Fractal analysis of mineral aggregates via in-situ imaging: Bridging flocculation under high shear conditions

The key challenge in selective flocculation is the presence of gangue particles in the aggregate product, due to imperfect chemical selectivity or physical entrapment. This extends to selective flocculation-flotation, where the aggregates experience a continuous shear environment during flotation. As a first step towards understanding how aggregate shape and structure impacts selective flocculation-flotation, this study seeks to estimate the fractal properties of aggregates (30–250 µm) formed from particles (1–20 µm) under flotation shear conditions > 1000 s −1 . This was conducted via image processing following in-situ microscopy of aggregates in chalcopyrite, hematite, and mixed hematite-quartz systems, to estimate the 2D area fractal dimensions (D 2 ) based on box-counting and length-area methods. All aggregates characterised were relatively compact with D 2 ranging between 1.6 and 1.95. Aggregates of higher D 2 – associated with more compact aggregates – were produced at lower shear and mixing time, in contrast to literature observations at lower shear rates. This was attributed to shear breakage being a dominant mechanism over densification. D 2 increased with increasing flocculant molecular weight and dose, potentially due to higher resistance to breakage. In mixed mineral systems, aggregates were more fractal with the use of a dispersant, potentially due to improved flocculation efficiency for the targeted minerals.