Biosorption of U(VI) from aqueous systems by malt spent rootlets. Kinetic, equilibrium and speciation studies

A low-cost and environmentally friendly cleanup technique is evaluated in this study, based on the use of a brewery by-product, malt spent rootlets, as potential biosorbent for U(VI) sequestration from aquatic systems. Uranium uptake was rapid (2.5 h at 25 °C), and MSR exhibited capability of removing U(VI) from effluents of high acidity (pH 1.5) and salinity (0.5 M NaCl and NaNO3). Maximum uptake was 157 mg U(VI) g-1 at 25 °C. The pseudo-second-order model gave the best fit for kinetic data, whereas film diffusion was the rate-controlling step. Langmuir adsorption isotherm was the best fitting model. Activation energy, thermodynamic data and the extent of sorption reversibility implied that sorption of U(VI) is predominantly chemical. FTIR studies showed that lignin moieties are mainly responsible for U(VI) uptake. Speciation modeling showed that only positively charged and uncharged uranium species can be retained on the biomass. Finally, desorption studies revealed that Na2CO3 was the most efficient eluent with 78 % of U(VI), previously bound on the biosorbent's surface, recovered.