Fractal dimension of large aggregates under different flocculation conditions

• Published in: The Science of the total environment Vol. 609; pp. 807 - 814
• Main Authors: Moruzzi, Rodrigo B., de Oliveira, André L., da Conceição, Fabiano T., Gregory, John, Campos, Luiza C.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 31.12.2017
• Subjects: Aggregates; Flocculation; Fractal dimension; Shear rate; Fractal dimension; Aggregates; Flocculation; Shear rate
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2017.07.194

The two-dimensional fractal dimension (Df) of large aggregates of kaolin (>540μm) during the shear flocculation process for kaolin solution was investigated using non-intrusive in situ image-based acquisition system. Separate experiments were also carried out for three different sized sub-ranges of large aggregates (0.540–1.125mm; 1.125–1.750mm; 1.750–2.375mm). Digital images were taken at a frequency of 10Hz for 10s for each different pairs of gradients of velocity (Gf) of 20 and 60s−1 and flocculation times of 2; 3; 4; 5; 10; 20; 30; 60; 120 and 180min. For the same conditions, particle size distribution (PSD) was also determined. Under the investigated conditions, the lowest Gf produced the greatest Df (1.69) at a flocculation time of 30min for the whole range of aggregates. Also, the evolution of the longest length of aggregate (l) and Df with time, showed that the dynamic steady-state was reached at different times for each shear rate and l ranges. However, Df varied for each size sub-range (ca. 1.1 to 1.8). Finally, the behavior of the aggregate structure may be understood by the predominance of different aggregation mechanisms such as cluster-cluster for Gf of 60s−1 and particle-cluster for Gf of 20s−1. [Display omitted] •Large aggregates were monitored by means of size and fractal dimension (2D), using a non-intrusive image system.•Size range within large aggregates domain results in different behavior of aggregates over time and shear rates.•Breakage and restructuring play an important role on large aggregates.•Structure behavior of aggregates may be explained by aggregation mechanisms.