Erosion and resuspension of cohesive mine tailings.

摘要

The use of shallow water covers for containing sulphide bearing mine tailings in non-arid climates has gained importance over the years due largely to the low diffusivity and solubility of oxygen in water, 2 x 10 -9 m2 s-1 and 8.6 g m -3 at 25°C compared to that in air of 1.78 x 10 -5 and 285 g m-3. As oxygen is one of the key factors in the oxidation of reactive iron bearing sulphide minerals present in the tailings, water covers provide an effective control measure. For water covers to be effective there should be no stirring or resuspension of the bed tailings. However, this seldom happens, as there are many variables in the field that would contribute to the resuspension of tailings. These variables include water level fluctuations and water circulation, and duration and velocity of winds, fetch (the distance along the pond over which wind blows from a certain direction), wave characteristics, sediment compaction and cohesion, and topography of the area.; In this thesis, based on information from eleven mine tailings sites in Canada, Scandinavia and elsewhere existing gaps in shallow water cover design including the problems of wind-induced erosion and resuspension of bottom tailings and cohesive nature of mine tailings were highlighted. Measurements of wind velocity and wave heights at two mine tailings sites in New Brunswick and Ontario, Canada, were conducted. The calculated bottom shear stresses using measured wave height exceeded the critical shear stress for erosion of bottom tailings at wind speeds higher than 9 ms-1. Sediment traps data at the two sites confirmed that resuspension was not a function of depth and wind generated stresses alone, but depended on other factors (for example, cohesion of tailings particles). An Erosion-Transportation-Accumulation (ETA) diagram was then used to confirm the areas of erosion, transportation and accumulation at these sites.; For the first time, the concept of cohesive sediment erosion and resuspension was applied to sulphide mine tailings.; The pH in the reactor tank dropped from neutral to 3.5 over sixteen months while that of the control tank fluctuated about neutral. The electrical conductivity of the water cover in the reactor tank was 2800 muS.cm-1 compared to 1600 muS.cm-1 in the control tank at the end of the experiments. Similarly, calcium, sulphate, manganese, and ferrous iron concentrations in the reactor tank were 600, 1730, 33, and 26.4 mgL -1 respectively compared to the corresponding values of 400, 860, 6.85 and 0.09 mgL-1 in the control tank. (Abstract shortened by UMI.)