Reversibility of al-kaolin and al-humic aggregates monitored by stable diameter and size distribution
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The reversibility of aggregates during flocculation was investigated. The stable diameter (d) and the power law slope coefficient of the particle size distribution (β) were applied to follow re-formation after breakage. A non-intrusive image-based technique was used for monitoring flocs. Aggregates were formed by adding alum [Al 2 (SO 4 ) 3 ·18H 2 O] by the sweep-coagulation mechanism to two synthetic waters, prepared from kaolin (Fluka) and humic acid (Aldrich Chemical). Velocity gradients (G) varied from 20 to 120 s -1 during experiments, and the rupture occurred under controlled conditions. After rupture, the initial condition was reinstated and reversibility analyzed. Results pointed out the irreversibility of breakage for both Al-kaolin and Al-humic flocs. The stable diameter of aggregates after breakage (d 2 ) varied from 157 to 132 µm for Al-humic and from 233 to 123µm for Al-kaolin aggregates, using G from 20 to 120 s -1 . β 2 values varied from 1.2 to 4.6 for Al-humic and from 0.6 to 7.7 for Al-kaolin.