Biosorption of Cd(II) and Zn(II) by Nostoc commune: Isotherm and Kinetics Studies

In this study, Nostoc commune (cyanobacterium) was used as an inexpensive and efficient biosorbent for Cd(II) and Zn(II) removal from aqueous solutions. The effect of various physicochemical factors on Cd(II) and Zn(II) biosorption such as pH 2.0-7.0, initial metal concentration 0.0-300mg/L and contact time 0-120min were studied. Optimum pH for removal of Cd(II) and Zn(II) was 6.0, while the contact time was 30min at room temperature. The nature of biosorbent and metal ion interaction was evaluated by infrared (IR) technique. IR analysis of bacterial biomass revealed the presence of amino, carboxyl, hydroxyl, and carbonyl groups, which are responsible for biosorption of Cd(II) and Zn (II). The maximum biosorption capacities for Cd(II) and Zn(II) biosorption by N. commune calculated from Langmuir biosorption isotherm were 126.32 and 115.41mg/g, respectively. The biosorption isotherm for two biosorbents fitted well with Freundlich isotherm than Langmuir model with correlation coefficient (r ²<0.99). The biosorption kinetic data were fitted well with the pseudo-second-order kinetic model. Thus, this study indicated that the N. commune is an efficient biosorbent for the removal of Cd(II) and Zn(II) from aqueous solutions. This study shows that the dried biomass of N. commune could be used as an effective and low cost biosorbent for cadmium and zinc ions removal. The biosorption processes are strongly affected by parameters as initial concentration, pH, and contact time and the biosorption kinetic data fitted well with the pseudo-second-order kinetic model.