Removal of U(VI) from Aquatic Systems, Using Winery By-Products as Biosorbents: Equilibrium, Kinetic, and Speciation Studies

Grape stalks, a low-cost agro-industrial by-product, were used for the first time as a biosorbent for the removal of uranium from aquatic systems. Basic operating conditions (effect of pH, biosorbent dose, uranium initial concentration, and kinetics) were investigated, and the sorption mechanism was explored. The proposed biosorbent’s efficiency to sequester uranium from different profile aquatic systems was assessed, as well as the potential uranium recovery. Biosoprtion performance increased progressively from pH 1.5 to 4.5, and uranium uptake was a rapid process, where film diffusion was the determining step. Maximum uptake ranged from 90 to 115 mg U(VI) g−1 at 15–33 °C, respectively. None of the commonly used adsorption models (Langmuir, Freundlich, Dubinin-Radushkevich) was able to describe the experimental isotherms, whereas the linear model seems to provide the best fit. Kinetic and thermodynamic data implied that both physical and chemical sorption are involved in the process. Species calculation experiments showed that only positively charged and uncharged uranium species can be retained on the biomass. Quantitative uranium recovery was achieved by mild desorbing agents at concentrations as low as 0.1 M. Therefore, grape stalks seem to be a promising biosorbent due to their high sequestration capacity even under high salinity and acidity conditions, low cost, and easy regeneration.