Flocculation of bentonite particles by a cyanobacterial bioflocculant

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 CaCl₂ concentrations. The optimal flocculant concentration decreased with an increase in CaCl₂ concentration, and the adsorption increased with the increase in CaCl₂ concentration. Langmuir-type adsorption isotherms were obtained yielding ΔG°_ads of - 12 kcal mol^-1, at any CaCl₂ concentration, while the maximum adsorption increased with the increase in CaCl₂ concentration. From measurements of electrophoretic mobility and Ca²⁺ uptake by the particles and the flocculant if was concluded that the role of CaCl₂ is to increase the amount of adsorbed flocculant at any given flocculant concentration, thus shifting the optimal flocculant concentration toward lower values.