Acid Rock Drainage (ARD) can be generated by mine waste landforms, for example, waste rock dumps and tailings storage facilities. Closure costs related to the management of ARD can be significant and may last for many years. These liabilities can be reduced by addressing a root cause of the problem at the time of landform construction: oxygen supply to the reactive sulfide minerals.
Oxygen is transported from the atmosphere to the interior of landforms by gas advection and oxygen diffusion. The landform material properties that control the rates of these processes are intrinsic permeability and oxygen diffusion coefficient, respectively.
Rates of consumption of oxygen are determined by material properties such as sulfide sulfur content. Because the oxidation reaction generates heat, temperature changes and the peak temperatures in a landform depend on oxidation rates.
SRK has developed a suite of measurement tools that can be used at mine waste landforms to characterise the rates of oxygen supply (including permeability and oxygen flux meters), rates of oxygen consumption (oxidation rate meter) and oxygen and temperature distributions within the landform.
Changes to landform geometry, waste dump lift heights, and waste compaction to lower intrinsic permeabilities can all reduce oxygen supply. Numerical modelling can be used to guide designs. Measured parameter values are used as inputs to numerical modelling to aid landform design and to confirm that parameter values used at the design stage are achieved in practice.
Numerical modelling provides a means of estimating acid and sulfate generation rates for specific locations within a waste landform and the landform as a whole. These rates can then be used to forecast the water quality of the seepage from the landform.
