The oxidation of pyritic shale under different experimental conditions was studied using an isothermal batch reactor technique. Four pyritic shale samples collected from different areas of an iron ore mine with different stratigraphic compositions in Western Australia were employed in this study. The influence of shale properties on the oxidation of pyritic shale was studied. It was found that the reaction rate constant k (L kg(-1) h(-1)) of the shale oxidation as measured with the present isothermal reactor technique on a per unit pyrite mass basis, was not constant for the different shales and was dependent on their physical properties, where increasing grain size and increasing encapsulation of pyrite grains both result in decreased surface exposure of pyrite to oxidation (per unit mass) which coincides with a decrease in the oxidation rate of pyritic shale (per unit mass). This study demonstrates that pyrite grain size and encapsulation are important parameters for the interpretation and evaluation of acid mine drainage potential associated with individual shales. (C) 2009 Elsevier Ltd. All rights reserved.