Effects of low temperature oncoagulation of kaolinite suspensions

Water Research 42 (12), 2983-2992

Link: http://www.sciencedirect.com/science/article/pii/S004313540800153X

In this study, coagulation of kaolinite suspensions at low temperatures is comparedwith that at an ambient temperature of 22 °C, and the process is examined with regard to the coagulation rate (CR) and chemical aspects of coagulation. Experiments using a photometric dispersion analyzer (PDA) show that coagulationof kaolinite suspensions can be taken as a two-phase process. Low temperature greatly reduces the CR of the first phase but not that of the second one. On the other hand, results show that low temperature did not serve to impede the hydrolysis of aluminum [Al(III)] within 1 min of alum addition. Themeasurements of electrophoretic mobility (EM) indicate that destabilization of kaolinite particles by hydrolyzed Al species was not hindered by low temperature within 1 min of alum addition. Slow coagulation at low temperatureis due to the lowered CR but not the altered chemistry aspect of Al(III). Furthermore, the change in settled turbidity after 20-min flocculation as a function of coagulant dosage was more severe in the cold because of the low CR. Elongating floc-growth time, as observed, was able to counterbalance the retarded CR at low temperature and improve turbidity removal efficiency.