To understand the plume dispersion and the continuous process of settling, deposition and bed formation of mine tailings in this project, first the tailings are characterized. The analyses results enable narrowing down of uncertainties in the critical sediment parameters in the predicted behaviour of the mine tailings and are the basis of the project to select potential floculants flocculants used in Phase 2 and 3.
1) Collation of typical tailing samples for further laboratory analyses
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During the mining process a plume of material will be placed above the bed . In time the particles within the plume will settle. This hindered settling process is related to time. The higher the settling velocity, the faster the particles reach the bed , the smaller the spread of the plume and chances of spreading of the plume leading to environmental issues. The floculant flocculant will influence this hindered settling velocity. To understand the influence of the floculantflocculant, first the hindered settling of the material without floculant flocculant is tested . This experiment is carried out in 1 m tall settling columns. For each tailings type, two different concentrations are used to resolve the two unknowns; gelling concentration en the maximum settling velocity. These two material properties determine the formation of a bed and settling of an individual particle in still water. The material is posed placed into the columns (well mixed). Thereafter the hindered settling process is recorded with camera's. From this data set the hindered settling velocity can be determined as shown in the graph below. The higher the concentration, the lower the settling velocity because more particles hinder each other. For concentrations larger than 150 g/l, the settling velocity reseaches reaches zero. The particles are close enough to each other to form a (gelled) bed. The maximum fall velocity is determined by the weight of the particle and the surrounding concentration. However it should be taken into account that these are controled controlled laboratory conditions. In the field the plume be exposed to currents or storm conditions enforcing uplift conditions.
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3) Settling and consolidation columns
Set-up consolidation experiments; After 10 minutes of hindered settling phase; After 9 hours: consolidation phase 1
