1:25pm - 1:50pm
The Relationships Between Negative Pore-water Potential, Water Content, Relative Humidity and Sulfide Oxidation in Waste Rock -- a Case Study
1National Research Council Canada; 2Minesite Drainage Assessment Group; 3O’Kane Conultants Inc.; 4Bureau Veritas
Acid rock drainage from mine waste is caused by the oxidation of sulfide minerals in moisture and air. In a test column filled with waste rock, oxidation was measured by oxygen consumption, moisture by weight, and negative pore-water potential indirectly by relative humidity. The results show an interesting correlation between the three.
In waste rock piles, moisture can reach areas not accessed by seepage of meteoric or ground water through vapour transport. Rocks retain/release moisture based on their water retention characteristics. This will in turn influence the relative humidity of the surrounding air space and sulfide oxidation rate.
1:50pm - 2:15pm
Numerical Modelling of Transient Groundwater Flow and Contaminant Transport at the Myra Falls Mine Site
1Robertson GeoConsultants Inc. (RGC), Canada; 2Nyrstar Myra Falls, Campbell River, Canada
The Myra Falls mine is an underground lead-zinc mine on Vancouver Island, British Columbia, Canada. The mine site has been operated since the 1970s and is affected by Acid Rock Drainage (ARD) generated by sulphide-bearing waste rock in the historic waste rock dumps. A numerical groundwater flow and transport model was developed using the software MODFLOW/MT3D to simulate the movement of groundwater and the transport of zinc in the Myra Valley Aquifer (MVA) and to predict Zn loads to Myra Creek during an emergency shutdown of the site-wide SIS.
2:15pm - 2:40pm
Quantification of Environmental Risk of U and Th in Witwatersrand Gold-Mine Tailings, South Africa
Univeristy of the Free State, South Africa
This study explores the most likely mineral hosts and geochemical behaviour of U and Th in Witwatersrand gold tailings facilities with the purpose of quantifying environmental risk. U occurs in the mineral uraninite of which the dissolution is enhanced by the oxidation of pyrite, primarily in the oxidation zone of the tailings facility. U concentrations in tailings pore water may be controlled by secondary U-mineral phases in the tailings zones below the oxidation zone. Th is shown to be insoluble and the phase in which it occurs to be irrelevant in terms of environmental risk of Th leaching.
2:40pm - 3:05pm
A Multicomponent Reactive Transport Modeling Toolbox for Prediction of Drainage Quality from Mine Waste Facilities
1Water Management Solutions, Geological Survey of Finland, Finland; 2Circular Economy Solutions, Geological Survey of Finland, Finland
This study presents a new multiphase multicomponent mine-waste simulator, which is capable of capturing variably saturated water flow, multicomponent advective-dispersive transport both in aqueous and gaseous phase, and chemical reactions (solved with PHREEQC, utilizing PhreeqcRM module) including thermodynamic databases. We particularly emphasize on the Nernst-Planck and Maxwell-Stefan based formulations for the aqueous and gaseous transport, respectively, to explicitly resolve the multilevel process coupling, driven by solute/surface charge or gaseous pressure, across and within different phases. This framework radically goes beyond the state-of-the-art of classical mine-waste models, which exclusively rely on Fickian transport and capture only a subset of governing processes.