Insights into the long-term immobilization performances and mechanisms of CMC-Fe0/FeS with different sulfur sources for uranium under anoxic and oxic aging

Abstract

Nanoscale zerovalent iron (Fe⁰)-based materials have been demonstrated to be a effective method for the U(VI) removal. However, limited research has been conducted on the long-term immobilization efficiency and mechanism of Fe⁰-based materials for U(VI), which are essential for achieving safe handling and disposal of U(VI) on a large scale. In this study, the prepared carboxymethyl cellulose (CMC) and sulfurization dual stabilized Fe⁰ (CMC-Fe⁰/FeS) exhibited excellent long-term immobilization performances for U(VI) under both anoxic and oxic conditions, with the immobilization efficiencies were respectively reached over 98.0 % and 94.8 % after 180 days of aging. Most importantly, different from the immobilization mechanisms of the fresh CMC-Fe⁰/FeS for U(VI) (the adsorption effect of -COOH and -OH groups, coordination effect with sulfur species, as well as reduction effect of Fe⁰), the re-mobilized U(VI) were finally re-immobilized by the formed FeOOH and Fe₃O₄ on the aged CMC-Fe⁰/FeS. Under anoxic conditions, more Fe₃O₄ was produced, which may be the main reason for the long-term immobilization U(VI). Under oxic conditions, the production of Fe₃O₄ and FeOOH were relatively high, which both played significant roles in re-immobilizing U(VI) through surface complexation, reduction and incorporation effects.

Keywords: Fe(3)O(4); FeOOH; Long-term stability mechanisms; Nanoscale zerovalent iron; Re-immobilization; U(VI).