Exploring polyelectrolytic features of the exudate from native Acacia nilotica for flocculating aqueous kaolin suspension

The air dried exudate of native Acacia nilotica, referred as natural gum or NG in this article, has been purified and characterized for using it as a local, bio-based flocculant for kaolin suspension. Results show that NG is a carbohydrate of nearly 25% purity out of which 7% is the reducing sugar and the rest 75% is natural silica present as contaminant. The macromolecule contains COOH units. This along with OH units impart polyelectrolytic character for which the molecules interact with SiOH units of kaolin and settles the suspension. The settling data shows that 25 ppm is the best flocculant dose in respect of fastest settling and lowest residual turbidity for settling a 3 wt% suspension. Investigation on pH shows that 1.6-2.6 is the best working range, however, in the high stability zone (low acidity to strong basicity), the results are satisfactory. Due to high average floc size and low effective density of the flocs obtained at high acidic condition, the amount of fresh water lost inside the sediment is higher as compared to neutral and basic conditions.