Impact of hydrodynamic conditions on the structure of clay-based tailings aggregates flocculated in freshwater and seawater

The impact of shear rate on the structural properties of aggregates obtained during the flocculation of clay-based tailings with an anionic polyacrylamide was analyzed. The effects generated in industrial water (IW) and seawater (SW) were compared. Flocculation-sedimentation batch tests were performed to know aggregate size distribution, hindered settling rate, and internal structure of flocs expressed through their fractal dimension. The aggregate properties were characterized by the Focused Beam Reflectance Measurement (FBRM) and Particle Vision Microscope (PVM) techniques. The aggregate size distribution showed a bimodal behavior, where a portion of the particles does not flocculate properly unless the shear rate increases during flocculation. On the other hand, the size and quantity of coarse aggregates strongly depend on the mixing intensity. The use of seawater led to a reduction in the size of aggregates. It is suggested that this is a result of polymer coiling, which leads to a decreased ability to form polymeric bridges and thus less particle capture. The fractal dimension of aggregates shows that while the shear rate increases, the aggregates are less compact, with structures possibly more open and further away from a solid spherical body. The greatest reduction occurred in industrial water, related to the larger size of the structures in a low salinity environment.