Spectroscopic and Modeling Investigation of Eu(III)/U(VI) Sorption on Nanomagnetite from Aqueous Solutions

Nanomagnetite was synthesized by heating natural siderite in nitrogen conditions and was characterized using XRD, XPS, TEM, FT-IR and acid-base titration. Characteristic results illustrated that the reactive site density (17.91 sites/nm²) of nanomagnetite was significantly higher than that of natural siderite (3.63 sites/nm²), whereas average pore size (14.9 nm) of nanomagnetite decreased compared to natural siderite (52.5 nm). Effects of different ambient conditions (i.e., pH, contact time, temperatures and ionic strength) on removal behaviors of Eu(III)/U(VI) on nanomagnetite were conducted by batch experiments. Removal isotherms and kinetics of Eu(III)/U(VI) on nanomagnetite fitted well by models of Langmuir and pseudo-second kinetic, respectively. Additionally, the max sorption capacity of nanomagnetite with Eu(III) (11.95 mg/g) at pH = 2.5 and T = 328 K was significantly higher than sorption capacity of U(VI) (4.93 mg/g). The XPS analysis demonstrated that the surface oxygen groups of nanomagnetite played an important role in the sorption process of Eu(III)/U(VI) via inner surface complexation. The sorption of Eu(III)/U(VI) on nanomagnetite fitted satisfactorily using surface complexation modeling with two and three inner-sphere surface complexation sites, respectively. These findings are crucial for the evaluation of radioactive nuclides at ultralow pH conditions.