Flocculation of aqueous kaolin suspension using a biodegradable flocculant system of poly (vinyl alcohol)-Acacia nilotica gum blends

Acacia nilotica gum (NG) was blended with high hydrolyzed grade biodegradable poly (vinyl alcohol) (Mn¯ 14,000) in different mass proportions to produce a green and efficient flocculant for separartion of a low concentration of kaolin particles (3 mass%) from its suspension. Flocculation efficacy (settling time and turbidity number) was optimized with respect to flocculant dose, PVA-NG blend composition and pH of the medium. Results showed that PVA-NG73 (70% PVA and 30% NG) was the best performing flocculant at 25 ppm dose when the pH of the medium was maintained at 2.6. Zeta potential (both before and after addition of flocculant), hydrodynamic size, isoelectric point and reduced viscosity number were measured to explain the sedimentation rate and turbidity numbers. The floc size was measured and was found to be comparative to the rate of sedimentation. The amount of water absorbed and lost during operation was found to be proportional with the floc size. Impact of inorganic salts on sedimentation was investigated at a neutral pH which showed a faster settling potential of both bivalent and trivalent salts at an optimized concentration (0.3 M), at the best flocculant dose (25 ppm).