Mechanism of uranium retention via reductive biotite under the aerobic conditions: Role of structural ferrous iron

Abstract

A comprehensive understanding of the environmental fate of uranium necessitates a thorough understanding of the sequestration mechanism of uranium on typical rock-forming minerals. In this work, the sorption behavior and mechanism of uranium on four kinds of biotite with different iron contents were investigated, and the role of structural ferrous iron in uranium sorption was determined with spectroscopic techniques. The results indicated that the interactions of U(VI) with biotite are governed primarily by redox reactions and surface complexation. The reduction in the U(VI) is induced by structural ferrous iron, which accounts for approximately half of the iron content, and an increased iron content in biotite can augment the number of binding and reduction sites available for U(VI). Biotite weathering facilitated U(VI) reduction to UO₂ or hyperstoichiometric uranium oxides, and the amounts of electrons transferred between ferrous iron and the absorbed U(VI) exhibited a linear relationship, which highlights the pivotal role of ferrous iron in uranium sorption. Uranium sorption in anaerobic conditions exceeds aerobic conditions due to improved electron transport and reduction efficiency. These insights are essential for understanding the mechanisms behind uranium retention in biotite-rich granitic terrains and offer valuable perspectives on potential strategies for remediating uranium-contaminated sites.