Abstract
The sedimentation rate is increased by aggregation of fine particles by flocculation. In colloidal suspensions, however, the floc formation is not sufficient for efficient sedimentation because the aggregates, even though containing large amounts of colloidal particles, still are very small and light, causing slow sedimentation rates. In colloidal systems, flocculation must be preceded by an initial aggregation step of the colloidal particles, using coagulation by an electrolyte or agglomeration by hydrophobic-association. This article compares the influence of initial aggregation through coagulation with aluminum chloride hexahydrated (IAHAC) and initial aggregation induced by dodecylamine (IADDA) on the flocculation of colloidal titanium dioxide particles (anatase) with a hydrolyzed polyacrylamide (HPAM). The results were evaluated in terms of turbidity and final compaction of the sediment. In both cases, the initial aggregation step provided a significant improvement in flocculation with HPAM. The IADDA generated relatively large flocs, the supernatant presented less turbidity, and the sediment was more compacted than with the flocs formed from IAHAC.
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