U(VI) adsorption by biochar fiber–MnO2 composites

The removal of U(VI) by biochar fibers from aqueous solutions has been investigated prior and after MnO₂ surface-deposition. The removal efficiency has been studied as a function of pH, U(VI) concentration, ionic strength, temperature and contact time. The fibers morphology and surface complexes were analyzed by SEM–EDX and FTIR, respectively. Evaluation of the experimental data indicates that the composite presents extraordinary adsorption capacity (q_max = 3.8 mmol g⁻¹, 904 mg g⁻¹), which is attributed to the formation of inner-sphere surface complexes, and that the adsorption reaction is a relatively fast, endothermic and entropy-driven process.