British Columbia Mine Reclamation Symposium

Rates of sulfide oxidation in submerged environments : implications for subaqueous disposal Morin, Kevin A. (Kevin Andrew), 1955-


The placement of sulfide-bearing tailings and rock in submerged environments has long been recognized as a primary technique for control of acid drainage, and recent field investigations provide further evidence of its success. However, subaqueous disposal does not automatically ensure that acid generation is completely halted. In fact, there are reasons why acid generation might not cease in a submerged environment. Recent experimental data from a generic experiment and from the proposed Cinola Gold Project are reviewed to (1) obtain rates of pyrite oxidation under submerged conditions and (2) show that ferric iron apparently does not oxidize pyrite in the absence of dissolved oxygen. The rates are then used to estimate consumption of dissolved oxygen along groundwater flowpaths and to determine a first-order-rate relationship between reaction rate and dissolved oxygen for calculations of dissolved-oxygen diffusion. Three relatively simple examples show how to apply the concepts and equations. One example for oxygen diffusion shows that, for constant values of porosity and pyrite content, tailings will generate more acidity than coarse rock because of the steeper oxygen gradients within the tailings. The major conclusions drawn from this work are that site-specific conditions dominate in determining the eventual water chemistry and that environmental (hydrogeological) conditions of the disposal site should be well defined. In this way, the site-specific rates and concentrations can be determined and, if necessary, details of the subaqueous disposal can be refined for optimum performance.

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