Kinetic and equilibrium studies on biosorption of cadmium(II) from aqueous solution by Gracilaria corticata and agar extraction algal waste

This study consists of using a new red algal species biomass together with Cd, as a toxic metal from synthetic contaminated wastewaters in order to test biomass potential to become a by-product to be used for the wastewater treatment. The effects of solution pH, initial Cd(II) concentration, biosorbents dosage, and contact time on the removal efficiency of Cd(II) from the synthetic solutions were investigated. Cd(II) sorption was found to be highly pH dependent, and the maximum sorption was obtained at pH 6.0. The removal efficiency of Gracilaria corticata and the agar extraction algal waste increased from 53 to 87% and 62 to 96% for an increase in biomass from 0.1 to 0.5 g L−1, respectively. Equilibrium data follow Langmuir model. The parameters of Langmuir equilibrium model are q max = 226.9 mg g−1, b = 0.009 mg L−1 and q max = 197.4 mg g−1, b = 0.012 mg L−1, respectively, for G. corticata and agar extraction algal waste. Different kinetic models such as pseudo-first-order, pseudo-second-order, and intra-particle diffusion model were tested, and the experimental data were in agreement with the pseudo-second-order model. FT-IR of biomasses revealed that amino, hydroxyl, and carbonyl were main functional groups. The results of SEM–EDX indicate that ion exchange occurred during the adsorption process. The present study suggests that G. corticata and agar extraction algal waste can be used as effective, environmentally friendly, and efficient biosorbents for Cd(II) removal from aqueous solution.