Kinetic Modeling of Cd(II) and Pb(II) Biosorption from Aqueous Solution by Inactive Biomass of Nannochloropsisoculata Microalgae

The development of heavy metal treatment technologies plays a crucial role in avoiding contamination of water bodies. Nannochloropsisoculata biomass was used for Pb2+ and Cd2+ biosorption. The biosorption capacity (g metal × g biomass−1) was determined by evaluating the effects of pH and biomass amount. The maximum biosorption capacities for Pb2+ and Cd2+ were 1087.20 ± 9.12 mg g−1 and 934.44 ± 12.84 mg g−1, respectively. The pH for the highest biosorption of Pb2+ was 5.0, and it was 4.0 for Cd2+. The optimal amount of biomass needed to remove 100 ppm Pb2+ was 0.05 g, and it was 0.3 g for 100 ppm Cd2+, which suggests that microalgae showed greater capacity for removal of Pb2+ than Cd2+. The sorption rates for Cd2+ and Pb2+ were fitted with the pseudo-second-order kinetic model, and qe values of 94.33 mg g−1 and 88.49 mg g−1, respectively, were obtained. Cd2+ reached equilibrium in the medium faster than Pb2+. The mechanism for adsorption of Pb2+ and Cd2+ is not controlled by intraparticular or film diffusion. FTIR results showed that Pb2+ and Cd2+ occupy the same carboxyl, amide, and hydroxyl functional groups.