Oxygen diffusion in saturated covers

Phase 1: Impacts of Water Table Level on Mine Waste Management Using a Saturated Cover

The mine life cycle, from exploration to mine closure can be fast-paced and volatile, therefore careful consideration should be given to remediation planning of mine sites. This lab-scale study focused on the effects of low vs. high water tables within tailings impoundments, in conjunction with a monolayer cover system, in mitigating AMD production. Tailings and cover material were collected from the Faro Mine site in Faro, Yukon.

Phase 2:

This study focused on oxygen concentration and unfrozen volumetric water content within freezing conditions through a series of laboratory column experiments and through an analysis of diffusion coefficients De and Kr, from Fick's first and second law. In order to create a representative model of freezing conditions for the numerical simulations, large instrumented columns were used with an inert material filling, and the evolution of the following parameters were monitored over time and depth: volumetric water content, unfrozen volumetric water content, temperature; and oxygen concentration gradient between the water interface and the top of the cover material (only the partially water-saturated portion).

Phase 3:

Most, if not all, of the experiments done to map oxygen diffusion in saturated covers with negative temperatures have been done with Fick’s first and second laws of diffusion which require the use of unreliable parameters and complicated variables. Previous experimentation also used equipment that directly consumed or impacted oxygen levels in some way.

Taking this into consideration, it was decided that in order to be able to more accurately predict oxygen diffusion in field scenarios modeling would be used. Modeling is not an uncommon method of predicting diffusion in this setting, however, what made this method unique was the setup of the instrumented columns. The variables that were recorded during this process were temperature, percent oxygen and unfrozen volumetric water content.