Interaction between green rust and tribromophenol under anoxic, oxic and anoxic-to-oxic conditions: Adsorption, desorption and oxidative degradation

As a reductive Fe(II)-bearing mineral, green rust (GR) is able to reduce halogenated compounds in anoxic subsurface environments. The redox condition of subsurface environment often changes from anoxic to oxic due to natural and anthropogenic disturbances, but the interaction of GR with halogenated compounds in oxic, and anoxic-to-oxic transition conditions has not been studied. This study reveals that GR can sequester TBP for a short time (4 to 10 h) under anoxic conditions. Later, GR undergoes structural transformation to ferrihydrite and magnetite with the desorption of TBP. GR-derived iron (hydr)oxides can generate 33.8 μM of •OH upon 50 h exposure to dioxygen, which leads to 67% of oxidative degradation of TBP. The anoxic-to-oxic transition during the TBP adsorption process initiates the TBP desorption immediately, and also results in the oxidative degradation of TBP via the production of •OH. The oxygenation of GR immediately forms magnetite which activate dioxygen to produce •OH. Also, the GR-derived magnetite acts as a Fe(II) source, and free Fe(II) in solution and Fe(II) adsorbed on magnetite surface both contribute to dioxygen activation. This work provides vital evidence on the role of GR in the fate and transformation of TBP in redox alternating subsurface environments.