Flocculation of kaolinite clay suspensions using a temperature‐sensitive polymer

Abstract A temperature‐sensitive polymer, poly(N‐isopropylacrylamide) [poly(NIPAM)], was tested to flocculate kaolinite clay suspensions. Settling tests at both room temperature and 40°C were carried out. The results show that settling at 40°C resulted in significantly higher settling rates and smaller sediment volumes. This behavior indicates that the polymer molecules changed from a stretched structure to a coil‐like conformation with increasing temperature. It is the change in conformation that induced more compacted flocs, thus resulting in faster settling. To understand the role of temperature in the flocculation, the long‐range interaction and adhesion forces between kaolinite clay particles in the polymer solutions at both room temperature and 40°C were measured using an atomic force microscope (AFM). The measured adhesion forces correlated well with the settling characteristics: a stronger adhesion led to a higher initial settling rate. The retraction force profiles obtained at different temperatures confirmed the conformational change of the polymer with temperature. © 2006 American Institute of Chemical Engineers AIChE J, 2007.