Physico-chemical aspects in flocculation of bentonite suspensions by a cyanobacterial bioflocculant

The biopolymer produced by Anabaenopsis circularis strain PCC 6720 was found to be an effective anionic flocculant for bentonite suspensions. The presence of CaCl2 increased the flocculation efficiency significantly. From adsorption isotherms and zeta-potential measurements, it was concluded that the flocculation process is based on the bridging mechanism. The role of CaCl2 is to increase the initial adsorption of the biopolymer on the bentonite particles. It also decreases the negative electrical charge of the bentonite particles and of the biopolymer molecules. The dominant role of the bioflocculant in the flocculation process is discussed according to the theoretical interaction energy curves.