Effect of structure and charge of polysaccharide flocculants on their flocculation performance for bentonite suspensions

How to dewatering of colloidal stable clay suspensions in a low energy consumption and environmentally friendly way is an intractable issue. The present work used guar gum (G, linear polymer) and its two derivatives, nonionic hydroxypropyl guar gum (HG, branched polymer) and cationic hydroxypropyl guar gum (CHG, positively charged branched polymer) as flocculants and bentonite as colloidal particles to find an efficient flocculation system. The flocculation performance was systematically evaluated through standard jar test procedure and laser light scattering measurements. It was found that all the investigated polysaccharides showed high flocculation performance for bentonite suspensions. In all cases, the residual turbidity (RT), optimal polymer dosage and optimal settling time, which are key factors in the flocculation study, are compared to elucidate the impact of the polysaccharides structure (linear or branched) and charge (nonionic or cationic) on the flocculation rate and efficacy. Comparative tests showed that the flocculation rate and flocculation efficacy were influenced strongly by the polysaccharides properties. The flocculation efficacy and rate of branched polymer HG is poorer than that of linear polymer G. But it is worth noting that the ability to catch smaller particles of HG is significantly greater than that of G. In comparison to the two nonionic polymers, the positively charged polymer CHG showed the fastest flocculation rate and the best flocculation efficacy for flocculating negatively-charged bentonite suspensions. Furthermore, it was also found that the additional positive charge of CHG have significantly enhanced its capability to adsorb and capture smaller clay particles as compared with the branched-chain structure of HG.