ORIGINAL ARTICLE Comparison of dissolution under oxic acid drainage conditions for eight sedimentary and hydrothermal pyrite samples Ran Liu Æ Amy L. Wolfe Æ David A. Dzombak Æ Brian W. Stewart Æ Rosemary C. Capo Received: 25 August 2007 / Accepted: 19 November 2007 / Published online: 11 December 2007 Ó Springer-Verlag 2007 Abstract The abiotic oxidative dissolution behaviors of eight natural pyrite samples, five sedimentary and three hydrothermal, from various geological environments were compared under oxic conditions at pH 3 and 6 in a highly controlled batch reactor dissolution system. The three sed- imentary pyrite samples associated with coal had greater specific surface areas and also exhibited greater apparent dissolution rates and extent than the other two sedimentary and three hydrothermal samples under both pH conditions. However, after normalizing for surface area, the dissolution rate constants for the different pyrite samples were similar; the greatest difference was between the two non-coal sedi- mentary pyrite samples. Pyrite morphology and the presence of trace metals could contribute to the differences in disso- lution behavior as reflected in the normalized dissolution rates. The sulfur:iron ratio observed in the aqueous solution at pH 3 increased with time, but was always less than 2.0 (predicted from the stoichiometry of dissolution) for all the pyrite samples during the 24-h experimental duration. This can be explained by the disproportionation dissociation of thiosulfate, an initial product of pyrite dissolution, to ele- mental sulfur and sulfate which does not occur in a 1:1 ratio. The results of this work indicate the importance of extracting and using the specific pyrite(s) relevant to particular mining areas in order to understand pyrite dissolution rates and the influence of environmental conditions on those rates. Keywords Pyrite  Sedimentary  Oxidative dissolution  Trace metal contents  Semiconducting properties Introduction Pyrite (FeS 2 ) is the most abundant and widespread sulfide mineral on the surface of Earth. Pyrite can be formed under high temperature conditions, including contact metamor- phism and hydrothermal fluid circulation, as well as in low- temperature sedimentary environments (Berner 1970; Berner 1984; Langmuir 1997). The oxidative dissolution of pyrite is the primary cause for the formation of acid mine drainage (AMD), which has significant impacts on water quality in mining regions across the world. Numerous studies have been undertaken to understand pyrite dissolution chemistry (Singer and Stumm 1970; Biegler and Swift 1979; Lowson 1982; Pugh et al. 1984; McKibben and Barnes 1986; Moses et al. 1987; Moses and Herman 1991; Rimstidt and Newcomb 1993; Williamson and Rimstidt 1994; Evangelou and Zhang 1995; Bonnissel-Gissinger et al. 1998; Holmes and Crundwell 2000; Schoonen et al. 2000; Paschka and Dzombak 2004) in order to improve our ability to describe and predict AMD generation. The rate of pyrite oxidative dissolution has been studied most often by monitoring aqueous phase concentration of Fe 2+ or sulfur species (mainly SO 4 2- ) released in batch reactors during dissolution experiments. Dissolution of pyrite in water is affected by a number of physical, chemical, and biological factors including pH, dissolved oxygen R. Liu  D. A. Dzombak (&) Department of Civil and Environmental Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA e-mail: dzombak@cmu.edu A. L. Wolfe  B. W. Stewart  R. C. Capo Department of Geology and Planetary Science, University of Pittsburgh, Pittsburgh, PA 15260, USA Present Address: R. Liu ARRO Consulting, Inc., 270 Granite Run Drive, Lancaster, PA 17601, USA 123 Environ Geol (2008) 56:171–182 DOI 10.1007/s00254-007-1149-0