Modification of chitosan with carbamoyl benzoic acids for testing its coagulant-flocculant and binding capacities in removal of metallic ions typically contained in plating wastewater

This paper proposes the use chitosan modified with carbamoyl benzoic acids as new coagulant-flocculant agents for metals removal from aqueous solutions. The grafted chitosan species as chitosan dianhydride (ChD) and chitosan dianhydride-amine (ChDA) improved the removal of Cu2+, Pb2+, Ca2+, Cr3+, Zn2+ and Ni2+, compared with chitosan alone. Zeta potential measurements predict doses and allowed to calculate binding constants between the new coagulant-flocculant agents and metallic cations (from 104 to 105 M−1). After the coagulation-flocculation, solids were analyzed by SEM and EDS. SEM images show the texture of solids depending on the functional group grafted on chitosan. EDS study of solids containing chitosan dianhydride-metals (average of all scanner areas) revealed the wt% of metals: Cr (10.45%), Cu (5.95%), Ni (5.22%), Zn (4.36%), Pb (1.37%), Cd (0.31%) and Ca (0.10%) For recovered solids containing chitosan dianhydride-amine-metals, the observed wt% appeared in the same order: Cr (12.44%), Cu (6.75%), Ni (5.75%), Zn (5.12%), Pb (1.82%), Cd (0.59%) and Ca (0.12%).