Abstract: Given the potential impact of selenium (Se) on human health and ecosystems, as well as its significance in the study of lepidocrocite transformation mechanisms, we explored the role of hydrated ferrous ions (Fe(Ⅱ)(aq)) in mediating the abiotic catalytic transformation of selenite (Se(Ⅳ))-loaded lepidocrocite (Lp) under neutral anaerobic conditions, and revealed the key roles of initial Fe(Ⅱ) concentration and selenium loading in determining the type of transformation products, phase transition pathways, and their impacts on selenium bioavailability. The results showed that the competitive adsorption between Se(Ⅳ) and Fe(Ⅱ) and the redox reaction between Se(Ⅵ) and Fe(Ⅱ) significantly affected the efficiency of lepidocrocite transformation and the composition of the resulting products. A high Fe(Ⅱ) concentration promoted the transformation of lepidocrocite to goethite, but the presence of Se(Ⅳ) reduced the relative proportion of goethite in the products. Additionally, during this phase in transformation process, there was no significant selenium release in systems with high Fe(Ⅱ) concentrations, while low Fe(Ⅱ) concentrations facilitated the release of small amounts of selenium. These findings are significant for understanding the transformation behavior of lepidocrocite in selenium-containing environments and selenium bioavailability, and provide insights for guiding the remediation of selenium pollution in actual environmental contexts.

Key words: Fe(Ⅱ), Se(Ⅳ), lepidocrocite, reduction, phase transformation