Flocculation of quartz by a dual polymer system containing tannic acid and poly(ethylene oxide): Effect of polymer chemistry and hydrodynamic conditions

The flocculation behaviors of quartz using a dual polymer system containing tannic acid (TAN) and poly(ethylene oxide) (PEO) were investigated in this study, with dynamic floc size monitoring by the in-situ focused beam reflectance measurement technique. Variables of concern and their influence on the flocculation process were investigated from both physicochemical and hydrodynamic aspects, including solution pH, TAN/PEO ratio, and shear intensity. Floc structure was characterized using confocal scanning microscopy in suspension as well as freeze-drying-SEM imaging method. It was found that prior addition of TAN significantly increased the flocculation efficiency of quartz by PEO at neutral and alkaline pH, but not in acidic solutions despite that PEO induced the largest floc size at pH 3.1 when used alone. An optimal TAN/PEO ratio of 2 was observed for the best flocculation of quartz under the experimental conditions. Additionally, tannic acid could increase the strength of flocs formed by PEO, and the shear resistance of the flocs increased with increasing TAN/PEO ratio. The dual polymer system also contributed to the re-flocculation of quartz under cycled shear conditions, a phenomenon that was not observed when PEO was used alone. Zeta potential and adsorption density measurements confirmed that the pathway of the dual polymer flocculation was via the initial formation of TAN-PEO associative complexes in solution and then bridging of quartz by the associative complexes. The TAN-PEO associative complexes showed different structures and configurations at different pH, in line with a change in hydrogen bonding, which in turn affected floc structures and properties under turbulent conditions. This study helps to understand the improved flocculation, shear resistance and re-flocculation of fine particles induced by dual polymer system.