Enhanced uptake capacity for uranium(VI) in aqueous solutions by activated natural siderite: Performance and mechanism

Abstract Siderite as a Fe(II)-bearing mineral often be naturally weathered and oxidized into goethite, which would decrease the surface chemical activity of the siderite. The chemical activity of siderite is improved by decomposing weathering-formed goethite at low temperature (350 °C). The activated natural siderite (ANS) was utilized to remove U(VI) from aqueous solutions. Batch experiments revealed that ANS after thermal treatment at 350 °C (ANS350) exhibited excellent uptake performance toward U(VI) (14.65 mg/g) which was better than natural siderite (9.00 mg/g) at pH = 4.0 and T = 293 K. Meanwhile, the uptake percents of U(VI) on NS and the uptake process was involved electrostatic attraction on the surface of adsorbents. The characterization results illustrated that activated natural siderite at 350 °C presented the better uptake capacity due to its larger specific surface area and smaller average pore size compared to natural siderite, which was optimized to adsorb U(VI) from aqueous solutions. The spectroscopic analysis demonstrated that the abundant surface oxygenated functional groups of ANS facilitated the uptake process of U(VI). Meanwhile, reduction was also involved in the process. Additionally, the U(VI) reduction amount can be enhanced to some extent after calcination. These findings give insight into the further development of activated natural mineral obtained by heating in low temperature, for using as potential candidate in immobilization of uranium(VI) from contamination water in actual environmental management.