Multiphase transfer processes in waste rock piles producing acid mine drainage 1: Conceptual model and system characterization

Acid mine drainage (AMD) results from the oxidation of sulfides, mainly pyr ite, present in mine wastes, either mill tailings or waste rock. This is th e first of two papers describing the coupled physical processes taking plac e in waste rock piles undergoing AMD production. Since the oxidation of pyr ite involves the consumption of oxygen and the production of heat, the oxid ation process initiates coupled processes of gas transfer by diffusion and convection as well as heat transfer. These processes influence the supply o f oxygen that is required to sustain the oxidation process. This first pape r describes a general conceptual model of the interaction of these coupled transfer processes. This general conceptual model is illustrated by the phy sicochemical conditions observed at two large sites where extensive charact erization programs revealed widely different properties. The South Dump of the Doyon mine in Canada is permeable and has a high pyrite oxidation rate leading to high temperatures (over 65 degreesC), thus making temperature-dr iven air convection the main oxygen supply mechanism. The Nordhalde of the Ronnenberg mining district in Germany contains lower permeability material which is less reactive, thus leading to a more balanced contribution of gas eous diffusion and convection as oxygen supply mechanisms. The field charac terization and monitoring data at these sites were thoroughly analyzed to y ield two coherent sets of representative physical properties. These propert ies are used in the second paper as a basis for a plications of numerical s imulation in AMD-producing waste rock piles. (C) 2001 p Elsevier Science B. V. All rights reserved.