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. Nannochloropsis oculata biomass was used for Pb 2+ and Cd 2+ 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 Pb 2+ and Cd 2+ were 1087.20 ± 9.12 mg g −1 and 934.44 ± 12.84 mg g −1 , respectively. The pH for the highest biosorption of Pb 2+ was 5.0, and it was 4.0 for Cd 2+ . The optimal amount of biomass needed to remove 100 ppm Pb 2+ was 0.05 g, and it was 0.3 g for 100 ppm Cd 2+ , which suggests that microalgae showed greater capacity for removal of Pb 2+ than Cd 2+ . The sorption rates for Cd 2+ and Pb 2+ were fitted with the pseudo-second-order kinetic model, and q e values of 94.33 mg g −1 and 88.49 mg g −1 , respectively, were obtained. Cd 2+ reached equilibrium in the medium faster than Pb 2+ . The mechanism for adsorption of Pb 2+ and Cd 2+ is not controlled by intraparticular or film diffusion. FTIR results showed that Pb 2+ and Cd 2+ occupy the same carboxyl, amide, and hydroxyl functional groups. Highlights Lead was adsorbed at higher pH than cadmium . Cadmium and lead were adsorbed in the same functional groups . A loss in adsorption efficiency phenomenon was produced with increasing biomass of N. oculata concentration . The pseudo-second-order kinetic model best described lead and cadmium removal . Chemical adsorption was the rate-controlling step on lead and cadmium sorption .