FERRIC SULPHATE LEACHING OF PYRRHOTITE TAILINGS by Nazanin Samadifard A thesis submitted in conformity with the requirements for the degree of Master of Applied Science Graduate Department of Chemical Engineering and Applied Chemistry University of Toronto © Copyright by Nazanin Samadifard 2015 Ferric Sulfate Leaching of Pyrrhotite Tailings Nazanin Samadifard Master of Applied Science Department of Chemical Engineering and Applied Chemistry University of Toronto 2015 Abstract The present study investigates the potential to recover nickel from pyrrhotite tailings produced at the smelting operations of Vale in Sudbury, Ontario. Leaching tests were performed in acidic ferric sulphate media with 0.14 wt.% solids. The temperature was varied between 30 °C and 55 °C, and the ferric concentration was in a range 0.02- 0.3 M. The shrinking core model (SCM) was applied on the nickel extraction data. The dominant reaction mechanism was found to be diffusion control. The Arrhenius plot yielded an activation energy of Ea=62.12 kJ/mol based on apparent reaction rates obtained by the SCM. The reaction order with respect to ferric ion was found to be 1.0 at the high concentration range. SEM images of partially leached tailings confirmed the presence of elemental sulphur around the pyrrhotite particles, which was responsible for the observed non-linear leaching kinetics (diffusion control). ii Acknowledgments I would like to express my sincere appreciation to my supervisor Dr. Vladimiros Papangelakis for his constant support, guidance and patience throughout the course of my study. Financial support of Vale Canada, Glencore, the Ontario Centers of Excellence (OCE), the Centre for Excellence in Mining Innovation (CEMI), and the Natural Sciences and Engineering Research Council of Canada (NSERC) are gratefully acknowledged. I would extend my grateful thanks to Dr. Cheryl Washer for being a great consultant in the later stages of my project, and other members of APEC laboratory for their friendship, guidance and generosity. The most sincere gratitude goes to my parents and my lovely family for their support and encouragement in all aspects of my life. Finally, I dedicate this thesis to my dear husband Mohammadreza Dadkhah for his unconditional love and support during the completion of my master’s degree. iii Table of Contents Acknowledgments ..................................................................................................................... iii List of Tables .............................................................................................................................vii List of Figures .......................................................................................................................... viii Abbreviations ............................................................................................................................... x Chapter 1: Introduction ................................................................................................................ 1 1.1 Overview ....................................................................................................................... 1 1.2 Research scope .............................................................................................................. 2 1.3 Objectives ..................................................................................................................... 2 1.4 Thesis organization ....................................................................................................... 2 Chapter 2: Literature review ........................................................................................................ 4 2.1 Nickeliferous pyrrhotite tailings ................................................................................... 4 2.2 Pyrrhotite ....................................................................................................................... 6 2.3 Dissolution pathways of pyrrhotite ............................................................................... 6 2.3.1 Oxidative dissolution ............................................................................................. 6 2.3.2 Non-oxidative dissolution ...................................................................................... 7 2.4 Factors affecting pyrrhotite oxidation ........................................................................... 8 2.4.1 Crystal structure ..................................................................................................... 8 2.4.2 Oxygen ................................................................................................................... 9 iv 2.4.3 Ferric ion concentration ......................................................................................... 9 2.4.4 Temperature ........................................................................................................... 9 2.5 Oxidation-reduction potential ..................................................................................... 10 2.6 Shrinking core model .................................................................................................. 11 2.7 Passivation .................................................................................................................. 13 Chapter 3: Materials and experimental procedures ................................................................... 15 3.1 Materials ..................................................................................................................... 15 3.2 Characterization of pyrrhotite tailings ........................................................................ 15 3.2.1 Particle size distribution ...................................................................................... 15 3.2.2 Chemical characterization ................................................................................... 16 3.2.3 Mineralogical characterization ............................................................................ 17 3.3 Leaching tests .............................................................................................................. 18 3.4 Analytical techniques .................................................................................................. 19 3.4.1 ICP analysis ......................................................................................................... 19 3.4.2 Potassium dichromate titration ............................................................................ 20 3.4.3 HPLC analysis ..................................................................................................... 20 3.4.4 SEM analysis ....................................................................................................... 21 3.5 Elemental sulfur determination ................................................................................... 21 Chapter 4: Results and discussions ............................................................................................ 23 4.1 Effect of temperature on nickel extraction .................................................................. 23 4.2 Effect of ferric sulphate concentration on nickel extraction ....................................... 27 v 4.3 Elemental sulphur generation during leaching............................................................ 30 4.4 Morphology of elemental sulphur ............................................................................... 36 Chapter 5: Conclusions .............................................................................................................. 39 References.................................................................................................................................. 41 Appendices ................................................................................................................................ 45 Appendix A. Nickel extraction kinetics at different temperatures......................................... 45 Appendix B. Ferric sulphate concentration effect on nickel extraction ................................. 53 Appendix C. Elemental sulphur determination ...................................................................... 63 Appendix D. SEM images and EDX Spectra ........................................................................ 72 vi List of Tables Table 2-1. Activation energies obtained for oxidation of pyrrhotite and pentlandite. .............. 10 Table 2-2. ORP correction factors for different reference electrodes. ...................................... 11 Table 2-3. Shrinking core model mechanisms. ......................................................................... 13 Table 3-1. Elemental composition of pyrrhotite tailings. .......................................................... 17 Table 3-2. Mineralogical composition of pyrrhotite tailings. .................................................... 17 Table 4-1. Diffusion-control apparent rate constant values at various temperatures. ............... 26 Table 4-2. Chemical reaction-control apparent rate constant values at various temperatures. 26 Table 4-3. Diffusion-control apparent rate constants at various ferric sulphate concentrations. ................................................................................................................................................... 29 vii List of Figures Figure 2-1. Schematic diagram of the SCM. ............................................................................