Estimation of Evaporation and Infiltration from Gold and Platinum Mine Tailings
Lorentz, Simon Antony
In southern Africa the mean annual potential evapotranspiration exceeds the mean annual rainfall, in places by threefold. Actual evaporation from tailings beaches is therefore controlled primarily by the hydraulic fluxes in the tailings upper surfaces and comprises a critical component in the water balance. The rates of actual evaporation loss are often assigned to an empirical factor over the entire beach area, leading to erroneous water balance fluxes, particularly where the evaporation driving gradients are high, as in the semi-arid areas of southern Africa. This compounds the management of an already scares water resource in these climates. In this study, a series of large columns (300 mm diameter by 1500 mm long) were set up in a subsurface compartment, such that the sample top surfaces were level with the adjacent ground surface. Materials included tailings from gold, copper, platinum and mineral sand mines. The columns were insulated and instrumented with soil water tension (mini tensiometers), soil water content (Time Domain Reflectometry) and water level sensors. The samples were initially fully saturated and observations made through the drying cycle. Periodic stable isotope water and vapour samples were extracted from the interior in surface of the columns. Evaporation rates were high initially (>6 mm/day), reduced rapidly within one week of drying, but continued gradual water loss over a second week. Simulation of the observed water and vapour fluxes allow for direct insight into the evaporation component in Tailings Storage Facility water balance analyses.