Effects of pH on Bentonite-Humic Acid Flocculation

Polymer flocculation is commonly utilized to remove colloidal particulates in solution. Flocculation (floc) performance depends on several solution properties such as pH, ionic strength, and natural organic material (NOM) content. Traditional flocculation experiments, known as jar tests, were conducted at pH levels of 3 to 11 and a range of polymer dosages to determine the flocculation efficiency by measuring turbidity. Fluorescently-tagged polymer flocs were imaged with laser confocal microscopy to determine internal floc structure. Not only does bentonite aggregate morphology change as a function of pH, but also humic acid charge density changes, which impacts the flocculation behavior. Flocculation performance of the bentonite-humic acid system differs strikingly from a bentonite only system described in previous works. Competitive flocculation of bentonite and humic acid decreases flocculation performance with increasing solution pH.