Geochemical Reactions in Unsaturated Mine Wastes Jeanette K. Jerz Dissertation submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Geological Sciences Committee in charge: J. Donald Rimstidt, Chair James R. Craig W. Lee Daniels Patricia Dove D. Kirk Nordstrom April 22, 2002 Blacksburg, Virginia Keywords: Acid Mine Drainage, Pyrite, Oxidation Rate, Efflorescent Sulfate Salt, Paragenesis, Copyright 2002, Jeanette K. Jerz GEOCHEMICAL REACTIONS IN UNSATURATED MINE WASTES JEANETTE K. JERZ ABSTRACT Although mining is essential to life in our modern society, it generates huge amounts of waste that can lead to acid mine drainage (AMD). Most of these mine wastes occur as large piles that are open to the atmosphere so that air and water vapor can circulate through them. This study addresses the reactions and transformations of the minerals that occur in humid air in the pore spaces in the waste piles. The rate of pyrite oxidation in moist air was determined by measuring over time the change in pressure between a sealed chamber containing pyrite plus oxygen and a control. The experiments carried out at 25˚C, 96.8% fixed relative humidity, and oxygen partial pressures of 0.21, 0.61, and 1.00 showed that the rate of oxygen consumption is a function of oxygen partial pressure and time. The rates of oxygen consumption fit the expression dn −− O2 = 10 648...Pt 05 05. dt O2 It appears that the rate slows with time because a thin layer of ferrous sulfate + sulfuric acid solution grows on pyrite and retards oxygen transport to the pyrite surface. The transformation of efflorescent sulfate minerals (the reaction products of iron sulfide oxidation) from a pyrrhotite-rich massive sulfide is explained using a systematic analysis of their stoichiometry and thermodynamics. Their stabilities are controlled by oxygen partial pressure, relative humidity, and activity of sulfuric acid and can be visualized using logaa− log and logaa− log diagrams developed during OHO22 HSO24 HO 2 this study. Samples from the field site were analyzed in the laboratory to determine mineralogy, equilibrium relative humidity, chemical composition, and acid generation potential. Dissolution experiments showed that fibroferrite-rich samples had the highest acid producing potential, followed by copiapite-rich samples and then halotrichite-rich samples. The most abundant metals in solutions produced by dissolving the salts were magnesium, aluminum, zinc, copper, calcium, and lead. The molar concentrations of the metals varied with mineralogy. However, all of these minerals release metals and acid when they dissolve and therefore represent a significant environmental threat. iii “All Things are Poisonous and yet there is Nothing that is Poisonous; it is only the Dose that makes a Thing Poisonous” --P.A. Paracelsus iv GRANT INFORMATION This project was made possible by funding from the following: - The National Science Foundation (Grant EAR-0003364) - The Waste Policy Institute - The Department of Geological Sciences - The David Wones Geologic Scholarship Fund - The Graduate Student Assembly v ACKNOWLEDGEMENTS First and foremost, I would like to thank my advisor, Don Rimstidt, for his assistance, advice, and support during my Ph.D. Don has always been available to help me, not only with this project, but also with all other areas of my profession development. I will always be indebted to him for the time and attention he has given me. I would like also like to thank the other members of my committee: James Craig, Lee Daniels, Patricia Dove, and Kirk Nordstrom. Over the years, all of my committee members have provided me a great deal of technical assistance, scientific perspective, and personal guidance. I feel truly fortunate to have such a contributive and invaluable committee. In addition, I would like to thank several people who helped me with this project: - Dan Smith for building the Barcroft apparatus and stand and for generally contributing his skills and knowledge; - Heather Shannon for help in the field and lab, especially with the sulfate mineral relative humidity and acid production experiments; - Jane Hammarstrom and Nadine Piatak (USGS) and Ross Angel (VT) for help with identifying the sulfate minerals; - Rob Weaver for his time and microscopy skills; - Treavor Kendall and Steven Lower for analyzing my samples for bacteria and general discussions of microbes; - All the present and past faculty and graduate students of the Geochemistry Research Group (Don, Mike, Chris, Trish, Nancy, Ross, Maddy, John, Russ, Kevin, Jody, Barry, Eric, Steven, Rob, Erin, Treavor, Tracy, Stacy, Jackson, Andy, Collin, Kevin, Brenda, Mariano, and Darren), who have provided great amounts of scientific discourse and generally support during my tenure at Virginia Tech. vi I would also like to thank the faculty and staff of the Department of Geological Science at Virginia Tech for providing me with an excellent education and an opportunity to pursue my professional goals. Specifically, I am grateful to Cahit Coruh for his vision and leadership of the department while I was here. Also, I appreciate Linda Bland, Mary McMurry, Connie Lowe, Carolyn Williams for always being available and helpful and for making everything go as smoothly as possible. Finally I would like to thank my friends and family who have loved and supported me through out this project. Specifically, I would like to thank my Mom, Dad, brother Jim, and Jason; without them this never would have happened. vii TABLE OF CONTENTS Abstract ..................................................................................................................................ii Grant Information ...................................................................................................................v Acknowledgements................................................................................................................vi Table of Contents.................................................................................................................viii List of Figures.........................................................................................................................x List of Tables.........................................................................................................................xi Chapter 1 : Introduction .........................................................................................................1 Chapter 2 : Pyrite oxidation in moist air ................................................................................1 Abstract ..................................................................................................................................1 Introduction ............................................................................................................................2 Materials and Methods............................................................................................................5 Reactor Design....................................................................................................................6 Experimental Procedure ......................................................................................................9 Rate calculation.................................................................................................................12 Results..................................................................................................................................14 Discussion ............................................................................................................................14 Data analysis.....................................................................................................................19 Comparison with other rates..............................................................................................27 Application of data............................................................................................................ 27 Conclusions ..........................................................................................................................31 Acknowledgements...............................................................................................................32 References ............................................................................................................................32 Appendix 1: Data from all Successful Experiments..............................................................38 Appendix 2: Pitzer Equations...............................................................................................43 Chapter 3 : Efflorescent iron sulfate minerals: Paragenesis, relative stability, and environmental impact................................46 Abstract ................................................................................................................................46 Introduction ..........................................................................................................................47 Name and Abbreviation ....................................................................................................49 Methods................................................................................................................................54 Field Methods ...................................................................................................................54