The effect of chemical and thermal modifications on the biosorption of uranium in aqueous solutions using winery wastes

Abstract

Biosorbents from winery wastes were tested for the removal of U(VI) after chemical and thermal modifications which led to significant improvement of the properties and the sorption capacity of the raw material. Batch experiments in aqueous solutions were undertaken to examine the influence of various parameters (pH, dosage, contact time, temperature, initial concentration, and ionic strength). Isotherms and kinetics obtained at pH3 and 4 (Cinitial:5–300 mgL−1,) were fitted by the Langmuir, Freundlich, pseudo-first- (PFO) and pseudo-second-order (PSO) equations respectively. Characterization techniques (SEM-EDS, XRD, FTIR and XPS) were used to explore the mechanism of U(VI) adsorption which seems to include dipol-cation interactions and formation of surface complexes as well as ion exchange and surface-supported reduction of U(VI) to U(IV), which most probably results in the surface precipitation of the very low soluble U(OH)4. Desorption tests were performed and showed the safe disposal of the loaded sorbents. It was demonstrated that a simple and low-cost chemical modification results in significant improvement of the sorption capacity of the raw material (from 58 to 250 mg g−1) due to presence of functional groups while thermal modification enhances the stability of the material offering lesser improvement (qmax:100 mg g−1)