William Marsh Rice University Department of Earth Science MS-126 6100 South Main Street Houston TX 77005 Sulfide Dissolution Rates Studied by Vertical Scanning Interferometry: Comparison with and Application to Studies in Laboratory and Natural Setting (Final Technical Report) Andreas Luttge 1 and Rolf S. Arvidson 1 Preamble This report is presented in compliance with and satisfaction of reporting requirements for the Mineral Resources External Program (USGS-MRERP, project award #06HQGR0175). The research described here was completed at the Department of Earth Science at Rice University, and represents the work product of the authors as well as the following Rice University graduate students and postdoctoral research staff: Carter Sturm, Michael Vinson, Li Zhang, and Cornelius Fischer. This work also contains results of collaborative activities between the authors at Rice University and Jordi Cama 2 and M. Pilar Asta 2 . The following publication has resulted from this research: Asta MP, Cama J, Solera JM, Arvidson RS and Lüttge A, Interferometric study of pyrite surface reactivity in acidic conditions. Amer. Mineral., in press. Required Statement: “Research supported by the U.S. Geological Survey (USGS), Department of the Interior, under USGS award number #06HQGR0175. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government.” Introduction The effects of acid mine drainage have been extensively documented in the United States, and has been described as a primary source of surface water contamination and degradation of surface environment quality (United States EPA, 1994). The oxidation and subsequent weathering of sulfide minerals releases metals, sulfur, and acid to the surrounding aqueous environment, resulting in contamination and despoiling of surface and ground waters, soils, and sediments, and bioaccumulation of metals in wildlife and domestic stock. In addition to field characterization, there has also been considerable effort devoted to investigation of reaction mechanism, with common dependencies on oxygen concentration, pH, and Fe III (Smith and Shumate, 1970; Singer and Stumm, 1970; McKibben, 1984; McKibben and Barnes, 1986; Nicholson et al., 1988; Moses and Herman, 1991; Williamson and Rimstidt, 1994; Rimstidt and Vaughn, 2003). Reaction mechanism, pH, and oxygen – It is critical to recognize that the dissolution of pyrite often occurs in association with the dissolution of other base metal sulfides as well (Rimstidt et al., 1994). The dissolution of these phases may proceed via a range of possible reactions, including simple non-oxidative hydrolysis, or oxidation by either oxygen or ferric iron. This diversity in reaction paths may lead to parallel or coupled processes, whose interaction produce complex feedback effects that determine the behavior of 1 Department of Earth Science MS-126, Rice University, Houston Texas USA 77005 2 Department of Environmental Geology, Institute of Earth Sciences “Jaume Almera”, CSIC, Lluís Solé i Sabarís s/n, 08028, Barcelona, Catalonia, EU