AN INVESTIGATION OF THE DELIQUESCENCE OF FERRICOPIAPITE AND THE ONSET OF DELIQUESCENCE OF EPSOMITE CRYSTAL FACES OF DIFFERING MILLER INDICES by LOGAN ASTIN JAMESON A thesis submitted to the Department of Geological Sciences and Geological Engineering in conformity with the requirements for the degree of Masters of Science Queen's University Kingston, Ontario, Canada January, 2011 Copyright © Logan Astin Jameson, 2011 ABSTRACT Deliquescence is the process whereby a solid interacts with a humid atmosphere and begins to dissolve when the partial pressure of H2O in the atmosphere exceeds the partial pressure of H2O at which the solid is in equilibrium at a given temperature. Deliquescence of sulfate minerals poses a risk to both plant and animal life as metals and acid that are stored in the mineral structure are released. Detailed solid-solution transition boundaries for sulfate minerals aid in the understanding of acid mine waste behavior in the event of environmental changes. The deliquescence behaviors of ferricopiapite, melanterite, halite and epsomite have been studied as a function of temperature and relative humidity. A device has been developed to determine the onset of deliquescence as the temperature and/or relative humidity around a sample of sulfate mineral is varied. Experiments were conducted on several synthetic analogues of minerals. Ferricopiapite was studied as it is the most likely mineral to exhibit this behavior in common acid mine drainage sites where sulfates are present. Because no experimental data exist for the deliquescence of ferricopiapite, in order to properly test the device experiments in which the relative humidity was raised above the deliquescence point and then reversed were conducted using synthetic melanterite and halite for which solid-vapor equilibrium constants for temperature and relative humidity are known. Results of the reversal experiments for melanterite and halite show that the surface resistivity probe designed for this study accurately determines the onset of deliquescence as predicted by the known solid-liquid-vapor phase diagrams. The deliquescence of copiapite is not a reversible process as it does not re-precipitate from the liquid created by deliquescence as the relative humidity is lowered. Epsomite was studied to determine if there was any crystallographic control of the onset of deliquescence between different crystal faces. A significant and consistent difference in the onset of deliquescence was observed between the {111} and {100} faces with the {111} face always being the first to deliquesce as a function of increased relative humidity. i ACKNOWLEDGEMENTS I would like to thank Dr. Ron Peterson, my supervisor, for his knowledge, generous patience and the use of laboratory facilities. I would like to thank Al Grant for his support with the use of the X-ray diffractometer, SEM and sharing his knowledge. As well, I would like to thank Evelyne Leduc for her insight, help with lab equipment and support. I would like to also thank Sarah Rice for all of her help and advice. I would also like to thank Patrick van Kooten for all his advice, calm during stressful times and for always being there for me. Thank you to my parents, for always encouraging and supporting me. ii TABLE OF CONTENTS ABSTRACT ................................................................................................................................................... I ACKNOWLEDGEMENTS .........................................................................................................................II LIST OF TABLES ..................................................................................................................................... IV LIST OF APPENDICES ........................................................................................................................... VII DEFINITIONS ........................................................................................................................................ VIII CHAPTER 1: INTRODUCTION ............................................................................................................... 1 CHAPTER 2: MINERALOGY OF STUDY MINERALS ....................................................................... 5 FERRICOPIAPITE .......................................................................................................................................... 5 MELANTERITE ............................................................................................................................................. 5 HALITE ........................................................................................................................................................ 8 EPSOMITE .................................................................................................................................................... 8 CHAPTER 3: METHODS ......................................................................................................................... 13 TEMPERATURE AND HUMIDITY CHAMBER DESIGN ................................................................................... 14 SURFACE RESISTIVITY PROBE ................................................................................................................... 19 TEMPERATURE AND HUMIDITY CHAMBER CONTROL ................................................................................ 22 MINERAL SYNTHESIS ................................................................................................................................ 27 CHAPTER 4: RESULTS ............................................................................................................................ 29 FERRICOPIAPITE DELIQUESCENCE ............................................................................................................. 29 Melanterite Deliquescence................................................................................................................... 36 Halite Deliquescence ........................................................................................................................... 40 EPSOMITE DELIQUESCENCE ....................................................................................................................... 46 CHAPTER 5: DISCUSSION ..................................................................................................................... 52 FERRICOPIAPITE DELIQUESCENCE ............................................................................................................. 52 EPSOMITE DELIQUESCENCE ....................................................................................................................... 53 CHAPTER 6: CONCLUSIONS ................................................................................................................ 61 FUTURE WORK .......................................................................................................................................... 62 REFERENCES ............................................................................................................................................ 63 iii LIST OF TABLES Table 1 Expected and measured relative humidity values for various salts 17 at 30°C. Table 2 Formulae used in the calculation of relative humidity. 18 Table 3 Results for the Sensirion (SHT 1X) relative humidity verification. 24 Table 4 Deliquescence points for ferricopiapite crust. 32 Table 5 Deliquescence points for melanterite. 39 Table 6 Deliquescence points for halite. 45 Table 7 Results of epsomite deliquescence experiments. 51 iv LIST OF FIGURES Figure 1 Stability phases of some Fe3+ and Fe2+ minerals. 3 Figure 2 Sample of ferricopiapite crust. 6 Figure 3 Atomic structure of ferricopiapite. 7 Figure 4 Hydrogen Bonding Scheme of epsomite. 10 Figure 5 Epsomite crystal illustrations. 11 Figure 6 Atomic structure of epsomite. 12 Figure 7 Temperature and Humidity Control Chamber. 15 Figure 8 Temperature and Humidity Control Chamber Component 20 Placement. Figure 9 View of surface resistivity probe. 21 Figure 10 Information flow in Temperature and Humidity Control 26 Chamber. Figure 11 Change in relative humidity over time for ferricopiapite 31 experiment. Figure 12 Ferricopiapite, melanterite and halite deliquescence points. 33 Figure 13 XRD scan of ferricopiapite crust after deliquescence and re- 35 precipitation. Figure 14 Change in relative humidity over time for melanterite 37 experiment. Figure 15 Stability field of melanterite. 38 Figure 16 Change in relative humidity over time for halite experiments at 30°C and 35°C. 41 v Figure 17 Change in relative humidity over time for halite experiments 42 at 40°C and 45°C. Figure 18 Change in relative humidity over time for halite experiments 43 at 50°C. Figure 19 Deliquescence points for halite. 42 Figure 20 Synthesized epsomite crystal. 47 Figure 21 Stability field of epsomite. 48 Figure 22 Surface atoms for a particular slice, along the m (110) face of 55 epsomite as viewed 45° from the a and b axis Figure 23 Surface atoms for cross section of the m (110) face of 56 epsomite as viewed down the c axis. Figure 24 Surface atoms for a particular slice, along the l (111) face of 57 epsomite as viewed perpendicular to the face. Figure 25 Surface atoms for a particular slice, along the l (111) face of 58 epsomite as viewed perpendicular to the c axis and 45° from the a and b axis. Figure 26 Idealized diagram depicting dissolution pit formed on crystal 60 surface