Mechanisms of arsenic oxidation in the presence of pyrite: An experimental and theoretical study

The mobility and toxicity of arsenic are significantly influenced by the natural minerals. A comprehensive understanding of the interaction between arsenic and minerals is crucial for elucidating the natural behavior of arsenic and advancing arsenic remediation strategies. In this study, the mechanism of As (III) oxidation in the presence of pyrite without light irritation was investigated by experimental and theoretical approaches. Quenching experiment and electron paramagnetic resonance analysis confirm center dot OH and center dot O2H is the predominant oxidant of As (III) under acidic and alkaline condition, respectively. Density Functional Theory (DFT) calculations indicate on the pyrite surface, the surface oxygen species is insignificant in As(III) oxidation but crucial for the generation of reactive oxygen species (ROS). In the solution, center dot OH, center dot O2H, Fe(IV), and 1O2 are the favored oxidants for As(III), while ROS, 3O2, and Fe(III) possess the capability to convert As(IV) to As(V). The major mechanism of As(III) oxidation in the presence of pyrite without light irritation primarily involves three elementary reactions: (1) center dot OH facilitating As(III) conversion to As(IV), (2) 3O2 oxidizing As(IV) to As(V) and center dot O2H, and (3) As(V) and center dot OH generating in center dot O2H reacting with As(III). As(IV) emerges as a critical intermediate capable of initiating chain reactions in arsenic oxidation. This study provides atomic -scale insight into the As(III) oxidation in pyrite suspension, which is important for understanding arsenic behavior in analogous oxidation systems.