A robust prediction of U(VI) sorption on Fe₃O₄/activated carbon composites with surface complexation model

A robust prediction of U(VI) on Fe₃O₄/activated carbon (Fe₃O₄/AC, fabricated by co-precipitation method under N₂ conditions) under different pH was developed via diffuse layer model, in accordance with FI-IR, XRD and XPS analysis. No influence of ionic strength onto U(VI) adsorption by Fe₃O₄/AC under ambient conditions suggested the inner-sphere surface adsorption, which was attributed to abundant surficial functional groups according to FT-IR and XPS analysis. The batch experiments indicated Fe₃O₄/AC with fast adsorption rate (equilibrium within 60 min), high adsorption capacity (56 mg/g at pH 4.0) towards U(VI). The adsorbed U(VI) was partly reduced by Fe²⁺ of Fe₃O₄/AC by XPS analysis. Surface complexation modeling showed that a single set of monodentate and mononuclear species (SOUO₂⁺) cannot predict U(VI) adsorption at high pH, whereas the robust prediction of U(VI) adsorption over wide pH range was observed by adding the other binuclear and tridentate species ((SO)₂UO₂(CO₃)^6-). These findings revealed that magnetic AC as a candidate for immobilization and/or preconcentration of radioactive wastewater in environment management.