Biosorption of U(VI) from Aqueous Solution by Chlorella vulgaris : Equilibrium, Kinetic, and Thermodynamic Studies

Abstract

In this study, the mechanism involved in the removal of U(VI) from aqueous solution by the green unicellular microalgae, Chlorella vulgaris, was examined through a series of batch experiments. The effect of various operation parameters such as solution pH, biomass dose, temperature, and different concentrations of U(VI) on the uptake capacity and removal efficiency of C. vulgaris was evaluated. The adsorption process could be defined well by both the Langmuir and Freundlich isotherms with R2 of 0.99 and 0.97, respectively. The kinetic data were fitted to a pseudo second-order model with the R2 value of 0.99. The thermodynamic equilibrium parameters obtained at different temperatures were used to evaluate the thermodynamic constants, ΔG°, ΔH°, and ΔS°. The negative value of Gibbs free energy, ΔG°, demonstrated the endothermic nature of the biosorption process. The adsorption–desorption cycle results demonstrated that this species of algae can be regenerated using 1 M of HCl. The recovery yield of U(VI) ions was found to be 90%, and the biosorption had good reusability after four consecutive adsorption–desorption cycles. The biosorption of U(VI) was found to be adversely affected also by the presence of Al(III) cations, whereas other ions seemed to have negligible effect on the process. The results suggested that C. vulgaris biomass is suitable as a sorbent materials for recovery and biosorption of U(VI) ions from aqueous solution.