Kinetics of the flocculation of clay particles by polyethylene oxide (PEO)at temperatures above the PEO-water cloud point temperature

The kinetics of the flocculation of clay particles by polyethylene oxide (P EO) (5x10(6) Da) at temperatures above the cloud point temperature of the P EG-water solution were studied. The flee size was monitored by photometric dispersion analysis and laser diffraction. Cloud point temperature (CPT) is defined as the temperature at which the PEG-water system undergoes phase s eparation into a PEG-rich and a PEG-lean phase. The CPT was found to decrea se with increasing electrolyte content and shear rate. Flocculation of clay particles was observed only at temperatures above the CPT. The maximum rat e of flocculation and the equilibrium flee size were affected by PEO concen tration, level of shear and temperature difference from the CPT. By changin g the temperature across the CPT, the flocculation process was found to be completely thermally reversible. Flocs that were broken apart when subjecte d to an excessive amount of shear exhibited poor re-flocculating capability . However, flocs that formed under moderate shear conditions were found to flocculate further when the shear rate was decreased to a lower level. A pr oposed flocculation mechanism which involves a cooperative action of adsorp tion of phase-separated PEO onto the clay particles and entrapment of clay particles into the phase-separated PEO aggregates, was also discussed.