Metal removal through synergic coagulation–flocculation using an optimized chitosan–montmorillonite system

Metal cations were removed from water by coagulation–flocculation of the chitosan–montmorillonite system. Co2+, Ni2+ and Cu2+ were used as probe cations. It was found that both chitosan and montmorillonite contribute to the metal ion removal, when used separately, and that coagulation–flocculation strongly depends on the pH and composition of the liquid medium. When used simultaneously, chitosan and montmorillonite displayed a synergy phenomenon, likely due to interactions between the main parameters. Such interactions were investigated through factorial 33 experimental designs. The results show that the highest cation removal yields can be obtained for optimal (chitosan/Mt-K) weight ratio of ca. 5%, pH 6.8, and concentration of 20–100 ppm of Co2+, Ni2+ and Cu2+, while the lowest residual turbidity is attained at pH 5.4 and a (chitosan/Mt-K) of 0.6%. A chitosan excess with respect to the optimal amount may affect the cation removal yields. The results obtained herein provide valuable data that enable to assert that chitosan/montmorillonite are effective coagulating agents and that the presence of organic matter or of dispersed clays is an essential requirement for the effective removal of the metal cation from wastewaters.