THE CHARACTERIZATION, PERSISTENCE, AND BIOACCESSIBILITY OF ROASTER-DERIVED ARSENIC IN SURFACE SOILS AT GIANT MINE, YELLOWKNIFE, NT by Mackenzie Jane Bromstad A thesis submitted to the Department of Geological Sciences and Geological Engineering In conformity with the requirements for the degree of Master of Science Queen’s University Kingston, Ontario, Canada November, 2011 Copyright ©Mackenzie Jane Bromstad, 2011 Abstract Approximately 20,000 tonnes of arsenic (As)-bearing emissions from roasting arsenopyrite ore were aerially released from 1949-1999 at Giant Mine, located outside Yellowknife, NT. As part of the process used to free refractory gold (Au) from arsenopyrite (FeAsS), roasting created As-bearing roaster off-gases that condensed into As O , one of the most 2 3 toxic As compounds to humans. Roaster emissions also contained some As-bearing iron (Fe)- oxides. Arsenic emission controls were first implemented in 1951, and by the time the emission control process was completely refined in 1963, 86% of the total aerial As emissions at Giant had been released into the surrounding area. The continued presence of roaster-derived As O in 2 3 surface soils at Giant has been previously documented despite its theoretical instability in oxidizing surface environments. Wrye (2008) found As concentrations in roaster-affected soils occurring on rock outcrop (covering ~30% of the Giant property) greater than in many other surface soils; most outcrop soils were not considered when delineating areas of contaminated material for future removal in the Giant Mine Remediation Plan (currently undergoing environmental assessment). To investigate roaster-derived As persistence, outcrop soils and soil pore waters were analyzed. Comparing proportions of As, Sb, and Au concentrations in soil samples and historic As O -rich dust captured by emission controls show that most of the roaster-derived As in soils at 2 3 Giant was likely deposited before 1964. Thin section examination has shown that while the vast majority of discrete As hosts in soils are As O , textural relationships and certain secondary As 2 3 hosts in soils indicate that As O is not static in surface soils and could be transforming over time, 2 3 albeit very slowly. Bulk chemical relationships among As, antimony (Sb), and carbon support this. Topographic restriction by rock outcrops and dry, cold climate probably play a large role in elevated As concentrations and As O persistence in outcrop soils. In light of possible future 2 3 human exposure, As bioaccessibility from three adjacent samples was determined for synthetic human gastric (34%) and lung (18%) fluids. ii Co-Authorship A different version Chapter 1 of this thesis, co-authored with H.E. Jamieson, was submitted for publication as Chapter 2 in the book The Metabolism of Arsenite edited by J. Santini and S. Ward. Chapters 4 and 5 of this thesis were prepared as manuscripts for journal publication. Chapter 4 is co-authored with H.E. Jamieson. Chapter 5 is co-authored with H.E. Jamieson, S. Morman, and G.S. Plumlee. H.E. Jamieson conceived the entire project, acted in a supervisory and review capacity for the entire duration, contributed to geochemical interpretations and was involved in field work and synchrotron data interpretation. S. Morman and G.S. Plumlee provided expertise on and performed bioaccessibility testing through the United States Geological Survey. iii Acknowledgements First and foremost I would like to thank my supervisor Dr. Heather Jamieson. I appreciate her constant support and guidance so much, and especially her contagious enthusiasm for my project and environmental geochemistry in general. It has made a huge difference in my time at Queen’s. All the members of Dr. Jamieson’s research group have been invaluable in their support, both emotional and educational, in far too many ways to list. I have been lucky to be the recipient of the wisdom, experience, and friendship of this great group of people. Cirisse Stephen deserves a special thanks for being quite possibly the best field assistant I could imagine. Her limitless enthusiasm, positive attitude, incredible energy, propensity to deposit delicious meals in front of me when I was too distracted to remember to eat, and generally amazing company made my field season incredible. Thank you also to other members of the geology department who have helped me, and to all my friends for being there when I have needed them and generally making this a great experience. Thank you especially to Geoff for being so supportive and understanding (these two words being grossly inadequate descriptions of what you’ve done), and to all my partners in making music for providing an amazing experience to compliment my time at Queen’s. Thank you to the people who have helped my research along the way, including Al Grant in the Department of Geological Sciences, Dr. Tony Lanzirotti at NSLS, Chris Grooms from Dr. Smol’s PEARL lab, Patricia Hunt from the Geological Survey of Canada, and Linda Campbell from Dr. Grogan’s lab. Thanks to Benny Nordahn and the workers at Deton ‘Cho Nuna at Giant Mine for your assistance and gracious accommodation of my field work. Thank you to Indian and Northern Affairs Canada for allowing me access to the Giant Mine site. Finally, I can never thank my parents, Julie and Peter Bromstad, enough for their unwavering support, and belief in me over the years in too many ways to list. Thank you also to iv my sisters Chelsea and Talia, David, and the rest of my family for their consideration and patience during this crazy time in my life. v Table of Contents Abstract…………………………………………………………………………………………...ii Co-Authorship…………………………………………………………………………………...iii Acknowledgements………………………………………………………………………………iv List of Figures ..................................................................................................................................x List of Tables .................................................................................................................................xii List of Appendices. .......................................................................................................................xiii Chapter 1: Introduction and background .....................................................................................1 1.1 Introduction ..........................................................................................................................1 1.2 Background ...........................................................................................................................3 1.2.1 Physiographic setting ..................................................................................................3 1.2.2 Geologic setting ..........................................................................................................5 1.2.3 History of mining and processing at Giant .................................................................8 1.2.4 Mine management, ownership, and responsibility for remediation .........................11 1.3 Arsenic in mine waste and surrounding area ......................................................................12 1.3.1 Surface and mine water .............................................................................................12 1.3.2 As in solid media at Giant Mine ................................................................................14 1.3.2.1 Mine tailings ..............................................................................................................14 1.3.2.2 Roaster Waste (Calcine, ESP Dust, Underground storage, stack emissions) ............14 1.3.2.3 Sediments ...................................................................................................................17 1.3.2.4. Soil ............................................................................................................................17 1.4 Giant Mine remediation .....................................................................................................20 1.5 Research objectives ............................................................................................................22 Chapter 2: Literature review .......................................................................................................24 2.1 Arsenic in the environment ................................................................................................24 2.1.1 Sources of arsenic .....................................................................................................24 2.1.2 Characterization of primary arsenic hosts in roaster-impacted soils ........................25 2.1.3 Stability and mobility of arsenic in surface soils and porewaters .............................27 2.1.3.1 Secondary arsenic phases ..........................................................................................29 2.1.3.2 Arsenic adsorption .....................................................................................................32 2.1.3.2 Effect of reaction kinetics on redox ............................................................................35 2.1.4 Studies on the transformation and persistence of As2O3 in soils .............................36 2.2 Toxicity and bioaccessibility of arsenic .............................................................................38 vi 2.2.1 Toxicity of arsenic .....................................................................................................38 2.2.2 Measuring bioaccessibility and bioavailibility of arsenic .........................................40 2.2.2.1 Gastric bioaccessibility models for arsenic ...............................................................41 2.2.2.2 Lung bioaccessibility models for arsenic ...................................................................44 2.2.3 Soil properties effecting arsenic bioavailability .......................................................46 2.2.4 Bioaccessibility and bioavailability of arsenic in mining environments ..................48 2.2.4.1 Gastric bioaccessibility and bioavailability ..............................................................48 2.2.4.2 Lung bioaccessibility and bioavailability ..................................................................50 Chapter 3: Field and analytical methods ....................................................................................52 3.1 Field sampling sites ............................................................................................................52 3.1.1 Soil sampling sites ....................................................................................................54 3.1.2 Bulk soil bioaccessability sampling sites ..................................................................55 3.1.3 Soil water sampling sites ..........................................................................................55 3.2 Field methods .....................................................................................................................56 3.2.1 Soil sample collection ...............................................................................................56 3.2.2 Bioaccessibility bulk soil sample collection .............................................................58 3.2.3 Vadose zone water sample collection .......................................................................59 3.3 Analytical methods: soils ....................................................................................................62 3.3.1 Elemental analysis .....................................................................................................62 3.3.2 Bulk sample sieving and elemental analysis of samples used for bioaccessibility testing .................................................................................................................................63 3.3.3 Carbon and nitrogen analysis ....................................................................................63 3.3.4 Petrographic thin section preparation and examination ............................................64 3.3.5 Environmental Scanning Electron Microscopy (ESEM) ..........................................65 3.3.6 Synchrotron-based methods ......................................................................................66 3.3.6.1 µXRF mapping ...........................................................................................................67 3.3.6.2 Micro-XRD analysis ...................................................................................................68 3.3.6.3 Micro-XANES analysis ..............................................................................................69 3.4 Analytical methods: bioaccessibility ..................................................................................69 3.5 Analytical methods: vadose waters .....................................................................................72 Chapter 4: The characterization, mobility, and persistence of roaster-derived Arsenic in soils at Giant Mine, NT .................................................................................................................73 4.1 Introduction ........................................................................................................................73 4.1.1 Site background .........................................................................................................73 4.1.2 Known forms of roaster-generated As in soils at Giant ............................................75 4.1.3 Roaster dust composition ..........................................................................................75 vii 4.1.4 Relative mobility and stability of roaster dust components ......................................76 4.1.5 Physiographic setting ................................................................................................78 4.2 Methods ..............................................................................................................................79 4.2.1 Field sampling ...........................................................................................................79 4.2.2 Analytical methods ....................................................................................................81 4.2.2.1 Bulk chemistry analysis ..............................................................................................81 4.2.2.2 Thin section preparation ............................................................................................82 4.2.2.3 Environmental scanning electron microscopy (ESEM) ..............................................83 4.2.2.4 Synchrotron-based methods .......................................................................................83 4.3 Results ................................................................................................................................86 4.3.1 Bulk chemistry ..........................................................................................................86 4.3.2 Arsenic hosts .............................................................................................................88 4.4 Discussion ..........................................................................................................................94 4.4.1 Bulk chemical associations .......................................................................................94 4.4.2 Arsenic host mobility ................................................................................................98 4.4.3 Age of roaster-derived As ........................................................................................101 4.5 Conclusions ......................................................................................................................106 Chapter 5: Gastric and lung bioaccessibility of arsenic in soil contaminated by roaster emissions at Giant Mine, NT ......................................................................................................108 5.1 Introduction ......................................................................................................................108 5.2 Methods ............................................................................................................................112 5.2.1 Elemental analysis and thin section construction ...................................................114 5.2.2 Environmental scanning electron microscopy and synchrotron methods ...............115 5.2.2.1 Micro-XRF mapping ................................................................................................117 5.2.2.2 Micro-XRD analysis .................................................................................................117 5.2.2.3 Micro-XANES analysis ............................................................................................118 5.2.3 Gastric and lung bioaccessibility testing .................................................................118 5.3 Results ..............................................................................................................................120 5.3.1 Arsenic hosts and bulk chemistry ............................................................................120 5.3.2 Arsenic bioaccessibility results ...............................................................................123 5.4 Discussion and conclusions ..............................................................................................125 Chapter 6: Conclusions and future work .................................................................................131 6.1 Conclusions ......................................................................................................................131 6.2: Future work .....................................................................................................................133 References ....................................................................................................................................135 APPENDIX I: Sample analysis and GPS coordinate list ........................................................152 viii APPENDIX II: Bulk chemistry results, ACME Laboratories ................................................157 APPENDIX III: Bulk chemistry results, USGS .......................................................................161 APPENDIX IV: Carbon and nitrogen results ..........................................................................163 APPENDIX V: Gastric and lung in vitro leach and percent bioaccessibility results ............166 APPENDIX VI: Soil pore water results ....................................................................................169 APPENDIX VII: Platinum electrode ORP results ...................................................................171 APPENDIX VIII: Sample site photographs and soil sample descriptions ............................173 APPENDIX IX: Petrographic, ESEM, and synchrotron target identification .....................177 APPENDIX X: Giant Mine property maps with arsenic concentrations ..............................181 ix List of Figures 1.1 Location of Giant Mine………………………………………………………………………...4 1.2 Giant Mine geology……………………………………………………………………………6 1.3 Schematic of roasting process………………………………………………………………….9 1.4 Air photo of Giant Mine………………………………………………………………………10 2.1 Eh-pH phase diagrams for As………………………………………………………………...28 2.2 As(III) and As(V) adsorption on Fe oxyhydroxides………………………………………….34 2.3 As(III) and As(V) adsorption on Mn and Fe oxyhydroxides…………………………………35 2.4 Factors affecting As bioaccessibility…………………………………………………………47 3.1 Map of summer 2010 sample locations………………………………………………………53 3.2 Three outcrop sample location photos with variable geology, soil amount, and lichen and vegetation cover………………………………………………………………………….……….54 3.3 Sample locations at site 8……………………………………………………………………..56 3.4 Lysimeter installation…………………………………………………………………………60 3.5 As O and ROs, BSE v. plain light……………………………………………………………66 2 3 3.6 µXRF analyses………………………………………………………………………………..68 3.7 µXANES standard spectra……………………………………………………………………70 4.1 Giant Mine summer 2010 sample locations………………………………………………….80 4.2 µXANES standard spectra……………………………………………………………………86 4.3 Bulk chemistry As and Sb results by carbon content…………………………………………87 4.4 BSE images of As O ………………………………………………………………………...89 2 3 4.5 RO synchrotron identification………………………………………………………………..90 4.6 Summary of µXANES data for As hosts previously undocumented in Giant Mine soils…...91 4.7 2-D µXRD for sample 35_2-6……………………………………………………………….92 4.8 Fe and As µXRF data for sample B2a-4…………………………………………………….92 4.9 Pyrite with As-bearing Fe-oxyhydroxide weathering rims and Fe-As µXRF maps………...93 4.10 As v. C and Sb v. C for outcrop soils ……………………………………………………...94 4.11 As v. Sb plots for outcrop soils …………………………………………………………….96 4.12 Coexisting soil pore water relationships for As, Sb, and C………………………………...97 4.13 pH-Eh diagrams for aqueous As with pore waters…………………………………………99 4.14 As, Sb, and Au plots showing background soil composition (Kerr 2006). outcrop soil data, and pre- and post-1964 ESP dust composition…………………………………………………104 x