Unveiling the dual role of calcium peroxide in enhancing green rust-catalyzed arsenite oxidation and stabilization

Abstract

Iron oxyhydroxide redox processes coupled with reactive oxygen species (ROS) generation play a critical role in the transformation of arsenic (As). However, low ROS generation limits the detoxification and stabilization of As(III). In this study, we propose a novel strategy by integrating Fe(II) rich green rust (GR) with calcium peroxide (CaO₂) for the efficient transformation of As(III) under oxic conditions. The results demonstrate that the introduction of CaO₂ greatly enhances the oxidation and immobilization of As(III) by GR. Quenching experiments reveal that H₂O₂, ·O₂⁻, and ¹O₂ are the primary ROS responsible for the oxidation of As(III). Importantly, CaO₂ significantly boosts the production of key ROS in the GR/CaO₂ system. Additionally, the introduction of CaO₂ facilitates the transformation of both non-specific and specific adsorbed As into non-extractable As, improving the stability of immobilized As. Our findings unveil that CaO₂ serves a dual role in promoting GR-catalyzed As(III) oxidation and stabilization by enhancing ROS production and forming iron-arsenic-calcium complexes. Moreover, the application of GR/CaO₂ in As-contaminated soil can rapidly reduce the risk of As leaching in different scenarios. Therefore, this study provides a new strategy using CaO₂ coupled with iron redox process to enhance oxidation and stabilization of arsenic in water and soil.