Biosorption of thorium onto Chlorella Vulgaris microalgae in aqueous media

Thorium biosorption by a green microalga, Chlorella Vulgaris, was studied in a stirred batch reactor to investigate the effect of initial solution pH, metal ion concentration, biomass dosage, contact time, kinetics, equilibrium and thermodynamics of uptake. The green microalgae showed the highest Th adsorption capacity at 45 °C for the solution with a thorium concentration of 350 mg L^-1 and initial pH of 4. The amount of uptake raised from 84 to 104 mg g^-1 as the temperature increased from 15 to 45 °C for an initial metal concentration of 75 mg L^-1 at pH 4. Transformation Infrared Spectroscopy (FTIR) was employed to characterize the vibrational frequency changes for peaks related to surface functional groups. Also, the scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX) were used to determine the morphological changes and elemental analysis of the biosorbent before and after the sorption process. The Langmuir isotherm was in perfect agreement with the equilibrium empirical data of thorium biosorption and the highest sorption capacity of the Chlorella Vulgaris microalgae was determined as 185.19 mg g^-1. Also, the results of kinetic studies show that the thorium biosorption process follows a pseudo-second-order kinetic model. The negative value of ΔG⁰ indicates spontaneity and the positive values of ΔH⁰ indicate the endothermic nature of the adsorption process.