Effects of Concentration and Molecular Weight of Polycation on the Precipitation of SiO2 Particles and Humic Acid

Abstract

There are various substances in our water resources that could cause to harmful effects upon human consumption. Suspended solids (e.g. SiO₂ particles) and dissolved organic matters (e.g. humic acid) are two of the common contaminants that significantly affect the water quality. The present work aims to investigate the feasibility of using poly (diallydimethylammonium chloride) (PDDA), a cationic flocculant, to purify water contaminated with SiO₂ particles and humic acid via flocculation and precipitation process. Various concentrations (0.1 ppm – 1000 ppm) and molecular weights of PDDA were tested for their contaminant removal efficiency. Results showed that a mild amount of PDDA (0.1 ppm) is sufficient to completely separate 300 mg/L of SiO₂ particles from its suspension (100 % removal). At this optimum concentration, the effect of PDDA molecular weight on the removal efficiency is rather insignificant. However, excess amount of PDDA reduced the removal efficiency as the PDDA may re-stabilize the SiO₂ particles. The same PDDAs were tested for humic acid removal. In this case, it was found that 10 ppm of PDDA is needed to achieve effective removal of humic acid. Similarly, adding excess amount of PDDA (i.e. > 10 ppm) reduced the humic acid removal efficiency. Worth to highlight that the removal kinetic profiles appear to be vastly different for both SiO₂ and humic acid, owing to the different physical natures of these two contaminants.