Flocculation of bentonite suspensions with cationic guar

Abstract

Cationic guar gums of varying molar mass and charge density were synthesized and tested as flocculants for bentonite suspensions. The gums were fragmented using ammonium persulphate as a degrading agent, followed by precipitation of the products with ethanol. Cationic charge was added to the guar molecule by reacting it with 2,3-epoxypropyltrimethylammonium chloride. Flocculant performance was assessed by determining the extent of polymer adsorption, by measuring both residual turbidities of the resulting supernatants and the changes in the particles' electrophoretic mobility (EM). Increasing the flocculant charge density causes the optimal flocculation concentration (OFC), as well as the efficient flocculant concentration range, to be reduced. Above this range restabilization occurs. The OFC (for highly modified guar) is also the concentration at which the particles' EM is zero. It was found that decreasing the molecular weight of the guar (at the same charge density) increases the OFC and decreases the electrophoretic mobility of the clay particles in the overdose range.