Flocculation of bentonite particles by a cyanobacterial bioflocculant

Abstract Flocculation of bentonite suspensions by bioflocculant produced by the cyanobacterium Phormidium species strain J1 was correlated with the adsorption mechanism of the flocculant on the bentonite particles in the presence of various CaCl 2 concentrations. The optimal flocculant concentration decreased with an increase in CaCl 2 concentration, and the adsorption increased with the increase in CaCl 2 concentration. Langmuir-type adsorption isotherms were obtained yielding ΔG° ads of - 12 kcal mol −1 , at any CaCl 2 concentration, while the maximum adsorption increased with the increase in CaCl 2 concentration. From measurements of electrophoretic mobility and Ca 2+ uptake by the particles and the flocculant if was concluded that the role of CaCl 2 is to increase the amount of adsorbed flocculant at any given flocculant concentration, thus shifting the optimal flocculant concentration toward lower values.