AN INVESTIGATION INTO THE LEACHING OF ENARGITE UNDER ATMOSPHERIC CONDITIONS by Mark Zachary Gupta A thesis submitted to the Robert M. Buchan Department of Mining In conformity with the requirements for the degree of Master of Applied Science Queen’s University Kingston, Ontario, Canada (May, 2010) Copyright © Mark Zachary Gupta, 2010 Abstract The leaching behaviour of enargite was studied under atmospheric pressure. The kinetics of enargite dissolution appear to be extremely slow under the conditions studied using both small scale shake flasks and bench scale stirred tank reactors. An enargite concentrate and a purer mineral specimen were utilized and the effect of numerous variables including temperature, particle size, acidity, oxygen flow rate, iron addition, redox potential and pyrite addition were investigated. The initial rate of copper dissolution from enargite was relatively fast up to about 40% copper extraction but this was followed by a much slower dissolution rate. The first stage is thought to be reaction rate controlled while the latter stage appears to be diffusion controlled. The activation energy was determined to be 32 kJ/mol for the concentrate and 33 kJ/mol for the pure specimen in the temperature range of 55-85°C. In the presence of high concentrations of copper sulphate, enhanced copper recovery was observed for the pure enargite specimen. This could be the result of a change in the reaction product layer on the enargite surface and perhaps the formation of intermediate Cu2S. Previous work has shown that adding excess pyrite enhances copper extraction from enargite but these results could not be reproduced. Particle size reduction appears to be the most effective method to increase extraction rates, however only 70% copper recovery and 35% arsenic recovery was achieved after 24 hours of leaching at d80=2µm. At these reaction rates, it appears that enargite dissolution at atmospheric pressure will not be an economical process compared to other technologies such as high temperature/pressure oxidation or roasting. ii Acknowledgements First and foremost I would like to thank Dr. John Peacey for all of his advice and guidance during my time as a graduate student. Maritza Bailey’s assistance in the laboratory was instrumental and greatly appreciated. A special thanks goes out to all my friends and family who supported me throughout my Master’s. Finally, I would like to acknowledge NSERC and Xstrata Plc. for funding this project. iii Table of Contents Abstract ............................................................................................................................................ ii Acknowledgements.........................................................................................................................iii Chapter 1 Introduction ..................................................................................................................... 1 Chapter 2 Literature Review............................................................................................................ 3 2.1 Background Chemistry .......................................................................................................... 3 2.1.1 Proposed Reaction Mechanisms for Chalcopyrite and Enargite Leaching..................... 3 2.1.2 Oxidation/Reduction Potential...................................................................................... 10 2.1.3 Addition of Ionic Species.............................................................................................. 16 2.2 Operating Parameters of Interest ......................................................................................... 21 2.2.1 Particle Size .................................................................................................................. 21 2.2.2 Temperature .................................................................................................................. 23 2.2.3 Acid Concentration ....................................................................................................... 26 2.2.4 Agitation ....................................................................................................................... 29 2.2.5 Oxygen Partial Pressure................................................................................................ 31 2.2.6 Chloride Addition ......................................................................................................... 33 2.2.7 Pyrite Addition.............................................................................................................. 36 2.3 Summary .............................................................................................................................. 39 Chapter 3 Materials and Methods .................................................................................................. 40 3.1 Enargite Sample Characteristics .......................................................................................... 40 3.2 Shake Flask Experiments..................................................................................................... 43 3.3 Bench Scale Experiments .................................................................................................... 43 Chapter 4 Results and Discussion.................................................................................................. 45 4.1 Shake Flask Tests................................................................................................................. 45 4.1.1 Pulp Density, Acidity, and Chloride Concentration ..................................................... 45 4.1.2 Temperature, Acidity, and Chloride Concentration...................................................... 48 4.1.3 Iron Addition and Particle Size..................................................................................... 52 4.1.4 Ion Effects on Enargite Concentrate ............................................................................. 55 4.1.5 Statistical Model for the Enargite Concentrate............................................................. 65 4.1.6 Ion Effects on the Pure Enargite Specimen .................................................................. 69 4.1.7 Statistical Model for the Pure Enargite Specimen ........................................................ 77 iv 4.1.8 Comparison Between Concentrate and Pure Enargite .................................................. 80 4.2 Bench Scale Tests on the Enargite Concentrate................................................................... 85 4.2.1 Temperature .................................................................................................................. 85 4.2.2 Oxygen Partial Pressure................................................................................................ 90 4.2.3 Pulp Density.................................................................................................................. 92 4.2.4 Iron Addition................................................................................................................. 96 4.2.5 Acidity........................................................................................................................... 99 4.2.6 Chloride Addition ....................................................................................................... 102 4.2.7 Pyrite Addition............................................................................................................ 106 4.2.8...................................................................................................................................... 114 4.2.8 Particle Size ................................................................................................................ 114 4.3 Bench Scale Tests on the Enargite Mineral Specimen ...................................................... 118 4.3.1 Temperature ................................................................................................................ 118 4.3.2 Chloride....................................................................................................................... 127 4.3.3 Iron.............................................................................................................................. 129 4.3.4 Pyrite ........................................................................................................................... 131 4.3.5 Copper Sulphate Addition.......................................................................................... 134 Chapter 5 Conclusions and Future Work..................................................................................... 141 5.1 Conclusions........................................................................................................................ 141 5.2 Areas of Future Work ........................................................................................................ 143 References.................................................................................................................................... 145 Appendix...................................................................................................................................... 151 7.1 Raw Data............................................................................................................................ 152 7.2 Statistical Models..............................................................................................................