robert Morrison. You are the supervisor everybody could wish to have, a blessing from the God. It is your encouragement that was giving me the strength to continue. Without your guidance and constant feedback this PhD would not have been achievable. Many thanks to Dr Catherine Evans for her support, patience and guidance. Your help and understanding were precious. Rob and Cathy are my dream supervisory team, I could not have asked for better role models. I am very proud of my JKMRC team and I truly hope I will continue to share the research values, dreams and wisdom that you have given to me. Special thanks and gratitude goes to Julius Kruttschnitt Mineral Research Centre (JKMRC), a place which would always bring special nice memories in my hearth. I am also very grateful to all those at JKMRC, especially Jill, Karen, Leith, Sherrin, Neva, Mike, Ton and Ray, who were always so helpful and provided me with their assistance every time. Thanks to the Pilot Plant and MLA laboratory staff for their help during my experimental work. Many thanks to Dr Tim Napier-Munn for his valuable inputs and ideas. Without the use of Dr Matt Brennan’s “powerful” computer the work would not be possible. Thanks to my student colleagues Richard, Luke and many others at JKMRC. I would also like to thank Dr Steve Morrell and Dr Toni Kojović for their support and many encouraging conversations. 9 I gratefully acknowledge the funding received towards my PhD from the JKTech Pty Ltd.